SHOT ELEVATION AND MV

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  • Last Post 20 February 2019
joeb33050 posted this 18 February 2019

Do changes in MV change shot elevation, over a set of shot with the same load?

I loaded 50 223 ctgs with 7.0 Titegroup and Hornady 68 gr hpbtm shot them at 50 different locations, measured MV and elevation, normalized the elevation numbers and graphed the results.

 

 

Changes in MV change elevation about .010"/fps or about 1"/100 fps, but MV and changes in elevation are not strongly correlated.

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x101airborne posted this 18 February 2019

That is interesting.

In your experiments did you find accuracy stayed the same for the given load, just the distance from point of aim shifted a bit?

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RicinYakima posted this 18 February 2019

Even at those light loads, barrel harmonics are a factor. Overlapping sine and cosine waves are not my strong suit, but good math guys could give you some insight.

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joeb33050 posted this 18 February 2019

That is interesting.

In your experiments did you find accuracy stayed the same for the given load, just the distance from point of aim shifted a bit?

No groups, 50 shots, each at a different aiming point.

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joeb33050 posted this 18 February 2019

Even at those light loads, barrel harmonics are a factor. Overlapping sine and cosine waves are not my strong suit, but good math guys could give you some insight.

I've never understood the barrel harmonics (or harmonica) story. I think that the barrel harmonics guys are talking about barrel vibrations, and the RF guys seem to tune barrels-maybe. Any time I attacked a math explanation, it fell apart. Maybe barrel vibrations belong in the dumpster with cryogenic, hdpe/ldpe/sorta dpe wads; moly coating, and  orienting.

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John Carlson posted this 19 February 2019

I once had a 22-250 with which increasing velocity resulted in a lower POI.  I figured it had to do with recoil mechanics.  As the bullet starts to move the barrel both recoils back and rotates up according to how far the barrel is above the stock.  I figured maybe the faster bullets were exiting the muzzle before it had time to rise as far as with slower bullets.  But then there's the question of why none of my other rifles do that.  Time to go cast some more bullets, out in the shop, next to my fridge...................

John Carlson. CBA Director of Military Competition.

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Ken Campbell Iowa posted this 19 February 2019

oh wow, i just had a thought that this test needs to sample the bullet position at 2? distances ... to cancel out the effect of the muzzle pointing in different directions/angles at different shots ...  

i demand that faster bullets drop less !! ...  i am confused by real-life results ...depressed

ken

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Larry Gibson posted this 19 February 2019

Fifty  different 1 shot "groups"........

How did you determine if that "1 shot" was a high, low or in between shot in the actual cone of fire of that load?

LMG

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

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joeb33050 posted this 19 February 2019

Fifty  different 1 shot "groups"........

How did you determine if that "1 shot" was a high, low or in between shot in the actual cone of fire of that load?

LMG

Here's how I did it, without mentioning the "cone of fire".

Level a bought target with lines 1" apart on the 200 meter holder

Accentuate the center elevation line intersections every 2", for 10 intersections.

On another target, zero the scope/rifle.

Raise the scope elevation (Weaver T36) 16 clicks, ~4".

Aiming at the accentuated intersections, fire 10 shots l to r. (~4' high)

Lower the scope elevation 8 clicks, fire another 10 shots at the same aiming points. (~2" high)

Lower the scope elevation 8 clicks, fire another 10 shots at the same aiming points. ( centered elevation)

Lower the scope elevation 8 clicks, fire another 10 shots at the same aiming points.(2" low)

Lower the scope elevation 8 clicks, fire another 10 shots at the same aiming points. (4" low)

And record the MV for each shot.

Prepare a table of MVs, "TOP = !", numbered columns 1 to 5, 10 rows per column.

Measure the height of each shot above any convenient horizontal line.

Prepare a table of elevations like the table of MVs.

Find the average of each column of MVs.

Add negative and subtract positive column averages to each elevation, making a new table

I then added 2" to each elevation in the second table, making all elevations positive.

Now I made a list of MV and corresponding elevation, sorted and graphed

The EXCEL workbook is available on request.

