Ballistics Mystery

[JackEllis]

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

Neither have I

[JackEllis]

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.

Agreed. The way I fell into this was test shots with hand loads that landed off the target (~4 inches high) at 100 yards. I realize different ammo will land differently, but 4" didn;t make sense and I wanted to understand why.

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.

I was planning to try something along those lines though I had no idea how much more to shorten the round. Any advice on how short on OAL I can go without causing a problem? It looks like I've got another .05 to the top of the upper groove, which would mean shortening by up to .08.

That differing point of impact is the barrel harmonics or whatever you want to call it.

I need to look into this a little more. It makes more sense than a change on POI caused by higher muzzle velocity but my possibly faulty intuition tells me harmonics or having the barrel whip around would likely result in a bigger spread rather than a consistent difference.

[LynnJr]

A poster stated that faster shots don't always hit higher on the target and that is only caused by Shooter error.

[pennstater]

What is your bench rest like? In other words, how exactly are you holding the rifle? The same, ALL the time? This also works into the equation.
Oh, one last thing; what are your optics?

[JackEllis]

What is your bench rest like? In other words, how exactly are you holding the rifle? The same, ALL the time? This also works into the equation.
Oh, one last thing; what are your optics?

I doubt the bench rest, hold consistency or optics would make the kind of difference I'm seeing since I put three shots using the hand load within a little over an inch of one another (top three shots in the photo). To answer your questions in order, sand bags, consistent sight picture of the inside of the scope reticle, and the scope is a Leupold 2.5-8x33 VX-III.

Shooter, rifle and scope were good enough to bag this:



Today and tomorrow are supposed to be dry so maybe I can get in a little range time to figure this out.

[ar15barrels]

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?

The barrel oscillates up and down as the bullet is going down the barrel.
Ideally, you develop loads so that the bullet leaves at the TOP of it's swing.
If you have a bullet leaving on the up-swing and you continue increasing the charge, it will eventually be leaving in the previous down-swing and that will cause it to go LOWER at short range.

Alternatively, if your bullets were leaving on the down swing and you increase the charge, you could cause them to start leaving on the up-swing.
That would show a much larger movement on target than the velocity would suggest.
This is short-range bullet impacts being effected by barrel harmonics, not velocity.

At LONG ranges, the extra velocity will reduce the drop and the bullets will be landing HIGHER on target.
You won't see the velocity driven elevation changes until you get to a few hundred yards though.

[russ69]

...Shooter, rifle and scope were good enough to bag this:...

The MOA of a game animal is a much looser than a target MOA.

[pacmule]

This thread reminds me I need to go shoot my rifle. I still have some testing to do.

[LynnJr]

When you load ammo at 2200 fps and your chambering is capable of 3000+ fps your bullets will only hit higher on the target from 2200 fps all the way to 3000 fps.
Do a ladder Test and any time you see hits going lower that is Shooter error and not barrel harmonics

[Flouncer]

This thread reminds me I need to go have a stiff drink because of the internet. I still have some testing to do.

Seriously.

[ar15barrels]

any time you see hits going lower that is Shooter error and not barrel harmonics

Not at 50yds.

[maxx03]

Run them thru a chrono and you'll see why.

[LynnJr]

Bullet behaviour doesn't change in small yardage changes like 50 yards.
Convergence takes place around a node due to very small muzzle angle change and a very small velocity variation. The slower shots are in the barrel longer so they leave the muzzle at a steeper angle and converge with the faster rounds.
Barrel harmonics affects the vertical spread of your group.
The bullet is still hitting higher on the target but only groups well near a node.
If the barrels muzzle is moving downward the slower rounds that are in the barrel longer will not converge with the faster rounds and that is why you get big groups.
If you map it out from your lowest velocity to your highest velocity as the velocity increases the rounds will print higher but will only group well near a node.
When you add a tuner to a barrel it will compensate for a larger velocity variation because the mass added to the end of the barrel dampens the harmonics and flattens and widens the node.

[ar15barrels]

Frank?

[killshot44]

Leonard?