This weekend i was running a 14.5 DI carbine length gas system with a surefire FA556 suppressor and at least once a mag experienced a blown primer (Top hatted primer). I though ammo problem first but i experienced issues with 55gr PMC, Lake City M855, IMI M855, Hornady 75gr and black hills 77 gr. When i removed the suppressor the problem was not occurring at the same rate. I’m thinking over pressure but thats as far as I’ve gotten. Any thoughts would be appreciated.
first time running that suppressor?
I’d contact surefire about it…
I would be suspicious about chamber dimension.
Sound to me like you have something a bit tighter than a 5.56 Nato chamber.
I thought it might be the suppressor so i put on a buddys gun and no issues.
Barrel is marked 5.56 and i have not had any issues with military 5.56 loads in the past. do you think the suppressor (and added pressure) just inflamed an existing problem?
I think that the increased fouling in the throat/lead might be exascerbating the issue, and if removing the suppressor made the issue go away I am inclined to believe that it is doind something else as well, though it is a bit counter-intuitive as far as operation goes.
Who is the manufacturer of the barrel? Not all 5.56 marked barrels are actually 5.56 dimension chambers.
+1. If it’s with multiple dif types of ammo, I’d explore the chamber dimensions a little more.
You may want to look for a 5.56NATO chamber reamer by Ned Christiansen at Michiguns. A “5.56 NATO” stamp on the barrel does not always mean a 5.56 NATO chamber, unfortunately. Certain manufacturers have been known to stamp the barrel as 5.56 NATO, but when a chamber reamer was applied, MUCH material was removed.
A 5.56 NATO chamber reamer should basically spin freely if your chamber is already within 5.56 NATO dimensions. If you have closer to a .223 SAAMI chamber, it will drag and you’ll feel it.
It is a goverment profile CMMG with .750 low pro gas block. I have also expecienced more then usally malfunctions in the last month as well. Just not to this extent.
When is the last time you thoroughly cleaned the chamber and bore?
How often (round count) do you normally clean the chamber and bore?
What issues have you seen recently?
I have heard reports of CMMG guns with tight chambers, so it is possible that you are seeing these issues popping up recently due to accumulated fouling in the throat/leade.
I am not saying that this is definately the issue, just trying to help diagnose if this might be a problem, because a good scrubbing is a lot cheaper than any other fix I know.
You might want to have your chamber hit by Ned Christiansen’s 5.56 reamer, but if no one in your area has one you can borrow or rent or have a gunsmiff use, it is kinda cost-prohibitive.
I have personally owned a CMMG gun marked as 5.56NATO that was not. Thanks to them, I spent the better part of a 3-day rifle class shooting a handgun instead…I should probably thank them for all the transition practice. As has been suggested, check the chamber.
about two weeks ago i did a thoroughly clean and used a parts washer too.
any time i shoot the gun I clean it and usally thoroughly.
I have experienced failure to eject a few times, were the spent casing is very tight and i had to hit my stock against the ground to get the round out. I have also experienced failure to eject were the bolt ripped the rim of the casing. I’m starting to think the chamber is the problem.
The chamber does not seem like its fouled up. Is it possible its time for a new barrel?
I know the feeling. I have a couple classes coming up and i’m thinking i’ll just get a new barrel. It’s interesting that i havent had problems till the gun had around 6k through it.
I would seriously recommend considering a new upper. a BCM 14.5" middy w/ appropriate muzzle device would be the bee’s knees. I currently own a 14.5" BCM middy that i received two weeks ago…they shoot as soft as everyone says they do. 
When you start adding up the cost of changing barrels, the current sale on complete uppers at BCM makes that seem a little silly, as the prices virtually equal out.
Dropped primer. Blown makes me think pierced or blown out around it, what you have is I suspect a normal looking primer that did not stay in the case.
The increased cyclic rate suppressed shows possible chamber/pressure issues. Or it may just be overgassed without the silencer and then becomes way overgassed with.
I have come to the conclusion that it is the chamber and the barrel that is at issue. The primes were in fact blown out. My next step is to get a BCM middy upper have it pinned and just use my existing bolt group and upper. Are their any issues with using my old BCG with the new barrel?
I would check the headspace whenever a bolt or barrel is replaced.
It is very difficult for the primer to be blown out without a KB, generally the bolt face holds in it place while there is pressure in the case. If the case head is expanded from excess pressure or has not had time to retract (extracting faster because of the higher cyclic rate with silencer) the primer may drop out when the case is ejected.
You probably have a pressure/chamber issue.
Thanks for the help, I’m going to order a complete upper w/ bolt and call it a day.
Not sure how many rounds are through the barrel or how long you have had it. But, I would at least contact CMMG and let them know the issues you have or had. Especially since their website claims that they are milspec barrels.
I believe that one of their reps even posted here on M4C. I would look for that post.
I find it especially interesting that their website states any use of steel case ammunition will void their warranty. Why is that? My AR’s are all able to shoot Hornady steel case 55gr. TAP without problems.