Juggle levels on rifles

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  • Last Post 26 March 2016
John Alexander posted this 21 March 2016

That is supposed to be bubble levels but I know see how to change it. Oh well.

 Little tiny levels have been used on target rifles, especially long range target rifles for a long time to avoid canting the rifle or maybe to allow canting it the same amount for each shot. They seem to make sense at least in theory for iron sighted rifles.  However, I have always wondered why they might be useful for scopes with a horizontal cross wire that lets you control can't very precisely by alining the cross wire with something horizontal in the field of the scope (top of targets. target frames etc.) which seem intuitive and natural and doesn't require that you divert your eye from the target.

Strangely, i have never heard it discussed why it makes sense to hang a level on the outside of a scope and I'm curious.  Thoughts anyone?

John

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Brodie posted this 21 March 2016

Looking at the prices Mid Way wants for them I have to wander which precious metal they are made from.

B.E.Brickey

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RicinYakima posted this 21 March 2016

When I first started shooting benchrest BR22, my mentor told me that “almost always” the concrete, iron, etc. used in make the berm/target holder was level. So that is what I have always used when setting up the front rest. The benches are not level, especially the wooden ones. And I thought that is why you had two screw legs on the front, to adjust for bad benches.

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onondaga posted this 21 March 2016

http://www.castbulletassoc.org/view_user.php?id=6375>John Alexander

"I have always wondered why they might be useful for scopes with a horizontal cross wire that lets you control can't very precisely by aligning the cross wire with something horizontal in the field of the scope (top of targets. target frames etc.) which seem intuitive and natural and doesn't require that you divert your eye from the target."

Intuition and nature are something irrelevant to level John. My range has so much optical delusion that I use a carpenters level to locate targets level on target stands at the range. Targets being level to the planet's gravity then makes scope level valid when the scope level is set to the square of the rifle.

There is no diversion of the eye from the target when both eyes are open to see a target and a scope mounted level to the side as the Vortex. Unfortunately, that is much worse to keep both eyes open for some people than is walking and chewing gum...they fall down in confusion chewing gum and walking. They get double vision at the bench. it is a trainable situation and some just won't make the effort to help themselves. They shoot worse in general instead.

It is amazing how off level things can look to the eye due to the surroundings and due to how crookedly a scope was mounted. These things are easily overcome with a bubble level that relates to the planet's gravity.

I set scopes so the horizontal wire is tangential to gravity and the level of the firearm. This looks very wrong to people that set up scopes to be comfortable to their hold. They rarely listen and think all my scopes are crooked. I say they are at fault and wrong centering on their comfort. Being comfortable has problems. They have more diagonal dispersion than I do.

There are also people that refuse to believe the correct way to measure between a shooting position and a target on a slope is the plumb up distance between the two points regardless of the slope angle. They miss stuff and I don't. A five foot shot at at squirrel 100 feet up doesn't compute to a mind like that. If a squirrel dropped a nut and it lands 5 feet from your boot, it is a 5 foot shot to the squirrel no matter how high he is. They really lose it when you tell them the opposite is true too. It is just physics and I have a bag of noses to prove it.

Gary

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joeb33050 posted this 22 March 2016

John Alexander wrote: That is supposed to be bubble levels but I know see how to change it. Oh well.

 Little tiny levels have been used on target rifles, especially long range target rifles for a long time to avoid canting the rifle or maybe to allow canting it the same amount for each shot. They seem to make sense at least in theory for iron sighted rifles.  However, I have always wondered why they might be useful for scopes with a horizontal cross wire that lets you control can't very precisely by alining the cross wire with something horizontal in the field of the scope (top of targets. target frames etc.) which seem intuitive and natural and doesn't require that you divert your eye from the target.

Strangely, i have never heard it discussed why it makes sense to hang a level on the outside of a scope and I'm curious.  Thoughts anyone?

JohnI have tested the ability of people to judge level without a reference, and found that they could judge level to a very small error. Crosshairs on a scope can be leveled amazingly accurately by eye, no reference. No level is needed.

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joeb33050 posted this 22 March 2016

John Alexander wrote: That is supposed to be bubble levels but I know see how to change it. Oh well.

 Little tiny levels have been used on target rifles, especially long range target rifles for a long time to avoid canting the rifle or maybe to allow canting it the same amount for each shot. They seem to make sense at least in theory for iron sighted rifles.  However, I have always wondered why they might be useful for scopes with a horizontal cross wire that lets you control can't very precisely by alining the cross wire with something horizontal in the field of the scope (top of targets. target frames etc.) which seem intuitive and natural and doesn't require that you divert your eye from the target.

Strangely, i have never heard it discussed why it makes sense to hang a level on the outside of a scope and I'm curious.  Thoughts anyone?

John CANT WE ESTIMATE LEVEL?               I made a rig to test people's ability to estimate level.  A 3 foot metal ruler, a screw/nut/washer, a big piece of cardboard and some figuring gave me a calibrated measuring apparatus. I set the rig up so that when the ruler touched the mark numbered 15, the ruler was level.  I asked people to tell me to move the ruler up and down until they thought it was level, and then wrote the reading down. With 45 measurements the average was 14.67 and the standard deviation was .387.  What this tells us is that people can estimate level pretty well. They were about 1/3 of a degree off on average (15-14.67), maybe because of the design of the test rig. The standard deviation was just under 4/10 of a degree, meaning that 68% of the time accuracy is +/- .4 degree, 95% of the time accuracy is +/- .8 degree, and 99% of the time accuracy is +/- 1.2 degrees.             My impression is that with a more precise and better designed apparatus, and with practice, the variation would be reduced-people are probably able to estimate level better than the results indicate.   Measuring cant I set up to measure cant using two rifles, a Maynard #16 1882 and a C. Sharps M1885,  with iron sights on both and a scope on the Sharps. A piece of plastic pipe, a nail, a bottle with a big envelope held on with a rubber band, a bench rest and some trig and we were off. It is setups like this that cause my wife to call one of the kids and talk a long time.       Maynard, 20 tests, looking at a blank piece of white paper Standard Deviation .73 degrees Max Left Deviation  .86 degrees Max Right Deviation 1.52 degrees   Sharps 1875, 21 tests, Iron sights, looking at gray sky Standard Deviation .41 degrees Max Left Deviation  .93 degrees Max Right Deviation .69 degrees   Sharps 1875, 20 tests, 30X STS, looking at gray sky Standard Deviation .30 degrees Max Left Deviation  .39 degrees Max Right Deviation .61 degrees   The human eyeball can repeat level pretty well. Most of the time to within +/- one degree. And a flat or straight surface at the front sight aids that repeatability.
CONCLUSIONS             Canting the rifle doesn't matter as long as you do it the same for every shot.             Most of the time most people can tell what's level and repeat holding the rifle level so that cant doesn't matter much in the overall error equation.             For bench shooters, anti-cant devices solve the problem(if there is one.)             Black Powder long range and silhouette shooters love their spirit level front sights and believe that they can eliminate cant and increase accuracy using these sights. God bless them.            

