Extreme variation in point of impact from one ammo to another

[eric75]

I bought a bag of cheap gun show ammo for my .308 H&R Ultra Hunter thinking it would be good for plinking and for the preliminary phases of sighting in. It is marked ".308 win 168gr boat tail hollow point match."

After sighting in and getting about 3" groups with the cheap stuff at 100 yards. I took it back to the 50 yard range and discovered that the point of impact for my hunting ammo (Winchester 180gr Power Point) is about 6 inches lower than the for the poorly marked gun show ammo.

This has me confused. I expect them to be a little bit different (maybe an inch), but at 50 yards .308 can be considered to be a pretty flat shooter. The only theory I can come up with is that the mystery ammo is a really hot load that causes some dramatic barrel whipping harmonics. Even this seems far-fetched too me, because it's a 20" barrel with a heavy profile. It is probably not the scope or mount, because the gun continues to shoot about 1.5 MOA with my hunting ammo. Except for the fear that this ammo is dangerously over pressure, I am tempted to make some more controlled observations.

Do any of you have some thoughts or similar experiences? Or am I just going crazy?

[Tim R]

A slower moving bullet will hit higher with longer barrel time during recoil. I don't know of any 2 loads which can be zeroed the same, including pistol ammo. This is why once I find my load I stay with it. It goes so far the same manf. ammo but with a different lot number may or may not hit the same point of aim. I've even seen a different lot of powder put bullets in a different place on the target.

[Jimro]

Eric,

You are not going crazy. The cheap ammo probably uses a lighter bullet, and it is probably fmj ball. Probably military surplus of some sort.

If you can tell us what the headstamp on the cheap ammo is, we can probably tell you something about it. If you bought someones handloads then all bets are off.

Jimro

[eric75]

The headstamp reads, "F C 308 WIN"

They look to new to be surplus, besides they are hollowpoints. I'm assuming they are handloads.

I expect the drop from the bore axis at 50 yards is about .75" for a "normal" .308. Even a theoretical bullet with no drop would be only .75" high relative to the other ammo.

By the way there was no sign of tipping or instability in the punch marks.

[kozak6]

You're pretty brave to shoot gunshow handloads :D.

If it truly is a handload, all bets are off.

Who knows what it really is?

[Al Thompson]

Eric, that's not that unusual at all. There are lots of variables with ammo, so your results are not far fetched. Buddy's .308 was a six inch pattern producer with any 150 or 165 grain bullets, a solid sub-moa rifle with 180 grain bullets. :)

Sounds like yours is a bit tempermental, but - you have your hunting ammo sorted out, so just adjust the sights to your hunting ammo and use the gunshow stuff for practice. One way to do that is just off-set your scoring point to POI and keep the same aiming point for practice. :cool: