6mm creed AR and pierced primers

[stagpanther]

In response to another thread about the 6mm creed in a ruger American I decided to dig my AR build in 6 creed form the back of the safe where it was collecting dust and put a few rounds through her few days ago--also wanted to test a new projectile and powder combination using 108 eldx's and 4000MR powder.

For some reason the gun had intermittent failures to cycle and well before I reached Hornady's max charge I started getting pierced primers and smoke oozing from the receiver--I know how to take a hint and stopped shooting well before completing the ladder.

I got home and checked the fired case dimensions and didn't see any signs of expansion/flow in either the case body or primer cup. Hmmm--maybe wasn't a pressure warning after all. I had recently put a new nitride bolt carrier group in--so next thing I did was take a look at it--turns out there was a sharp edge on the firing pin nose. The carrier had some brass dust on the bottom of it--but other than that I didn't see brass shavings in the chamber or the upper--so my conclusion was the bolt was failing to strip the cartridge and dragging over the top of the cartridge in the magazine for some reason. After stoning the nose of the firing pin down and replacing the charging handle I loaded up the upper end charges and let them rip this afternoon. I was mostly looking to see if the gun worked properly--which it did, everything operated as it should with no issues, and the rest of the charge ladder went off without a hitch or any abnormal signs.



Because the conditions were inconsistent for the whole ladder test I'll do it over--plus it was blasting 25 to 35 winds when I was shooting today, though I still got some promising results. Despite reading that the 1:8 twist wouldn't be adequate to stabilize the 108 gr bullet--it appears that the odin barrel has no problems with that. Here's 42.7 grs of 4000MR, all 4 shots at 100.



The next charge up was 42.9 grs--which was looking really good until I pulled the inevitable flier.




That load obviously bares a second look at.

[HiBC]

I've seen pierced primers with an AR-10 because someone inadvertently used large pistol primers.
I'm not saying that is your problem, it might be something to verify.

[stagpanther]

I've seen pierced primers with an AR-10 because someone inadvertently used large pistol primers.
I'm not saying that is your problem, it might be something to verify.

I've done even dumber things than that--but in this case no, I used fed LR primers which I also double-checked for proper seating depth. I think the sharp pin nose was enough to pierce the primer as well as a slightly bent charging handle cause issues with the path of the carrier in the receiver and cycling issues.

PS--I also know about fed's rep for thin wall easily pierced designs--but I've been using them for years on both 6.5 and 6 creeds with no problems.

[bfoosh006]

Out of curiosity, what is the firing pin diameter ?

And fit in the bolt ?

Just curious.

[Rimfire5]

I had problems with high pressure signs on my bolt action 6.5 that turned out to be a tight barrel chamber on a precision barrel. One of the signs was the primers being pushed back into the bolt face. With an AR, that can lead to punctured primers and smoke, especially if the primers are soft. Once the chamber was reamed out a couple of thousands, the problem went away with no change in accuracy.

As for primers, on my ARs, I use CCI primers because they are harder than Federal primers. Of course, a sharp firing pin could have been the cause of all of the problem, but if the primers are soft, there is more chance to puncture them.

[stagpanther]

Everything is good and functioning normally--under a magnifying glass I could see there was an irregular edge on the nose of the firing pin which I stoned down. The charging handle--a cheapo (yeah, I know, you get what you pay for) has a very slight bend in it; so I replaced it with a new one.