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John Alexander posted this 22 March 2016

Joe, I remembered that you had done those canting test but had forgotten just how well people can estimate level even without aligning their horizontal crosshair with the top of the target frame.  Aligning the crosshair would surely be even more precise and as you point out there is no reason to actually be LEVEL as long as any cant is the same from shot to shot.

No one with any respect for actual numbers could seriously argue that one degree is going to cause any problem.

John

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Mike H posted this 22 March 2016

So long as you stick to short ranges and hold the rifle well you should be ok,however at long ranges a 1degree cant moves a 308 cartridge about 5” of windage at 1,000 yards.It is very easy to exceed this error through the course of a shoot if the shooter isn't extremely carefull.

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joeb33050 posted this 22 March 2016

John Alexander wrote: Joe, I remembered that you had done those canting test but had forgotten just how well people can estimate level even without aligning their horizontal crosshair with the top of the target frame.  Aligning the crosshair would surely be even more precise and as you point out there is no reason to actually be LEVEL as long as any cant is the same from shot to shot.

No one with any respect for actual numbers could seriously argue that one degree is going to cause any problem.

JohnJohn; The thing that still impresses me is that on an analog = has hands wall clock, one minute is 6 degrees. joe b.

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John Alexander posted this 22 March 2016

Mike H wrote: So long as you stick to short ranges and hold the rifle well you should be ok,however at long ranges a 1degree cant moves a 308 cartridge about 5” of windage at 1,000 yards.It is very easy to exceed this error through the course of a shoot if the shooter isn't extremely carefull. Thanks for the correction.  Even though that may be, I know that when I was shooting 1,000 yard matches with iron sights, five inches, (.5 moa) plus or minus was the least of my worries. I can see that it would be a concern with 1,000 yard benchrest shooters but then the big flat stocks resting on flat rests probably take care of that concern.

I am very skeptical that a shooter can hold to plus or minus 1 degree by watching a quarter inch bubble between two quarter inch marks in a one inch long level with one eye while shooting. Has this been determined? I am very confident that almost anybody can align a crosshair with ten feet of target frame better then 1 degree. Somebody would have to build a contraption like Joe's to find out -- an interesting project for someone.

John

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45 2.1 posted this 22 March 2016

^^^^^^^^^^^ This is supposing that the crosshair or bubble is actually in line with the bore and the rifle is level. Many folks set up isn't.

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joeb33050 posted this 22 March 2016

45 2.1 wrote: ^^^^^^^^^^^ This is supposing that the crosshair or bubble is actually in line with the bore and the rifle is level. Many folks set up isn't.What does this mean?What is the “This” in “This is supposing..."?

There is no “level” for a rifle, no rifle is “level” because there is no datum plane. A bolt gun is essentially round when viewed from the end. We might agree that with a front sight on the rifle, that the line from bore center to front sight top is normal to = 180 degrees from the “level” plane, but that's merely a convention.

A bubble mounted on the gun is a reference, an agreed upon “level” line or plane.

A stud is level when a level placed on the stud reads level. A rifle has no such surface.

A rifle has no level line or plane, except as convention.

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joeb33050 posted this 22 March 2016

Mike H wrote: So long as you stick to short ranges and hold the rifle well you should be ok,however at long ranges a 1degree cant moves a 308 cartridge about 5” of windage at 1,000 yards.It is very easy to exceed this error through the course of a shoot if the shooter isn't extremely carefull. 8.3 CANT               Look at a clock. When the hand moves one minute, it has moved six degrees. Yes it has. A degree is a small bit of angle. Cant in a handgun is not considered a problem, so this is about rifles. Cant is the tilting or rotation of a rifle about its long axis. Canting the rifle differently from shot to shot varies the point of impact of the bullet on the target. Rotating the rifle to the right moves the impact point to the right and down; rotating the rifle to the left moves the impact point to the left and down.             Bob Fitzgerald is one of the better and more reliable offhand shooters in the Old Colony Sportsman's Association, and he holds the rifle at a substantial cant angle. Cant doesn't bother his shooting because he holds the rifle at the same angle for each shot.             The most important thing to know about cant is that if the rifle is positioned the same for each shot, then there is no change of the impact point of the bullet due to cant, from shot to shot.             More precisely, cant is the rotation of the rifle about the axis going through the sights and the center of the target. The shooter will keep the sights aligned with the center of the target, and canting will rotate the rifle about the line going through the sights and to the target. As the rifle is rotated the impact point of the bullet moves in a circle of radius = drop of the bullet and center at the zero cant impact point - drop.  Let's say that the drop is 6” over some range, and you have zeroed the rifle with no cant. Canting the rifle moves the bullet through a circle of 6” radius, and the center of the circle is 6” below the beginning, zero cant impact point.   Let R = radius and C = the cant angle in degrees, then horizontal deflection of the impact point = R Sin C and vertical deflection = -R-(R Cos C.)             The movement of the impact point is a function of the bullet drop and the angle of cant. For any cant angle up to 10 degrees or so, the amount of vertical shift is a small fraction of the horizontal shift, and can be ignored for most applications.             Drop is a function of muzzle velocity and the Ballistic Coefficient (BC) of the bullet, and is easily estimated on a personal computer using one of the ballistics programs that are readily available.             A plain base cast bullet has a typical BC of .4, and is fired at around 1400 feet per second (f/s.) That bullet will drop 9.5” in 100 yards and 1449” in 1000 yards. Canting the rifle to the right, for example, moves the impact point to the right and down thus:   Cant (degrees)              100 yd             100 yd             1000 yd        1000 yd                                               right”                down”              right”                down” 1                                    .166               .001                   25.3                   .221 2                                    .332               .006                   50.6                   .883 3                                    .497               .013                   75.8                 1.986 4                                    .663               .023                 101.1                 3.530   A typical .30 caliber jacketed bullet might have a BC of .5 and muzzle velocity of 2700 f/s. That bullet will drop 2.5” at 100 yards and 414 inches at 1000 yards.   Canting the rifle to the right, for example, moves the impact point to the right and down thus:   Cant (degrees)              100 yd             100 yd             1000 yd        1000 yd                                   right”                down”              right”                down” 1                                  .044                 .000                   7.2                   .063 2                                  .087                 .002                 14.5                   .252 3                                  .131                 .003                 21.7                   .568 4                                  .174                 .006                 28.9                 1.009               From the above it is clear that the downward or vertical shift in the impact point is a small fraction of the horizontal shift, and that the horizontal shift varies directly with the cant angle. See above, 1 degree gets .044”, 2 degrees gets .087” which is twice .044”(forgetting rounding errors,) and so on. The horizontal shift at 5 degrees is 5 times the 1 degree shift.             Then forgetting the relatively small vertical shift, the horizontal shift resulting from canting the rifle 1 degree is simply a function of the bullet drop, thus:   Drop”               1            2            4            8            16            32            64            128            256            512            1024    Hor Shift”            .017            .035            .070            .140            .279            .558            1.12            2.23            4.47            8.94            17.9       Estimating the horizontal shift for any cant angle and any drop is done by interpolating and multiplying. The horizontal shift caused by canting a rifle 3 degrees when the drop is 432 inches is estimated so:                         to interpolate: 4.47”+((432”/256”) X 4.47”) = 7.5” = 1 degree cant horizontal shift                         then multiply: 7.5” X 3 = 22.5” = 3 degree cant horizontal shift

