AR10 started popping primers

[Zak Smith]

I was prepping my AR10 for a match coming up this weekend by chonoing and zeroing a new batch of 168gr Black Hills ammo I just picked up.

I noticed that the velocity variation was pretty high - normally I get about 2620fps from a 168gr load, but I was getting readings as high as 2800+ fps. If everything else were normal and accuracy was good, I'd write this off to my chrono acting up. But after 20-30 rounds, I found several cases with blown primers in the pile of empties and stopped shooting. To my knowledge, this has never happened before with this rifle, shooting 175gr BH, 168gr BH, Fed GMM 168gr, or my 125gr BT handloads.

I hadn't cleaned the barrel real well in about 500-600 rounds, but it didn't look like there was much copper fouling in there.

I gave it a good cleaning with CR10, and I bought some new BH 175gr and FGMM 168gr to try this afternoon.

Any ideas what's going on?

-z

[Huck]

Possibly a bad run of ammo or temp sensitive powder. I have a load for a 300 mag that uses winchester powder that is a crack monkey with temperature swings. It shoots great at around 40-50 degrees but gets crazy at 80. Yes, I am looking for a new powder for it.

[uscbigdawg]

Zak,

If they were handloads, I'd say check your powder charge. Seeing that they are BH ammo, I would chalk it up to a bad lot, but definitely check it out. Take a known load (i.e. your handloads) and run that over the chrono as well as check for pressure signs. Do this after THOROUGHLY cleaning the rifle. If all works well, try the BH again and see what happens.

Huck,

If you're not using it already, IMR 4350 in 300 WM is good.

Rich

[Zak Smith]

Just got back from the range. As I said, I gave the barrel a good cleaning with CR10, and cleaned out the action and b.c.a.

With the Fed GMM 168gr, no pressure signs, no weird velocity variation. S.D. was about 15fps. Groups were about 2x as good (0.6 MOA) as I ever got with the BH, so I'm just going to switch to the Federal.

I shot some new 175gr BH. Velocity variation was about the same as the Fed, but the accuracy was about 2x worse.

Nothing strange with my 125gr handloads.

I didn't shoot any more of the posssibly-faulty BH 168gr ammo. I'll give them a call tomorrow.

-z