Ballistics Mystery

[thegiff]

If it is a hunting rifle with a thin barrel, then the harmonics can be huge. I helped a friend a while back with a 30-06, and the loads were about 5 inches up and an inch to the right apart between factory and reloads at 100 yards. but both groups were tight. Was weird to shoot them alternately for a few shots, one in the bull, one high and right, one in the bull and so on.

[JackEllis]

I helped a friend a while back with a 30-06, and the loads were about 5 inches up and an inch to the right apart between factory and reloads at 100 yards. but both groups were tight. Was weird to shoot them alternately for a few shots, one in the bull, one high and right, one in the bull and so on.

I feel a little better now, but it's just plain weird that the hand load shoots three inches higher than the factory load at 50 yards wen I was expecting no more than perhaps a one inch difference. The reason I did this test at 50 was because our initial tests at 100 were hitting above the target.



The three holes near the bullseye are from hand loads (155 gr GMX) that the loading manual says should exit the muzzle at 2800 FPS. The hole at the bottom, also the aim point, is a Wolf (145 gr) that should exit at around 2910 fps. The hand loads are consistent enough considering the skill of the shooter(me) , even with sandbags.

Thanks for all the responses. I'm not sure the mystery is cleared up but it's time to move on.

[LynnJr]

Jack
If you had 10 different weights of factory ammo you would find that 6 or 7 would group in the same area and 3-4 would be outliers.
3 inches at 50 yards is a huge variation. I would chronograph the load and I would thoroughly clean that barrel.
Usually the outliers will be an inch or two at 100 yards so 3+ inches at 50 yards would only be expected from lathe turned solids that are very long or a tighter than normal neck tension associated more with fitted necks and no additional clearance.

[DesertWalker]

New to ballistics physics

OK, I am totally confused. Given the same load & conditions, wouldn't more powder in the cartridge equal more velocity of the projectile, and thus less time for the projectile to fall, resulting in a higher hit on the target?

Or am I wrongly disregarding the trajectory?

Thanks..

[LynnJr]

You are correct. If all else remains the same and velocity goes up so will the bullets impact.
Earlier in the post they were talking about weak loads versus warmer loads and several different bullet weights.

[Mesa Defense]

Barrel Harmonics play a large part as well.

[Mesa Defense]

If your interested in internal ballistics, get a copy of Quickload. Great software that will keep you entertained for hours

[btm]

You are correct. If all else remains the same and velocity goes up so will the bullets impact.
Earlier in the post they were talking about weak loads versus warmer loads and several different bullet weights.

Only if you are shooting from a massive machine rest that can't move. You are ignoring the departure angle.

[LynnJr]

No I am not ignoring anything.
If you take 50 random shots your highest velocity rounds will always hit higher on the target.
Shooter error is what gives you the wild and unexplained shots.
This can be confirmed using any ballistic calculator.

[JackEllis]

I don't have a chronograph and I'm not sure I want to go that far down the rabbit hole right now. I'd still like to sort out the mystery but I'm more interested finding out how well the hand loads group compared with factory loads . Never had two bullet holes touch before from the bench except when shooting a .22LR. Could be a fluke.

The barrel had about 8 rounds through it since the last cleaning when I shot that test. In fact, the sequence of shots was, 2 GMX loads, Wolf load, GMX load. I have the GMX bullet seated to a very few thousandths below the bottom of the top groove (canneulure?). COAL is about .02 shy of the maximum allowable according to my reloading manual, and about .015 longer than the Wolf and Remington rounds.

When we get a break in the weather I'm going to repeat the experiment with three or four different loads at 100 yards: GMX 150 grain hand load as above, GMX seated to the top of the top groove, Wolf 145 grain factory ammo, and the Remington Core Lokt 150 grain factory load. And be a lot more careful about how I set it up.

Thanks for the additional responses. As my wife could say, this has turned into an interesting science experiment.

[mcisniper]

Books, calculators and the internet are good resources, but reloading, just like performance engine building, and long-range shooting, is an art form. Maybe a dark art, but still an art form.

[russ69]

...Thanks for the additional responses. As my wife could say, this has turned into an interesting science experiment.

Short form: Different ammo shoots to different points of impact. The only thing you need to do is zero for the ammo you are using. You can not have one zero for two different loads, well not within my expectation of impact point.

[AFTII]

No I am not ignoring anything.
If you take 50 random shots your highest velocity rounds will always hit higher on the target.
Shooter error is what gives you the wild and unexplained shots.
This can be confirmed using any ballistic calculator.

What is this shooter error you are talking about? I don't think I've ever experienced that.

[LynnJr]

Jack
I just looked that bullet up and it is a solid copper bullet.
There is no mysterious ballistics taking place that is exactly what happens with those bullets.
On your seating depth you will most likely find best accuracy with a lot of jump. You said you were 20 thousandth off I would start at 0.050 off and go shorter on OAL from there.

[Flouncer]

There is not enough velocity in that load to make a difference that big at 50 yards. No way. Nonsense. Use a reloading manual and a chronograph. That differing point of impact is the barrel harmonics or whatever you want to call it.