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Scearcy posted this 22 March 2016

I am sorry Joe but I must respectfully disagree.  Math is a great tool if the base line assumptions are a perfect fit for the physical realities of the problem being addressed.  I am not sure how the 6” radius of error is calculated but I believe it to be wrong and here is why.  In the real world, the assumption that the line of sight is the radius around which everything rotates - and that all else is unchanged simply doesn't hold.  The front and rear bags are are the fixed points in our game.  While we strive to correct the sight picture as the cant of the rifle changes, it is not correcting for a simple rotation.  The lever arm from the bore to the front bag is smaller than the lever arm from the line of the bore to the rear bag.  At a minimum maintaining the sight picture as a rifle is rotated requires changes in the position of the stock on both the front and rear bags.  Mathematically this may not be a big deal but it also affects the “hold” on the rifle and the recoil characteristics during the follow through.  Are these effects large?  Likely not, but they are cumulative. While I have no way to prove it, I believe the 1/2 moa per degree estimate WHEN USING A HUNTER CLASS RIFLE.  The straight stock of a typical heavy rifle would reduce the effect even if the wide fore end allowed cant to occur.  The thing is we worry about wrinkled bullets, weighing bullets, frosted (or unfrosted) bullets, etc even though we can not prove the detrimental effect on accuracy.  If you cant a rifle, you are guaranteeing a change of impact.  Over the course of a 10 shot group, it is entirely possible than the rifle will be canted both to the left and the right.  1 degree each direction could introduce an “intentional error” of 1 inch if the 1/2 moa estimate is approximately correct.  In a well shot match, this is going to increase your group size by 50% to 100%.  I ask you why would you do this? Cost?  I wouldn't think so.  Any old rifle/scope combination is going to cost nearly $1,000 at todays prices.  An extra expenditure of $50 give or take to mitigate (not eliminate) any error due to canting your rifle seems to be a wise investment. I am not trying to be argumentative this morning, I am just saying why wouldn't you reduce this effect if you can? Jim

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joeb33050 posted this 22 March 2016

JHS wrote: I am sorry Joe but I must respectfully disagree.  Math is a great tool if the base line assumptions are a perfect fit for the physical realities of the problem being addressed.  I am not sure how the 6” radius of error is calculated but I believe it to be wrong and here is why.  In the real world, the assumption that the line of sight is the radius around which everything rotates - and that all else is unchanged simply doesn't hold.  The front and rear bags are are the fixed points in our game.  While we strive to correct the sight picture as the cant of the rifle changes, it is not correcting for a simple rotation.  The lever arm from the bore to the front bag is smaller than the lever arm from the line of the bore to the rear bag.  At a minimum maintaining the sight picture as a rifle is rotated requires changes in the position of the stock on both the front and rear bags.  Mathematically this may not be a big deal but it also affects the “hold” on the rifle and the recoil characteristics during the follow through.  Are these effects large?  Likely not, but they are cumulative.

I'm pretty sure that the arithmetic is correct. As for the rest of your arguments, I don't know. However, if, as my tests show, people can level the gun by eye pretty well/consistently; I'd suggest that the effect of your arguments is small. But; I don't know.

While I have no way to prove it, I believe the 1/2 moa per degree estimate WHEN USING A HUNTER CLASS RIFLE.  The straight stock of a typical heavy rifle would reduce the effect even if the wide fore end allowed cant to occur.  The thing is we worry about wrinkled bullets, weighing bullets, frosted (or unfrosted) bullets, etc even though we can not prove the detrimental effect on accuracy.  If you cant a rifle, you are guaranteeing a change of impact.  Over the course of a 10 shot group, it is entirely possible than the rifle will be canted both to the left and the right.  1 degree each direction could introduce an “intentional error” of 1 inch if the 1/2 moa estimate is approximately correct.  In a well shot match, this is going to increase your group size by 50% to 100%.  I ask you why would you do this? Cost?  I wouldn't think so.  Any old rifle/scope combination is going to cost nearly $1,000 at todays prices.  An extra expenditure of $50 give or take to mitigate (not eliminate) any error due to canting your rifle seems to be a wise investment. I am not trying to be argumentative this morning, I am just saying why wouldn't you reduce this effect if you can?

I don't disagree. I've had rifles with spirit level front sights, and could not hold, align sights, yank the trigger AND center the bubble. Some say they can. I think of the bubble level as akin to the auto tachometer, im,pressive but not used all that much.

JimThe Stanley replacement vial for ~$1.50 at the hardware store fits nicely on a weaver base, probably others. Glues on?

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45 2.1 posted this 22 March 2016

joeb33050 wrote: A rifle has no level line or plane, except as convention. Gunsmiths know otherwise....... They'll find one when they have to drill and tap for a scope. It makes one wonder how the  factories get those mounting screws on top of the action, now doesn't it.

