Applied Ballistics 'Shoot Thru Target' Challenge

[bruce_ventura]

Bryan is not interested in the normal coning motion that all bullets experience when exiting the muzzle or encountering a crosswind in flight. This a precessional yaw motion somewhat like a spinning top that wobbles. When people usually talk about bullets "going to sleep" or seeing elliptical holes in target paper, I think this is the type of motion that's happening. This motion has no significant effect on group size.

I think that Bryan is interested in measuring evidence of a large corkscrew bullet trajectory, where the bullet traces a circular path around the direction of travel, and the radius of the circle is larger than the bullet diameter. This type of motion could cause a group size that increases with range. However, it happens in only rare circumstances.

 

[Topshot]

Bryan,

I have an idea as to what may be causing this for some shooters and it has more to do with poor maths and group measuring method than exterior ballistics.

It seems that a lot of people measure their group size by the overall size of their groups. Others measure their group size by centre to centre of the widest bullet holes.

Now take a shooter that tends to measure by the first method. He has a rifle .308 rifle that shoots a 1/2" group when measured to the outside of the bullet holes at 100 yards and calls it a 1/2 MOA group.

On another day, the shooter goes out and shoots again. This time at 200 yards using the same measuring method the rifle shoots a 3/4" group. The shooter says that the group is less than 1/2 MOA and comes to the conclusion that his rifle shoots smaller groups at 200 yards than a 100 yards.

Can you see anything wrong with his line of thinking? If he used the centre of the bullet holes as the measure point, I think he would not have come to this conclusion.

 

[cohunter14]

I think the people who have reported seeing this are smart enough to know how to measure their group sizes from the center of a bullet hole...

 

[tbrice23]

+1

Sometimes i can't seem to say things in a polite way

 

[Pdvdh]

I think the people who have reported seeing this are smart enough to know how to measure their group sizes from the center of a bullet hole...

Yet as commonly as people report this phenomenon, I have yet to hear of any of them delivering their rifle to Bryan.

 

[cohunter14]

Yet as commonly as people report this phenomenon, I have yet to hear of any of them delivering their rifle to Bryan.

I know...I'm surprised by that. I wish someone would take him up on his offer so Bryan could figure it out.

 

[J E Custom]

I am not a non believer in bullets "Going To Sleep" but in 50+ years of shooting and 0ver 15 years of rifle competition I have never had it happen to me.

Looking back at my match log book I found that on average, the greater the distance the larger the group and the group remained consistently larger as I went out father. I have also shot many odd
shaped groups, and at greater distances they maintained the shame shape but were larger By the MOA shot + a little.

I do believe that Most people will hold tighter at longer distance and that other things can effect
the group size that may Indicate tighter MOA groups at longer distance.

I like to see this type of testing to verifie if this phenomena does exist as well as other Phenomena
that has not been proven.

Thanks Bryan, and keep us posted on your findings.

Interested

J E CUSTOM

 

[trickytune]

I just had a thought and remembered this post after reading another post by Brian about barrel whip and how it can compensate for different velocities. And a thinner barrel has more whip. So can a barrel over compensate so that the lower speed bullets land higher than the higher velocity ones at 100 yards but then at longer range they all seem to match up? Is that even possible?

 

[trickytune]

I ran it through shooter using my 260 rem with an extreme spread of 92fps. If the lowest speed was 2600fps and the barrel compensated .500" higher than the 2692fps round the slow round would impact .500" high at 100m. But both bullets would have the same impact point at 300m. I have looked and seen a test on HSM 168 AMAX match ammo with extreme spread of 94fps. Maybe the ammo being used for testing is too good?

 

[Pdvdh]

The cartridge load, MVs, ESs, and everything else needs to be identical, in order to prove anything about short range moa precision versus long range moa precision. Which is why Bryan is measuring of the precision of the very same fired bullets at both a shorter and a longer distance - concurrently - if I understand his testing setup correctly.

