Gunsmithing AR10 deep primer punches

[EastCOYotes]

Maybe a noob question so apologies in advance.

I’ve got an AR-10 chambered in 7mm-08 that was bought new by me and only has around 200 rounds through it. Always the same factory Remington ammo, has always shot good.

My last time out shooting I noticed much of the spent brass had deep punches in the primers, and some of the primers blew out entirely. After breaking the gun down there was actually a piece of primer stuck on the firing pin.

Should I just clean the gun and go back to shooting or do I have bigger issues to worry about? Maybe bad box of ammo, bad job cleaning from the time before, or bigger issues?

 

[GH41]

AR rifles do not have a spring on the firing pin. The pin floats. They were designed to use with mil spec ammunition that uses a harder primer. Soft primers may be part of your deep indentation problem. Also check if the firing pin protrusion is in spec. Spitting primers is probably not related to the soft primer issue. Are there any signs of excessive pressure? Are the primers flat?

 

[EastCOYotes]

AR rifles do not have a spring on the firing pin. The pin floats. They were designed to use with mil spec ammunition that uses a harder primer. Soft primers may be part of your deep indentation problem. Also check if the firing pin protrusion is in spec. Spitting primers is probably not related to the soft primer issue. Are there any signs of excessive pressure? Are the primers flat?

I'll need to find the brass and check them. I think there were some that were flattened though, showing signs of excessive pressure. The strange thing was that other boxes of spent brass I had shot looked fine. Not match quality ammo by any means but still the same stuff (Remington Express 7mm-08, 140 Gr Core-Lokt)

Do I need a special gauge to check my firing pin protrusion or are there any other tricks to doing it?

 

[DAVETOOLEY]

If this just started after 200 rounds your problem is probably self inflicted. If you haven't cleaned the rifle then your problem is carbon and copper build up. A slow through cleaning is in order.

 

[EastCOYotes]

If this just started after 200 rounds your problem is probably self inflicted. If you haven't cleaned the rifle then your problem is carbon and copper build up. A slow through cleaning is in order.

I've cleaned it thoroughly since this issue, but haven't taken it back out to shoot yet. Would you recommend shooting it now that it's good and clean and seeing if the problem continues?

 

[DAVETOOLEY]

I've cleaned it thoroughly since this issue, but haven't taken it back out to shoot yet. Would you recommend shooting it now that it's good and clean and seeing if the problem continues?

I would. Just remember getting carbon out takes chemicals, time and a good brass brush. Soak, stroke, patch out and start over again. Even then you may need to use abrasives.
Just for the hell of it take a snug fitting patch and push it to the muzzle. Then pull it back towards the chamber. Pay attention to the amount of force it takes to pull the cleaning rod as you approach the throat. Many times resistance increase from either carbon build up and/or heat checking.

 

[GH41]

Dave, is there a chemical that actually dissolves carbon or does it just flush what you are abradeing with the brush?

 

[spife7980]

Dave, is there a chemical that actually dissolves carbon or does it just flush what you are abradeing with the brush?

Boretech carbon remover works well. I left my silencer soaking in it for a week (only meant for a day but forgot about it), the majority of the carbon buildup got puffy and wiped off with my finger.

 

[EastCOYotes]

Boretech carbon remover works well. I left my silencer soaking in it for a week (only meant for a day but forgot about it), the majority of the carbon buildup got puffy and wiped off with my finger.

Speaking of soaking a silencer in solvent... Do you think that would work on a silencer that can't be disassembled (like a Thunderbeast Arms one). Then spraying it out with an aerosol can of guns scrubber or other alcohol to try to wash all the broken down carbon out?

Derailing my own post there a bit. I will make sure my 7mm-08 is good and clean and take it out shooting again and see if the primer issue continues.

 

[spife7980]

Speaking of soaking a silencer in solvent... Do you think that would work on a silencer that can't be disassembled (like a Thunderbeast Arms one). Then spraying it out with an aerosol can of guns scrubber or other alcohol to try to wash all the broken down carbon out?

Derailing my own post there a bit. I will make sure my 7mm-08 is good and clean and take it out shooting again and see if the primer issue continues.