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joeb33050 posted this 22 March 2016

45 2.1 wrote: joeb33050 wrote: A rifle has no level line or plane, except as convention. Gunsmiths know otherwise....... They'll find one when they have to drill and tap for a scope. It makes one wonder how the  factories get those mounting screws on top of the action, now doesn't it. It doesn't make me wonder. The action, think Savage/Remington etc that starts life as a piece of tube, has one of the beginning cutting operations define a datum. All from then on references this datum and/or others that originate here. The action goes in a fixture that references the datum, scope mount holes are drilled. It's easy. The operator is without knowledge of the datum or any fixture. Note that the datum is a convention, must be because of the geometry of the action, if made from tube. Springfield, 1917, Win 70 have flats at bottom of the action. IIRC. Flats make nice datum if it is/was a datum..

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Scearcy posted this 22 March 2016

I check mine just as I am starting the squeeze.  Not fool proof but makes me feel better. :)

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Tom Acheson posted this 22 March 2016

Does it make you wonder why a lot of the front sight assemblies for BPCR guns have a built-in level? These are for iron sights at 200, 300, 385 and 500-meters in the NRA steel silhouette game and the 1,000-yard BPTR game. They are there for a reason, right? I check mine before each shot. Funny how much you change the position of the gun without realizing it and just assume you are “holding” the same.....

Tom

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joeb33050 posted this 22 March 2016

I was a member of the Original Pennsylvania 1000 yard bench rest club for a few years, everyone/almost shot a scope, I don't remember a single level.

Do the 1000 yard Camp Perry guys use levels? Irons at 1000?

Maybe I'll go into the level business.

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Tom Acheson posted this 22 March 2016

There is a club 45-minutes north of here that shoot 1,000-yard matches, everyone using a scope.

BPTR=Black Powder Target Rifle. Take a trip to the NRA Whittington Center near Raton, NM this summer. Be there during the National Tournament...take a look around at the guns and the shooter “behavior". It is educational.

You'll not get rich selling those little levels.

Tom

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John Alexander posted this 22 March 2016 

      I am happy that my original question starting this thread has stirred up a lot of conversation. I have enjoyed the back and forth which has raised other interesting questions and even some subjects for additional experimentation.

  I conceded that there may be a role for spirit levels on iron sights for very long range in my first sentence.    However,  no one (but myself in post 10) has ventured an opinion or fact in response the to actual question I asked.   “     I just find it hard to believe that a tiny spirit level is as precise as using the crosshair and target frame. Are there any thoughts or evidence on this comparison of spirit level to crosshair?  The precision possible with a one inch long spirit level must be known.

John

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Brodie posted this 22 March 2016

John, Assuming that the top of the target frame --or whatever reference you use-- is level it is most likely more precise than a small spirit level that you may have to take your eye off the target or away from the scope to use.  Besides that I personally would feel silly messing with the level while shooting.  Because of not being able to shoot while watching the level f(unless you have trained yourself to shoot with both eyes open and the level is easily viewed by your off eye) I would say that lining the cross hair up with either a known vertical  or horizontal line is the better choice. Brodie \

B.E.Brickey

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Scearcy posted this 22 March 2016

Back in the day we used 1 inch spirit levels hung from a string line to level the forms for house and garage foundations.  Eventually the boss could afford a tripod mounted transit and stick to do the leveling.  Funny thing the tripod was leveled with a spirit bubble. This doesn't prove a thing other than my last name is not Kennedy or Dupont.  I am just saying don't sell a simple bubble level short.  I agree with you though John.  Some engineer must have the specs to quantify their accuracy. Jim 

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Scearcy posted this 22 March 2016

I am not sure this helps but it does address the potential of a spirit level. www.leveldevelopments.com/sensitivity-explained/

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Pentz posted this 23 March 2016

"level” will be constant if one assumes the scope rail to be level as a reference point. Then one levels the horizontal hair of the scope level with the rail. I have a line level attached even with the base of my staple gun, and level the target with it. Looking through the scope, level with the target base (or lines) set your scope to level with the scope hair. If the scope hair is not level with the target lines or base then your rifle ain't level. Works for me YMMV.

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Westhoff posted this 23 March 2016

Re JHS's comment about using a transit to level (and plumb) concrete foundation and wall forms: I spent a lot of years running survey crews both on building/bridge etc construction and high rise structures. When you level a transit - or a tripod mounted level - first you level the instrument facing 90 deg. away from your target. Then you level the instrument facing your target, then you level it facing 180 deg. away from the target. If there is a disparity you keep adjusting the leveling screws until the bubble is off the same amount either way.

This method (and enough practice) can assure you of being pretty much within 0.01 inch from any one setup.

Honest!

Wes P.S.  Obviously, this is NOT a procedure anyone is going to use from a shooting bench- at least not more than once!

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John Alexander posted this 23 March 2016

Jim's reference and Wes's experience as a surveyor are right on.  I also was a surveyor in another life and the “Two Peg Test” that Wes describes can be used to adjust the level on a transit or better yet an engineer's level to do very precise work -- no question about it.  The question isn't can a spirit level be made that will do very precise work like the very expensive ones on an engineer's level.  The the question is are the ones sold to us shooters precise enough to be able to determine level well enough -- or as good as just using the crosshair in the scope.  I guess I will have to buy one of the darned things and test it to find out.

As Joe pointed out there is absolutely no need to have the target frame used for alignment to actually be level.  All is needed is to have the cant of the rifle be the same for each shot.

John

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Pentz posted this 23 March 2016

All is needed is to have the cant of the rifle be the same for each shot. Exacterly....;)

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45 2.1 posted this 23 March 2016

John Alexander wrote:  The question isn't can a spirit level be made that will do very precise work like the very expensive ones on an engineer's level. 

  All is needed is to have the cant of the rifle be the same for each shot.

John

I am an engineer who has surveyed items for the last 50 years with civil war era transits to the latest stuff. Most of the old transits had better level bubbles than what is on the new electronic stuff. I would trust both implicitly though once checked to be correct. The best thing to do is check anything new against a proven level or circuit, just to be sure as most bubble/string levels not attached to an instrument aren't quite there.

The same cant works fine until you go to longer ranges, then if it wasn't plum you have to start adjusting windage.

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RicinYakima posted this 23 March 2016

No one seems to have mentioned that bubble levels are made with different degrees of angularity .