The 200 METER range increased the click values)

 

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Larry Gibson posted this 19 February 2019

What is the fps ES for that load (50 shots) and what is the group size (cone of fire) when fired at one level?  Such will give us a "standard" for comparison.

Your graph shows both when fired at different levels but is there a difference between your test and a "standard" when fired at one elevation.  It has been known for some time that with a given zero at longer ranges (longer than 50 or 100 yards such as the 200m you used) with a given load the rounds having a higher velocity most often hit higher within the cone of fire. 

LMG

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

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joeb33050 posted this 19 February 2019

What is the fps ES for that load (50 shots)

100 fps

and what is the group size (cone of fire) when fired at one level?

Who knows?

  Such will give us a "standard" for comparison.

Comparison of what?

Your graph shows both

both what?

when fired at different levels but is there a difference between your test and a "standard" when fired at one elevation.

Show me the data!

 

It has been known for some time that with a given zero at longer ranges (longer than 50 or 100 yards such as the 200m you used) with a given load the rounds having a higher velocity most often hit higher within the cone of fire. 

What you want to do is read this sentence, over and over, until you begin to laugh. Faster bullets hit higher? Isn't that what my test data shows? 

LMG

I wonder if Ed likes your comments.

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Larry Gibson posted this 20 February 2019

It has been known for some time that with a given zero at longer ranges (longer than 50 or 100 yards such as the 200m you used) with a given load the rounds having a higher velocity most often hit higher within the cone of fire. 

What you want to do is read this sentence, over and over, until you begin to laugh. Faster bullets hit higher? Isn't that what my test data shows? 

My questions were just an attempt at further discussion and seek a bit of clarification of the interesting test you conducted, they were not criticism. 

"and what is the group size (cone of fire) when fired at one level?

Who knows?

  Such will give us a "standard" for comparison.

Comparison of what?"

A comparison of what your test reveled (your test results and your conclusion) compared to a similar result of what is normally done (the comparison group..."standard") would simply have given us a side by side comparison.

"Your graph shows both

both what?"

The ES and group size as asked in the previous sentence.  With your further explained details of how you conducted the test I see you actually, in a round about way, can measure both. Also based on that further explanation if you over lap the different aiming points to the same point you did, actually fire one 50 shot group. 

"when fired at different levels but is there a difference between your test and a "standard" when fired at one elevation.

Show me the data!"

That is a question joe. You apparently misconstrue what was stated.   It says "is there" which is a question.  It does not say "there is" which would be a statement alluding to other "data".  This is your test, the question was asking about other data you may have had. 

The premise of your test was; " Do changes in MV change shot elevation, over a set of shot with the same load?"

Yes, you certainly "proved" what was already known, and has been known for many years........in a very interesting manner.  Thanks for the information.

LMG

"I wonder if Ed likes your comments."

Sorry joe, but you've lost me on this one..........

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

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JeffinNZ posted this 20 February 2019

It took me a little bit to get my head around this one but I can be a tad slow on the uptake.

Joe, to me it looks like a representation of a 50 shot 3 inch group.

Cheers from New Zealand

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joeb33050 posted this 20 February 2019

It took me a little bit to get my head around this one but I can be a tad slow on the uptake.

Joe, to me it looks like a representation of a 50 shot 3 inch group.

WELL, THERE'S NO WINDAGE DATA, so it's not about a group.

I have/had a strong opinion that moving the gun from bull to bull on a, for example, 10 bull target, causes the point of impact to change. This would introduce error in the above test results. To experiment, this morning I shot 2 10 bull targets, 5 shots per bull, Ruger Charger, Kidd barrel and trigger, CCI SV, Weaver T36, 50 yards.

First target 5 at 1 bull, 5 at next bull... Average .658"

Next target, 1 at each bull, then 1 at each bull... Average .673"

So, if there is such a POI change, it isn't a big one.

And, Friday I'll repeat the test at 100 yards with a rimfire gun. Then we can calculate the 50 shot group size. Thank God for Euclid. 

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