I am the second owner of a CMMG AR-15 Model MOD4SA
Over the past 100 rounds, I have had a number of problems mostly dealing with extraction, but also with blowing primers resulting in pieces that would get lodged in the Bolt assembly. The extraction issues were solved , but the primer blowing issues still remain despite replacing the firing pin with a new one from Bravo Company.

At the range today, My instructor brought his AR and we compared spent brass. His brass appears normal (including using some of my ammunition (federal XM193) My brass showed a ridge around the depression made by the firing pin on all primers except those that were completely blown through (see attached photos)

Any idea what is happening? Suggestions on repairs?

Normal Spent brass:
http://i27.photobucket.com/albums/c200/radioflyer1986/misc/Arms/normalbrass_zpsce30e72a.jpg

My brass:
http://i27.photobucket.com/albums/c200/radioflyer1986/misc/Arms/mybrass_zpsabc1163a.jpg

Worst of my brass today: light strike, heavy strike punchthrough and blowout
http://i27.photobucket.com/albums/c200/radioflyer1986/misc/Arms/Reallybadbrass_zpsa8c2f73c.jpg

My bolt:
http://i27.photobucket.com/albums/c200/radioflyer1986/misc/Arms/IMAG0466_zps770eeb3e.jpg

http://i27.photobucket.com/albums/c200/radioflyer1986/misc/Arms/IMAG0467_zpsc24464b9.jpg

I think Dano has it for you.  Most of this looks like straightforward over-pressure loads with a mis match in powder, case or bullet.  Be sure you are using mid range loads of the right powder to start and work up, looking for signs of over-pressure along the way.

Do also check the headspace; tight but closeable headspace can do this by creating an overpressure situation.  Not likely, but possible.
Let us know if our suggestions are on beam.

I had a CMMG and was experiencing blown primers with any type of 5.56 ammo.  This was giving me all kinds of fire control problems, as well as well as failure to return to battery issues with the primers getting stuck in the most inconvenient places. The .223 seemed to be ok with no problems.  I tried a heavier buffer, which did not help.  I sent it back to CMMG where they re-cut the chamber.  After that ALL problems ended.  I would recommend giving them a call.  They will make it right and save you lots of headache.

Hey guys I also have CMMG.  Its is chambered in the 300 Black out.  I have not had any blown primers yet.  I guess i need to knock on wood.  But here is the problem I'm facing.  My Blackout will shoot my reloads perfectly fine, but when I try to shoot factory Remington ammo it will not.  I called Justin at CMMG (Tech Engineer) he said that they have had some issues with the Remington brand of ammo.  He suggested a Gorilla brand of ammo and they have no issues.  I think I know what the problem is with the  Remington ammo, the primer is set just below the surface of the casing.  My reloads are set flush with the casing.  It seems like the firing pin is just not long enough to reach the primer on the Factory Remington Ammo.

I asked Justin exactly what is the spec, dimension, length of the pin and also the length of the bolt.  He said he could not give that information out because of liability issues.  My question is could you not take a thousand or two off of the back of the bolt and achieve the same results as sanding the firing pin?  My thoughts are if you take to much metal off of either the bolt or the pin you could end up with blown primers?

In this post also one of you gave the dimension the pin protruding out of the end of the bolt face.  Im sure you use a caliper, but how do you use the caliper to measure the distance?

Also for a heads up Justin also said that they no longer void a warranty for shooting reloads.  Unless you really do something stupid.

Anyone have the exact Factory Spec length of the pin and bolt, or know how to obtain it?  One food for thought is the 300 AAC Blackout uses the same pin and bolt as the 223 rem.  The Blackout pin measures 3.279, and the bolt measures 2.801. The DPMS 223 Remington pin is 3.276 and the bolt is 2.799.  I know this is long, sorry.

Any thoughts guys I would appreciate it.

Hey guys sorry, Dano523 explained how to use the caliper to measure the pin protrusion distance.  But If anyone has the spec of the pin and bolt I would really appreciate it if you could post it here.  Thanks.

Thanks Danno, I inspected the back of my bolt and I did have a few small burrs, I removed them and now FP is at 0.33, I haven't had a chance to get to the range yet and see how the AR reacts with the Remington factory ammo.  Provided I get no misfires i'll leave it at that.  If i still get misfires i'll adjust the pin to 0.34 and see what i get.

Thanks a lot for your help.  You are spot on with how to correct this problem.