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John Alexander posted this 23 March 2016

RicinYakima wrote: No one seems to have mentioned that bubble levels are made with different degrees of angularity . That was in Jim's link.  I should have mentioned it directly.  i doubt if the tube in my $10  torpedo level is the same quality as in an engineer's level

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gpidaho posted this 23 March 2016

I worked construction for 45yrs. and can say that spirit levels in general are a sort of “close enough” kind of tool. We NEVER trusted one, even a six foot long one with ANYTHING important. Drop a Plumb Bob and measure a six-eight- ten right triangle off that or use a site level (transit) Spirit levels are best used as a lever to roll logs. JMHO Gp

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Larry Gibson posted this 23 March 2016

Spirit levels on rifles are one of the beneficial tools a long ranges shooter can use to ensure accuracy, especially 1 shot accuracy on small targets.

I do agree that on sterile ranges with level or reasonably level firing lines, benches and targets (especially those on square frames) it is not to difficult for a practiced shooter to level a rifle w/o a sprit level, especially if it has a correctly mounted scope that has the vertical cross hair inline with the bore.  It is even easy enough for a practiced  high power shooter to not need a sprit level at long range (1000 yds for example) because the shooter is maintaining a consistent position and has sighter shots to initially adjust/compensate for any discrepancy from canting the rifle. Spirit levels on long range BPC rifles have been in use for a 130+ years.  I have been on many HP ranges and have seen a lot of spirit levels on rifles, especially long range rifles used for 600 - 1000 yard competitions and on larger caliber rifles used for 1000+ shooting.  Probably a reason for that.    Because something is not used or we have not seen it used does not mean it is not useful.   I use a spirit level on my long range BPC rifle, my M70 .308W target rifle and my long range rifles.  On my target rifles with match iron sights I quickly found I was needing much less elev/windage changes after the 2 sighter shots to be in the 10 and X ring.  I see a lot of spirit levels on not only long range match rifles but on rifles used for long range target interdiction (2 and 4 legged targets) where to importance of a 1st round hit is imperative as there are usually not any sighter shots,  especially when shots go both ways.   I use spirit levels on some rifles when there is a potential benefit.  The usefulness of such use is well proven, at least to me.   LMG

Concealment is not cover.........

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RicinYakima posted this 23 March 2016

Gp, I was thinking more about my 8 inch machinist level on a granite plate.

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gpidaho posted this 24 March 2016

Ric: Agreed, I was speaking in reference to leveling backboards and shooting benches. Gp

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John Alexander posted this 24 March 2016

I just removed some posts that I judged had turned unnecessarily snarky and were talking past each other. When we disagree let's try to explain our point as clearly as possible and keep it polite while doing it. John

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gpidaho posted this 24 March 2016

In reference to the deleted posts: Well, once again revealing my lack of understanding and ignoring my own motto, I have to ask. When one is dealing with a tube (rifle barrel) that is threaded on one end for mounting in the receiver and adjusting headspace and possibly on the other for a brake or other device. This tube having rifling cut helically in it, some of even number some of odd. All this in a given length that may be shortened by crowning or just to make said barrel handier. How does one determine what is thought to be plumb before installing a front sight or drilling and tapping for scope base. A link or reference would be good, it may take more “Splainin” than handy on the forum. Thanks Gp

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Larry Gibson posted this 24 March 2016

gpidaho   The best way to drill and tap an action or the barrel for sights (scope bases, front or rear irons or aperture sights is with an appropriate jig.  I have use the Forster jig on a mill table mounted on a floor model drill press since 1970.  I have drilled and tapped many different kinds of receivers and barrels.  The flat bottom receivers are aligned via V ways with the holes drilled plumb to the flat bottom. With round bottom receivers a small lock bar aligns the bolt race ways to be plumb with the drilled holes.  The are also barrel V ways that keep the drilled holes in in the barrel in alignment with the barrel/action assembly.    Unless one is a very good machinist with a proper mill or drill press who understands how the sight(s) or bases must properly align with the action/barrel assembly it is best to have someone who is competent and has an appropriate jig for the intended purpose.  I have seen buggered jobs by individuals who attempted to use one of the simpler jigs available to D&T for a sight it was not intended for.  Many criticize good gunsmiths for what they charge to D&T.  They obviously don't realize the investment in equipment the gunsmith has and his knowledge to do the job correctly.  You can not “undrill” a hole that is in the wrong place on an action or barrel.      LMG

Concealment is not cover.........

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gpidaho posted this 24 March 2016

Thanks for the reply Larry. Rest assured if it's D&T required on one of my rifles it's going to a smith. The V ways explain a lot. Just still trying to get my head around how when the barrel length is changed and rifling changing it's position in relation to the end of the barrel(say 1 o'clock instead of noon) doesn't change what was originally plumb. Well, just thinking too much again, doesn't matter that I understand as I would let out the job of D&T anyway. Thanks Gp

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Ken Campbell Iowa posted this 24 March 2016

hi gp: your instincts are exactly right ... once a workpiece leaves the original jigging it was made in ... it creates problems in further machining .

one familiar example is ” blue-printing ” a factory action ... OMG! ... where do we start ?? ( usually we say the bolt raceway is good ... then we re-manufacture the action around that reference ... a bit scary, right ? )

and yep, barrels might not shoot straight .... that is why god made adjustable sights ... heh ...

ken

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Larry Gibson posted this 24 March 2016

Ken is correct, if there is any measurable change in poi from a change of the position of the rifling at the muzzle it is well within the adjustment range of the sights if they are installed correctly to begin with. That is referring to iron sights.

With reference to alignment of scope reticles there are numerous references to doing that correctly.

If the reticle is correctly aligned with the bore and the horizontal crosshair level then the trajectory of the bullet will be correct to the sight even if leveling the horizontal crosshair results in canting the rifle. This is because even with the rifle canted the bore and crosshairs are vertically aligned.  This situation occurs when an action is D&T'd slightly off to one side of the actions vertical centerline.

Conversely if the vertical crosshair is not aligned (plumb) with the center of the bore and we just level the crosshair the rifle's bullet trajectory will be canted. That's okay if we are just shooting at 1 range and are zeroed for that range and also if shooting closer. Shooting at any other range, particularly at longer ranges, will produce and error of inaccuracy left or right proportional to the distance from the zero range.

LMG

Concealment is not cover.........

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gpidaho posted this 24 March 2016

After a couple hours more thinking to much the dim bulb came on. I can now understand that the relation of the D&T only has to correspond to the given. That being the V and thanks for your thoughts and patience. I'll move on to obsessing over something else now! lol Gp

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Brodie posted this 24 March 2016

gpidaho, Your mind just isn't screwed up enough to make sense of the concept. Brodie:wavw2:javascript:emoticon(':wavw2:',%20'images/emoticons/party0018.gif')

B.E.Brickey

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gpidaho posted this 25 March 2016

Oh Brodie,if you only knew! The voices in my head have more fun in there than I have out here! Gp

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billwnr posted this 25 March 2016

When I shot NM Highpower my front sight had a level on the back of it. Prevented “off shots” from canting the rifle.