The question is, can bullets disperse non-linearly in a manner that results in improved moa precision at longer ranges, where natural linear dispersion would be expected to display itself in larger (equal at best) moa measurements of precision. Using differing loads for the shorter range precision measurement than for the longer range precision comparison would add a separate reason/explanation for any reduction in moa precision at the longer ranges - such as the different long range load is simply a better, more accurate, more precise load in the firearm than the different short range load was with the different MV.

It's safe to say Brian hasn't received or tested any rifle that displayed non-linear dispersion that improved precision at longer ranges, compared to shorter ranges. Surely he would have posted something.

I can't speak for him, but I doubt Bryan ever expected to receive a rifle, or ever expects to test a rifle, that displays improving precision at longer ranges than at shorter ranges. It shouldn't be possible, from my understanding of the physical sciences, mixed together with a reasonable dose of common sense.

Lots of folks commonly report better precision at long range than at short range. There's some other explanation than bullets that somehow self-guide themselves into more precise groups at long range than at shorter range. There's an optical or some other explanation. Anything other than the bullets seek to plant themselves into a single hole at longer yardages using self-guiding alien technology. Ain't gonna happen...

 

[trickytune]

I disagree but I am not going to argue. If a person buys a rifle from the shop and some factory ammo like the HSM with large spread, then goes to the range and finds his rifle does have non linear dispersion. First we need to find a combination that does this then we can work out why. At the moment there has been nothing to work with.

 

[Pdvdh]

At the moment there has been nothing to work with.

That's because non linear dispersion (in the form of group convergence) has yet to be demonstrated, when the same fired bullets have been measured concurrently at both closer and longer ranges. Anyone that owns such a rilfe, Bryan's stated he's willing to test it and pay for all cost associated with testing. Heck, he's on the verge of offering a reward for such a unicorn...

I'm not arguing. Provided some clarification, and have stated an opinion - as have you. In this specific Thread, Bryan's stated he's not searching for theoretical explanations that could explain the allegations that non linear dispersion exists. He wants a rifle to test with LIVE FIRE, that flat out displays non linear dispersion. He's gone to the end of the rainbow searching for one.
The following quote is from his Post #120:

"Guys,
This thread/challenge is intended to explore the question of IF group convergence happens with LIVE FIRE experiments. I've presented results from several of my tests, and Canadian has posted the results of his test. Other than that and the information presented on past live fire experiments, most of the discussion has been off the intended topic.

I'm open to discussing any means of demonstrating group convergence on my shoot thru target, or someone elses. The theory is interesting, but as far as this thread goes, it's irrelevant until convergence is directly demonstrated as being repeatable.

Maybe I should consider paying a cash reward for anyone who can successfully demonstrate convergence...? That may help keep the discussion focused.

-Bryan"

 

[tbrice23]

I am still reading posts, claims and suggestions claiming " test our bullets further than 100 yards for better results ".
Miraculously no one has been forthcoming in producing a quantifiable example for the world to witness under Mr Litz' plea for some sort of tangible proof.
I honestly don't think that he has had a single volunteer for an example from anyone, besides his own tests with his/AB rifles.

 

[Danehunter]

THE CONVERGENCE/DIVERGENCE VARIABLES;

Some variables were stated above:
1. barrel "whip" or harmonic vibration AND muzzle location (i.e. 7 o'clock, etc.) at time of bullet exiting the muzzle
2. load consistency (many variables here)
3. atmospheric conditions (indoor temp & humidity controlled range being the best choice)
4. barrel stiffness (i.e. resistance to "whip" - achieved through greater barrel mass or specially wrapping barrel in carbon fiber, as with Christensen barrels.

Other variables:
5. rate of twist (best rate for bullet caliber, weight and velocity)
6. radial shock wave & bore diameter expansion timing for bullet exit from muzzle (separate factor from from barrel "whip")

When these variables and others, such as Coriolis effect beyond 1,000 meters, are all accounted for and measured then we can begin testing for convergence and divergence at various ranges.

I for one would not want to be charged with such "accountability" for all these variables. I highly respect those who can test a hypothesis of bullet trajectory convergence/divergence and minimize these and other variables to seek an answer.