New ar-10 piercing primers

[Hatedbysheeple]

Took my new Adams arms .308 out to my dads today to zero my new scope. Was shooting factory federal 168gr Sierra match King. It punctured the primer on 8 out of 10 rounds and cratered the other two, no primer flattening, but the anvil came through the punctures. Went and got a 308 savage bolt gun, 3 rounds through that, no puncture, no primer deformation.

I didn't have any other ammo with me, but I am leaning toward a bad shaped or out of spec firing pin, or an over sized firing pin hole, I will have to wait till tomorrow to get measurements. The gun was also failing to eject but I think that may have to do with the primer issue.

[Schuetzenman]

It could be related to the throating of the chamber. You could be getting pressure spikes if they didn't cut it right. Check headspace though this will not address throat condition. I have an AR I built with a Kreiger match 1 in 7.875" twist barrel that is very touchy with some bullet and powder combos. They really built it for the 80 gr. Sierra MK bullet which is as long as a 147 gr. NATO projectile. Given the .224 diameter it looks like a needle so it is super skinny in the Ogive. 69 Sierra MK's are a lot fatter and they were blowing and piercing primers like crazy. I finally had a 5.56 chamber reamer run in it to open it up to work better with the 69 Smk bullets. Your barrel may be throated for a VLD style of bullet vs. NATO spec bullet profiles or even that 168 gr. match bullet.

I did play around with stoning down a firing pin to help the piercing of primers, it did improve things when I shortened it .010". There is risk, make it too short and you won't have any ignition. I made sure I had a backup Firing Pin before I tried that by the way.

[NAPOTS]

I bought a complete RRA upper with bolt carrier group and it was piercing primers pretty bad, probably about 8/10 like yours. I noticed the firing pin had a tiny burr on the tip, I stoned it just enough to smooth it out and it has worked fine since.

[skorpion]

Yes, replace or file down the firing pin. Next step would be to install a lighter hammer spring if that doesn't work 100%.

Also take a look at the base of the firing pin (the muzzle side) to see if it's mushroomed out or out of spec.

ETA:
Brownells firing pin protrusion gauge. A 'smith may be able to check this for you for cheaper than the cost of the $25 tool. This is for 5.56, though. I'm sure someone out there makes one for a .308 AR, though I couldn't find any during a quickie search.

http://www.brownells.com/gunsmith-to...prod26477.aspx

[l921428x]

Took my new Adams arms .308 out to my dads today to zero my new scope. Was shooting factory federal 168gr Sierra match King. It punctured the primer on 8 out of 10 rounds and cratered the other two, no primer flattening, but the anvil came through the punctures. Went and got a 308 savage bolt gun, 3 rounds through that, no puncture, no primer deformation.

I didn't have any other ammo with me, but I am leaning toward a bad shaped or out of spec firing pin, or an over sized firing pin hole, I will have to wait till tomorrow to get measurements. The gun was also failing to eject but I think that may have to do with the primer issue.

Is fp the right length? Can you mic it to spec?

[Hatedbysheeple]

Is fp the right length? Can you mic it to spec?

I am in Illinois, my mic is in Virginia, will have to do it tomorrow night or monday

[Hatedbysheeple]

Here is an example of the two types of primer damage

[1 Patriot-of-many]

Whatever you do, DON'T file down the firing pin.......an Antigun democrat told me it will go full auto......

[Hatedbysheeple]

Emailed Adams arms this morning, heard back within an hour. They said I had an early production rifle that had some issues with the bolt and firing pin and asked me to mail the rifle back into them to update the components and get it running, they are covering all shipping. So we will see how this goes.

[l921428x]

Well that is good to know. Keep us informed.

[skorpion]

Emailed Adams arms this morning, heard back within an hour. They said I had an early production rifle that had some issues with the bolt and firing pin and asked me to mail the rifle back into them to update the components and get it running, they are covering all shipping. So we will see how this goes.

Sounds like good customer service. Hopefully you get a well-running rifle returned to you.

[Schuetzenman]

Here is an example of the two types of primer damage

Looks like my Kreiger barrels fired shells before I had a more conventional chamber reamer run into it. It could be the Firing Pin hole in the bolt is too large as you mentioned. The radius in the corner of the primer is still there, but that's a lot of primer flow into the FP hole.

[Lightning 351]

Whatever you do, DON'T file down the firing pin.......an Antigun democrat told me it will go full auto......

Lol!!!!!I was going to post that!!!!