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John Alexander posted this 25 March 2016 

             This discussion has gotten a lot more interesting than I expected.  When it went from “is a spirit level better for controlling cant than the horizontal crosshair” to the the question of how important, or not, a few degrees of cant is and is that importance, or lack of importance, only at long range.  I will admit that my head was spinning at times until I thought -- wait this is a geometry problem and I had that as a sophomore in high school.  This isn't like trying to figure out what really happens to a cast bullet in the throat when the gun goes off.  We don't have to rely on guesses, opinions, what is written somewhere by an authority (who may be wrong) or “what everybody is doing.” I think I finally have the geometry problem straightened out in my head and you can explain to me why not if I am wrong.

  Assume we have a long range rifle with the long axis of the scope 2 inches above the axis of the bore and the axis of the scope (sight line) and the axis of the bore converging at 200 yards. (for what distance that convergence would zero the rifle would depend on velocity and BC of the bullet but is irrelevant for now ”€œ forget what the bullet is doing until later.)   Now assume that the rifle is canted 2 degrees from where it was uncanted the shot before.  Joe's experiments showed that shooters are amazingly good at eliminating cant, so 2 degrees is a lot.  By geometry (2” x sin 2 degrees) this puts axis of the bore 0.07” horizontally from where it was for the last shot in relation to the scope axis. The vertical deflection (2 ”€œ 2 x cos 2 degrees) = 0.001” so we can ignore the vertical change.  Both of these deflections are at the rifle and bench.   This will mean that although the sight line and axis of the bore will still converge at 200 yards, at 400 yards the bore axis will be located .07” to the opposite side that it was deflected towards back at the rifle.  At 1,000 yards the axis of the bore will be 0.28 inches from where it was for the uncanted shot before.   Where is the bullet? In some previously posts it was mentioned, or assumed, that the “trajectory was canted” when the rifle was canted.  This can't be.  Except for minor influences (latitude, twist, and direction rifle was pointed) and the usual major influence of wind, the trajectory will go relentlessly toward the center of mass of the earth (gravity) no matter how you cant the rifle.   If the analysis above is right then the error caused by inconsistent cant is equally important at all ranges ”€œ not much at all at. For instance  the error at 1,000 yards caused by a 2 degree change in cant is about a quarter of an inch (0.7” for a yough 5 degree cant).  Needless to say at a distance where the wind deflection may be varying in feet from one shot to the next this isn't the shooters biggest problem.  If there are errors in my thinking or calculations please let me know.   John    

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joeb33050 posted this 25 March 2016

John Alexander wrote: This discussion has gotten a lot more interesting than I expected.  When it went from “is a spirit level better for controlling cant than the horizontal crosshair” to the the question of how important, or not, a few degrees of cant is and is that importance, or lack of importance, only at long range.  I will admit that my head was spinning at times until I thought -- wait this is a geometry problem and I had that as a sophomore in high school.  This isn't like trying to figure out what really happens to a cast bullet in the throat when the gun goes off.  We don't have to rely on guesses, opinions, what is written somewhere by an authority (who may be wrong) or “what everybody is doing.” I think I finally have the geometry problem straightened out in my head and you can explain to me why not if I am wrong.   Assume we have a long range rifle with the long axis of the scope 2 inches above the axis of the bore and the axis of the scope (sight line) and the axis of the bore converging at 200 yards. (for what distance that convergence would zero the rifle would depend on velocity and BC of the bullet but is irrelevant for now ”€œ forget what the bullet is doing until later.)   Now assume that the rifle is canted 2 degrees from where it was uncanted the shot before.  Joe's experiments showed that shooters are amazingly good at eliminating cant, so 2 degrees is a lot.  By geometry (2” x sin 2 degrees) this puts axis of the bore 0.07” horizontally from where it was for the last shot in relation to the scope axis (no matter the center of rotation.) The vertical deflection (2 ”€œ 2 x cos 2 degrees) = 0.001” so we can ignore the vertical change.  Both of these deflections are at the rifle and bench.

I GET THE SAME NUMBERS, .0698 AND .00122.   This will mean that although the sight line and axis of the bore will still converge at 200 yards, at 400 yards the bore axis will be located .07” to the opposite side that it was deflected towards back at the rifle.  At 1,000 yards the axis of the bore will be 0.28 inches from where it was for the uncanted shot before.   YES, BECAUSE THE X HAIR CENTER IS ROTATING ABOUT THE ORIGINAL CENTER OF ROTATION, THE CENTER 2” FROM THE X HAIRS.

Where is the bullet? In some previously posts it was mentioned, or assumed, that the “trajectory was canted” when the rifle was canted.  This can't be.

AGREE

  Except for minor influences (latitude, twist, and direction rifle was pointed) and the usual major influence of wind, the trajectory will go relentlessly toward the center of mass of the earth (gravity) no matter how you cant the rifle.   If the analysis above is right then the error caused by inconsistent cant is equally important at all ranges ”€œ not much at all at any.

For instance  the error at 1,000 yards caused by a 2 degree change in cant is about a quarter of an inch (0.7” for a yough 5 degree cant).  Needless to say at a distance where the wind deflection may be varying in feet from one shot to the next this isn't the shooters biggest problem.  If there are errors in my thinking or calculations please let me know.   ONE OF US IS WRONG HERE. I WROTE:             More precisely, cant is the rotation of the rifle about the axis going through the sights and the center of the target. The shooter will keep the sights aligned with the center of the target, and canting will rotate the rifle about the line going through the sights and to the target. As the rifle is rotated the impact point of the bullet moves in a circle of radius = drop of the bullet and center at the zero cant impact point - drop.  Let's say that the drop is 6” over some range, and you have zeroed the rifle with no cant. Canting the rifle moves the bullet through a circle of 6” radius, and the center of the circle is 6” below the beginning, zero cant impact point.   Let R = radius and C = the cant angle in degrees, then horizontal deflection of the impact point = R Sin C and vertical deflection = -R-(R Cos C.)             The movement of the impact point is a function of the bullet drop and the angle of cant. For any cant angle up to 10 degrees or so, the amount of vertical shift is a small fraction of the horizontal shift, and can be ignored for most applications.             Drop is a function of muzzle velocity and the Ballistic Coefficient (BC) of the bullet, and is easily estimated on a personal computer using one of the ballistics programs that are readily available.             A plain base cast bullet has a typical BC of .4, and is fired at around 1400 feet per second (f/s.) That bullet will drop 9.5” in 100 yards and 1449” in 1000 yards. Canting the rifle to the right, for example, moves the impact point to the right and down thus:   Cant (degrees)              100 yd             100 yd             1000 yd        1000 yd                                               right”                down”              right”                down” 1                                    .166               .001                   25.3                   .221 2                                    .332               .006                   50.6                   .883 3                                    .497               .013                   75.8                 1.986 4                                    .663               .023                 101.1                 3.530 IS IT ME? John    