The one I was talking about was an omega so not one meant for breaking down like a rimfire or pistol. After the soak and getting all I could out with my finger and pick I flushed it with a hose for a bit and then shot the air compressor through it to dry and blow out any loose mess remaining.

 

[Kiba]

AR rifles do not have a spring on the firing pin. The pin floats.

Not totally correct... While DPMS pattern AR-10s do not have a firing pin spring, Armalite AR-10 rifles do have a firing pin return spring. The OP didn't state if his rifle was Armalite or DPMS pattern.

Also of note, Armalite uses a small diameter firing pin (0.062") that is much less prone to cratering and piercing primers compared to the DPMS firing pin (0.078".) Hence why several manufacturers came out with "high pressure" small firing pin bolts for the DPMS-pattern AR-10's that liked to pierce primers when chambered in .260 or 6.5CM while Armalite AR-10's didn't have the same problems.

I don't have my Armalite anymore, but here's a pic from Google...

 

[El Viejo]

Not totally correct... While DPMS pattern AR-10s do not have a firing pin spring, Armalite AR-10 rifles do have a firing pin return spring. The OP didn't state if his rifle was Armalite or DPMS pattern.

Also of note, Armalite uses a small diameter firing pin (0.062") that is much less prone to cratering and piercing primers compared to the DPMS firing pin (0.078".) Hence why several manufacturers came out with "high pressure" small firing pin bolts for the DPMS-pattern AR-10's that liked to pierce primers when chambered in .260 or 6.5CM while Armalite AR-10's didn't have the same problems.

I don't have my Armalite anymore, but here's a pic from Google...

View attachment 7058364

Do you remember any of the mfrs with "high pressure" bolts / firing pins? I definitely have the problem with my Aero 6.5.

 

[Zak Smith]

JP Enterprises makes one

 

[El Viejo]

JP Enterprises makes one

Thanks. They have two slightly different options. A little pricey but a whole lot better than having pierced primer junk running through my gun which has runs a 6.5 TBAC suppressor since I put it together.

 

[Kiba]

Do you remember any of the mfrs with "high pressure" bolts / firing pins? I definitely have the problem with my Aero 6.5.

Been a while since I've had to swap parts on any of my ARs, but for DPMS pattern AR-10s I know JP makes a high pressure bolt with a small diameter firing pin and I believe Rubber City Armory does also. There may be other companies now offering DPMS pattern AR10 bolts with small diameter firing pins, but I haven't gone searching for them for several years and I'm not sure of current offerings.

 

[mi650]

This was a LaRue rifle with a firing pin spring.

And to Federals credit, they sent me a check for full retail + tax. May have changed since then, but I was told they don't make any .260 ammo suitable for ARs.

 

[El Viejo]

I did my first large frame build a couple of months ago. When I worked up initial loads for a 6.5 CM with aero upper and bcg, I kept getting pierced or cratered primers. My bad assumption was that these were signs of excess pressure so I kept reducing the H4350 powder charge. In effect, I have done a whole ladder for the wrong reason.

The current Hornady manual under the 6 ARC section provides a separate pages for gas vs bolt guns. Do we need that for typical LR308 calibers like .260, 7-08, and 6.5 CM with a reminder on every page to get a "high pressure" bolt meaning .062 diameter and lighter weight firing pin?

 

[LRI]

Speaking of soaking a silencer in solvent... Do you think that would work on a silencer that can't be disassembled (like a Thunderbeast Arms one). Then spraying it out with an aerosol can of guns scrubber or other alcohol to try to wash all the broken down carbon out?

Derailing my own post there a bit. I will make sure my 7mm-08 is good and clean and take it out shooting again and see if the primer issue continues.

You might try this: Boil it in undiluted Prestone antifreeze. seriously.

Years ago, I played in the RC airplane pylon racing thing. (There are cheaper ways to dig a hole in the ground) lol.

The engines use a glow fuel full of castor (bean) oil. The stuff cokes onto the exhaust and is about like DLC to try and remove. It's a hot mess. A guy always showed up with pristine-looking stuff, and he shared that secret with me one day. It works. The other nice thing about it your not stuffing a charcoal canister (what a suppressor basically turns into when its dirty) full of flammable solvents. (smile, wait for flash)

Hot plate, an old soup pot, and a gallon of the green slimy stuff. Have fun!