Applied Ballistics 'Shoot Thru Target' Challenge

[BryanLitz]

Thanks again for the interest and encouragement guys.

Roy, If you get a rifle doing this repeatedly, you can ship it and I'll be happy to test it on the shoot thru target. Thanks for the offer. It's certainly more convenient to ship a rifle than travel from Idaho.

KYpatriot, We're on the same page. The point here is to explore potential problems so they can be understood and solved weather it's a flight mechanics or optical issue doesn't really matter to me, what matters is learning the true reality.

bruce, I can assure you that I was carefully adjusting the parallax before firing each group. Since Parallax is one of the known potential mechanisms which would explain this phenomena, I wanted to be sure to eliminate it from this test.

Next thing I plan to do is try and repeat the result I got last time. Then I'll experiment with smaller aimpoints at 100 yards, so they're proportional to the size of the 300 yard aim points. In other words, rather than use 1" circles at both ranges, I'll use .33" circles at 100 yards and keep the 1" circles at 300 yards.

I'll then design further testing based on those results.

But the very first thing to do is verify the last result before putting too much stock in it.

Hopefully the effect can be seen with smaller calibers; the .375 CheyTac burns 130 grains of Retumbo per shot, and to line up with the shoot-thru target I have to shoot from my bench inside the lab (metal walls and roof, ouch!)!

I'll keep you guys posted. In the mean time have a happy Thanksgiving.

-Bryan

 

[royinidaho]

Going to have to wait till the cows are moved out of my shooting range. That'll happen when the snow gets deep. It's gone now.

I'm going to attempt to arrange a 100 yard target such that the bottom of is will cut across the center of the 400 yard aiming point. Lay of the land prevents this using 100 and 300 yard targets.

The idea will be to hit both the 100 and 400 yard targets with each shot. Then use the 100 yard aiming point then the 400 yard aiming point.

We'll see if I can bring this off...

 

[DocB]

I've actually experienced this when I was shooting with the AMU at Ft. Hood. We thought we just had a really good rifle! We didn't mess with it because we didn't want to mess up a good thing.

So I've been intently following what everyone has written, gone back to Brian's book and articles on sleeping and epicyclic swerve trying to put all this together and I'm getting there.

There's just one thing that's slowing me down and that's how do you configure a 'shoot through' target? I can't quite visualize how it's set up and your aiming points on the target and reticle. Hopefully someone can guide my increasingly feeble brain thru this.

Thanks to everyone for an enlightening and educational thread.

DocB

Animo et Fide "Courage and Faith"

 

[dkhunt14]

I don't believe it is parallax or aiming better that causes it. If you take a 90 pound 1000 yard heavy gun that runs on rails and tracks 100 percent. You do not move the gun so that takes aiming and parallax out of the picture. A 100 pound Dasher with a brake doesn't move. I make all my test targets with a cross drawn on the paper with a small dot in the middle. I line up the crosshairs on the lines so that also takes aiming finer at a distance out of the picture. Then you have the machine rest guns like they shoot in PPC or in the Sierra bullets tunnel. A ballistician from Sierra told me that there 6.5 142 grain bullet was their fastest settling bullet. He also said some were just barely or not quite settled at 300 in the tunnel. I bet high speed photography would show this. I know this one match shooter that said he had this old guy that would take him to this spot at a certain time of day and he would shoot uphill and the guy would tell him if the load would work. He did this a couple of times and it always shoot good when the guy told him that load would work. One day he asked him what he saw or was looking at. The old guy told him he could see the end of the bullet and tell if it was corkscrewing or not. Matt

 

[Mikecr]

So to the point, does the 90lb gun shoot tighter MOA with distant shooting over near shooting?

 

[zfastmalibu]

Bryan,
Here is some reading for you.
Using barrel vibrations to tune a barrel
Alex Wheeler

 

[dkhunt14]

So to the point, does the 90lb gun shoot tighter MOA with distant shooting over near shooting?

