Juggle levels on rifles

CBA Member

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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CBA Member

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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Standard Member

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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CBA Member

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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CBA Member

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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CBA President

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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CBA Member

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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CBA Member

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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CBA Member

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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CBA Member

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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CBA Member

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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CBA Regional Director

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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CBA Member

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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CBA Regional Director

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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Juggle levels on rifles

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