Enlighten Me... Strange Difference in Hert. and Port. Ammo

[Bruce J]

I went to the range and was punching some nice holes in paper. I changed magazines and suddenly my groups move about a foot off.

I realized I had different ammo in the new magazine, Portugese, I had been shooting Hertenberger.

I understand there can be a difference, even if its all supposed to be NATO spec.

However, the differences were not just vertrical (twelve inches below), but it also shot about 12 inches to the left! I'm no ballistics expert, but I thought this was strange.

I switched ammo on and off and found this to be consistent.

Enlighten me... I understand and expect some certical varriation, but why the horizontal varriation?

[This message has been edited by Bruce J (edited October 17, 2000).]

[Super B]

When I change from 150 to 165 grainers in my '06 my groups move 6" to the left. Can't advise between the two same bullet weight rounds.

[S.Kargoh]

Different loads can alter the harmonics of the barrel, thus altering the point of impact in any direction.

[GySgt D]

Ditto what Mr. Snail said, but it does sound like that is quite a difference to chalk up to just barrel harmonics.

[Bruce J]

I hadn't thought about the whole harmonics part. That at least gives me a way to think about it.

When I noticed a difference I was shooting my inch FAL equiped with a measley SUIT.

As I began to experiment, I pulled out my CETME, it has a decent scope on it since the sights are worthless.

I found the differnce was even more pronounced in the CETME. Maybe the fluted, shorter barrel has something to do with it. This is where I found the 17 inch diagnal difference in the ammo.

[S.Kargoh]

Well, I'd start by trying to eliminate variables. Use the same magazine with different ammo. Perhaps the different magazines were feeding the rounds in differently (i know it's a stretch, but you want to make sure it really is the ammo that is causing the difference).

HAve someone else shoot the rifle and see if they can duplicate the phenomenon.

Make sure you are resting the rifle in the exact same manner each shot regardless of ammo choice.

I can't think of anything else, but it would help you to eliminate variables by analyzing your setup and taking notes of what you did or did not do. Barring any noticeable difference in routine, you must assume that the ammo simply patterns much more differently than you originally thought. In that case, stock up on one kind and use it exclusively for maximum confidence in your point of impact. You won't have the explanation that your mind craves, but you'll hit your target. http://www.fnfal.com/forums/smile.gif

[Wadman]

Hey Escargo,

Good suggestions. I'll have to file those away for future use should something similar happen to me. I've also got a mix of about four different ammunition labels.