Yes a lot of times the MOA is smaller at 400 then 100. Most of my match guns will shoot in the 1/2 to 3/4 inch range and at 400 where I do most of my testing will shoot 1 to 1 1/4 inches. It does this on a fairly consistent basis. I now do most of my testing at 1000 because I have seen good loads fall apart when shot at 100 or 400. Ask any 1000 yard shooter and most will tell you that. My first post was to show that i don't believe it to be Parallax or finer aiming. I watched the PPC shooters shoot there rail guns at nationals the other year when it was close to my house. They didn't touch the gun once they started a string. 10 shots in 10 seconds or so and most were done. Matt

 

[royinidaho]

I don't believe it is parallax or aiming better that causes it. If you take a 90 pound 1000 yard heavy gun that runs on rails and tracks 100 percent. You do not move the gun so that takes aiming and parallax out of the picture. A 100 pound Dasher with a brake doesn't move. I make all my test targets with a cross drawn on the paper with a small dot in the middle. I line up the crosshairs on the lines so that also takes aiming finer at a distance out of the picture. Then you have the machine rest guns like they shoot in PPC or in the Sierra bullets tunnel. A ballistician from Sierra told me that there 6.5 142 grain bullet was their fastest settling bullet. He also said some were just barely or not quite settled at 300 in the tunnel. I bet high speed photography would show this. I know this one match shooter that said he had this old guy that would take him to this spot at a certain time of day and he would shoot uphill and the guy would tell him if the load would work. He did this a couple of times and it always shoot good when the guy told him that load would work. One day he asked him what he saw or was looking at. The old guy told him he could see the end of the bullet and tell if it was corkscrewing or not. Matt

Darn, this shoots down my incentive to fab up a machine rear for this project.

Still may do it though.

Considering Matt's post what is going to be the fastest means to the end?

 

[justgoto]

Bryan,
Here is some reading for you.
Using barrel vibrations to tune a barrel
Alex Wheeler

"Barrel harmonics" and bullets "going to sleep" are two completely different issues.

 

[Mikecr]

Well dkhunt14, Bryan is looking for someone to demonstrate smaller moa at distance over near.
Maybe you can help with one of them guns you don't even aim with.

 

[KYpatriot]

Yes a lot of times the MOA is smaller at 400 then 100. Most of my match guns will shoot in the 1/2 to 3/4 inch range and at 400 where I do most of my testing will shoot 1 to 1 1/4 inches. It does this on a fairly consistent basis. I now do most of my testing at 1000 because I have seen good loads fall apart when shot at 100 or 400. Ask any 1000 yard shooter and most will tell you that. My first post was to show that i don't believe it to be Parallax or finer aiming. I watched the PPC shooters shoot there rail guns at nationals the other year when it was close to my house. They didn't touch the gun once they started a string. 10 shots in 10 seconds or so and most were done. Matt

Well, the way to know for sure is shoot one of these rifles that exhibits this shrinking moa grouping behavior using Bryan's pass thru target test. Lots of people say they see it, but until it is demonstrably proven by recording group sizes at two different ranges in one firing I still believe it is something optical or shooter related.

One of these rail guns would be perfect for it...extreme repeatable precision and the weight and tracking reducing shooter influence. For instance if we saw such a rifle in a disciplined, controlled test print a .75 inch hundred yard group and the very same bullets grouped an inch at 300 that would likely lead us in the direction that there is an external ballistics reason, especially if it did the same thing with a different parallax setting, a fixed power scope, or no scope at all.

Most of the time I hear of this phenomenon from shooters flinging the heavies...300gr .338s or the various 375 and 408 cheytac rounds. It comes up enough that I know that good shooters are observing the effect, I just wonder about why it happens. It would be cool if someone with a rifle that does this a lot would run this test and help figure it out. Might lead to a great understanding of external ballistics, better optics construction, shooter technique or a combo of those.

 

[zfastmalibu]

"Barrel harmonics" and bullets "going to sleep" are two completely different issues.

Did you read the article?
The reason for larger moa groups (vertically) at shorter range is explained in the article and Varmint Al's web site.
P.S. barrel harmonics and bullets going to sleep are not two different things, ever notice how you can tune the size of your bullet holes with the load?

 

[royinidaho]

ever notice how you can tune the size of your bullet holes with the load?

Nope.

Only when bullets become unstable and tumble. Such as a 75 gr 224 in a 12 twist.
No amount of load tuning had any noticeable affect.

 

[zfastmalibu]

Roy, ask a Benchrest shooter and they will tell you. Some guys actually tune just for the smallest hole...
Start at the 6 minute mark.