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John Alexander posted this 25 March 2016

Joe,

I think it is but I have been wrong once or twice before.  My reason is in this assumption which I believe is wrong:

"As the rifle is rotated the impact point of the bullet moves in a circle of radius = drop of the bullet and center at the zero cant impact point - drop.  Let's say that the drop is 6” over some range, and you have zeroed the rifle with no cant. Canting the rifle moves the bullet through a circle of 6” radius, and the center of the circle is 6” below the beginning, zero cant impact point."    The radius involved when the rifle is canted does not include the drop of the bullet.  If it did canting the rifle would swing the trajectory away from straight down (gravity). Canting the rifle can't affect trajectory except by where the muzzle is and what direction it is pointing then the bullet emerges. In a canted rifle the muzzle isn't directly under the scope axis (0.07” in the example). The direction is a bit different because the convergence angle between sight line and bore has rotated a bit from vertical.

We could argue a bit about the radius.  If you assume the rotation is about either the line of sight (keeping your eye on the target shooting in prone) or about the bore, the radius is 2” inches in my example.  If you assume that the center of rotation is where the stock rests on the bags then the radius would be the distance from the bags to the bore line -- maybe still near 2” or maybe a bit more depending on the shape of the stock.

John

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Scearcy posted this 25 March 2016

Joe and John Help me out here.  In Joe's example the bullet drops 9.5 inches in 100 yards.  Hence our scope is adjusted to offset that drop in order to place the point of impact on the point of aim.  While it would never happen, I think it is useful to consider what would happen if the rifle were canted 90 degrees.  If we ignore the effect of gravity, the bullet will strike 9.5 inches to the right of the point of aim.  That is how the rifle was adjusted when it was oriented vertically.  Gravity will only serve to drop the bullet 9.5 inches down as it always will - regardless of cant, in this example.  Now for a very small cant, the vast majority of the effect of gravity is offset by the initial scope setting as it always is.  I agree that lets ignore this for simplicity.  The question is, what is the horizontal deflection.  Assuming your formulae are correct, my disagreement is with the radius to which you are applying your geometry.  It seems to me the radius is 9.5 inches rather than 6 inches or 2 inches.  This would make Joe's deflection numbers even larger. The real deflection with which we are concerned here is the axis of the bore.  When the shooter reorients the point of aim back to the bull without correcting the cant, the axis of the bore remains on an arc of 9.5 inches but oriented 1 degree clockwise from vertical.  What am I missing?

Jim

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Larry Gibson posted this 25 March 2016

What also needs to be considered is that bullets do not travel in straight lines. Given a match .308W load at 2650 - 2700 fps it requires 35 +/- moa to go from a 200 yard zero to a 1000 yard zero. That changes the mid range from +1 3/4 - 2” to 12' +/-. A 1 degree cant moves the impact 5” at 1000 yards . The 2 degree cant in John's calculation would actually put the bullet 11+” to the side and low.

Given the amount of sight adjustment (elevation) needed on a BPCR to go from 200 to 1000 yards and the height of the midrange it's no wonder a spirit level is necessary for accurate shooting.

LMG

Concealment is not cover.........

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R. Dupraz posted this 25 March 2016

''Given the amount of sight adjustment (elevation) needed on a BPCR to go from 200 to 1000 yards and the height of the midrange it's no wonder a spirit level is necessary for accurate shooting"     Been there.

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joeb33050 posted this 25 March 2016

Let's see if this is correct. (I'm using up a lot of paper drawing.) Telescopic sights, John's example, 2” and 2 degrees The rifle is sighted in at a certain range. The rifle is canted-to the right. The cross hairs move right .07” and down .001". Now, the shooter who cants the rifle doesn't shoot with the scope aimed off, he moves the rifle/scope.

The shooter moves the butt of the rifle/scope to the right, moves the rifle/scope counter-clockwise viewed from the top, aligning the cross hairs and target once again.

The shooter also moves the butt of the rifle/scope up to center the cross hairs.

The canted rifle/scope now has the scope aligned with the target.

The displacement of the perfect bullets/perfect gun is now:

(Actual Range/Sight In Range) X Cant movement, W and E

So if the right movement is .07", and the sight in range is 200 yards, at 400 yards the displacement is (400/200) X .07” = .14", and at 100 yards is (100/200) X .-7” = .035".

At the sight in range there is NO displacement.

Note that it does NOT matter where the scope is located with respect to the rifle. The scope can be hooked to an apparatus and be three feet left and two feet high of the bore center, and with two targets placed properly, shot accurately. Aim at one, hit another. My 223...

Note that having the scope horizontal hair LEVEL when the rifle is held as the shooter wants, insures ONLY that W and E changes operate only on W and E. Think about a scope mounted so cross hairs form an X.

If the rifle is sighted in at the range the shooter wants to shoot at; and If the shooter moves the sight alignment to compensate for any cant-scope-movement; then cant means no displacement.

Then why the levels?

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Scearcy posted this 25 March 2016

Here is the scenario as it would play out for me. I fire my first of five shots for a group.  I am shooting in a match.  I push my rifle forward into battery again.  The cross hairs are 1/2” right of the dot.  Everything feels right but obviously something moved a little.  Do I: Move the rear bag slightly? Turn the windage screw on my front rest? Check the level on the scope before either of the above? Fire a sighter (different bull) and then repeat the above? I will check the bubble in the level.  The majority of the time, the cross hairs will come right back into alignment. If you touch the front screw and your rifle is canted slightly you will have unconsciously moved your point of aim.   If you always roll your rifle to get the crosshairs in place, a change in shoulder pressure may have moved your rear bag a few thousands of an inch and you will miss it, fire shot number 2 and then repeat the above. If you raise your rifle to the edge of the target to regain level, you have potentially moved both rests and the rifle.  See the paragraph above.

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Ken Campbell Iowa posted this 25 March 2016

hi guys ... please don't grab your 22 squirrel rifle and run out in your back yard and shoot 2 of 3 shot groups ....one scope straight up, one rifle rotated 90 degrees on the bench . show us the target .

please don't do this .. it would break the mood ...

heh

ken

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joeb33050 posted this 25 March 2016

JHS wrote: Here is the scenario as it would play out for me. I fire my first of five shots for a group.  I am shooting in a match.  I push my rifle forward into battery again.  The cross hairs are 1/2” right of the dot.  Everything feels right but obviously something moved a little.  Do I: Move the rear bag slightly? Turn the windage screw on my front rest? Check the level on the scope before either of the above? Fire a sighter (different bull) and then repeat the above? I will check the bubble in the level.  The majority of the time, the cross hairs will come right back into alignment. If you touch the front screw and your rifle is canted slightly you will have unconsciously moved your point of aim.   If you always roll your rifle to get the crosshairs in place, a change in shoulder pressure may have moved your rear bag a few thousands of an inch and you will miss it, fire shot number 2 and then repeat the above. If you raise your rifle to the edge of the target to regain level, you have potentially moved both rests and the rifle.  See the paragraph above.Agree. However, some are talking about LR rifle, which, as you know, ain't about what you're talking about. However, watching the level and removing cant works too, as you said. What doesn't work and doesn't happen, is canting the rifle, seeing the cross hairs off the center, and shooting anyhow. Nyet?

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Mike H posted this 25 March 2016

Speaking about long range hand held rifles.1,000 yard range,nominal 30minutes of elevation from zero30 minutes @ 1,000 yards = 300"Radius of 300” gives a diameter of 600” or 50 feetCircumference becomes 1,884"360 degrees in a circle,1884” divided by 360 = 5.2" If you look at a clock face,a minute doesn't look to be very far,divide that by 6 to get one degree,a lot less,now take stress,fatigue and all the concentration used to fire a shot,it is not hard to get some cant.I will keep using my level.Mike.

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Scearcy posted this 25 March 2016

Ken YOU ARE CORRECT SIR!  When I get home from my current winter break in Joe's fine state, I'll give it a try.  Hopefully someone will beat me too it. Jim

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John Alexander posted this 26 March 2016

The fatal flaw in my example in post #49 is that my assumption that the sight line and bore line converge at 200 yards.  I just pulled that out of the air arbitrarily.  Unfortunately that is totally unrealistic for real rifles especially cast bullet rifles. For instance in Joe's load which drops 9.5 inches in 100 yards the sight and bore line would have to cross at 21 yards for a 100 yard zero making all my computed deflections much much bigger.  For zeros for longer ranges the point where the sight line and bore line cross would be even closer to the muzzle making the deflections bigger and more important yet.

As usual, it it those darned assumptions that screw up all the nice logic or math that follows. 

John

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joeb33050 posted this 26 March 2016

JHS wrote: Here is the scenario as it would play out for me. I fire my first of five shots for a group.  I am shooting in a match.  I push my rifle forward into battery again.  The cross hairs are 1/2” right of the dot.  Everything feels right but obviously something moved a little.  Do I: Move the rear bag slightly? Turn the windage screw on my front rest? Check the level on the scope before either of the above? Fire a sighter (different bull) and then repeat the above? I will check the bubble in the level.  The majority of the time, the cross hairs will come right back into alignment. If you touch the front screw and your rifle is canted slightly you will have unconsciously moved your point of aim.

I don't think so. If you move your gun to align the sights, it's at the same point of aim. Your sentence below is correct.   If you always roll your rifle to get the crosshairs in place, a change in shoulder pressure may have moved your rear bag a few thousands of an inch and you will miss it, fire shot number 2 and then repeat the above.

We don't need a reference like the top of the target to level the rifle. I've shown this with test results that can be easily duplicated.

If you raise your rifle to the edge of the target to regain level, you have potentially moved both rests and the rifle.  See the paragraph above.

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joeb33050 posted this 26 March 2016

John Alexander wrote: The fatal flaw in my example in post #49 is that my assumption that the sight line and bore line converge at 200 yards.

I don't think so. The fatal flaw in all the discussions about cant is the failure to recognize that when the sights misalign because of cant, or anything else, that the shooter will re-align the sights. I got hung up on the arithmetic, describing a situation that will not exist. The shooter will align the sights, cant or not, and the bullet will hit center. Canted or level, with the sights aligned, the bullet hits center.

The arithmetic describes a situation where the rifle is canted, the sights are misaligned, and the shooter shoots anyhow.

The arithmetic goes on to talk about canted rifle, misaligned sights and shooting at other than the zeroed range.

If a rifle is canted, and if the sights are aligned, and if the range shot at = the sight-in range; then the bullet will strike center. (Or as close as it does with a level rifle.)

Scope and irons, same story. Ten minutes with pencil and paper convinces anyone.

This is a wheels-on-luggage moment.

 I just pulled that out of the air arbitrarily.  Unfortunately that is totally unrealistic for real rifles especially cast bullet rifles. For instance in Joe's load which drops 9.5 inches in 100 yards the sight and bore line would have to cross at 21 yards for a 100 yard zero making all my computed deflections much much bigger.  For zeros for longer ranges the point where the sight line and bore line cross would be even closer to the muzzle making the deflections bigger and more important yet.

As usual, it it those darned assumptions that screw up all the nice logic or math that follows. 

John

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John Alexander posted this 26 March 2016

Eating humble pie isn't so bad when you get used to it.  If I use a sight adjustment to elevate the muzzles that it actually takes to get zero at 1,000 which might be 30 moa or approximately 300 inches instead of the stupid 1 degree used in my example (convergence at 200 yd) my equation (300 inches x sin 1 degree) produces 5.2 inches of deflection similar to LMG's and Mike H's numbers. This is approximately .5 moa.

30 moa would be about the right sight elevation for a 311299 bullet with a MV of 1,800 fps at only  600 yards and much more at 1,000 yards so the deflection for such a cast bullet at a 1,000 yards would be quite a bit more.   Note that the midrange height of the bullet doesn't enter the calculation and doesn't need to be known -- just the sight adjustment needed.   For folks interested in deflections due to changes in cant in a CBA 100/200 yard match using the 299 bullet at 1,800 fps with the scope 2” above the bore, and the method above one degree cant would deflect the bullet 0.06” at 100 yards and 0.4” at 200 yards

John

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