I had some issues yesterday that I don’t understand. Would appreciate any help in getting it sorted out. I’m real bad about diagnosing malfunctions in the moment since I usually just go into immediate action but some of what I recall seems very odd.
Barrel: 12.5 Criterion Core
BCG: Geissele REBCG
Ammo: 56gr 5.56 MEN
Mags: multiple Gen M3 PMAGs and USGI
Buffer: A5 w/ standard rifle spring
Can: KAC 5.56 QDC
Upper’s total round count: 399
The upper was pretty new with only 204 non-suppressed rounds on it before the class. Those rounds were a mixture of cheap brass cases .223 so this was my first time with the MEN in this gun. The malfunctions started towards the end of the day after about 120 rounds. I kept the can on until I started having issues.
First malfunctions were failures to feed from three different mags. It didn’t look super dirty but I initially assumed that was the issue since I had a can so I just added lube and kept going. Then I had a mixture of blown primers and rounds stuck in the chamber. The first primer lodged itself in between a lug in the barrel extension and the case’s rim, so that the round could not be fully chambered. I had to use a knife to pry it out. I then removed the suppressor and within the next mag or two, had another blown primer. I don’t remember the exact reason but the gun just felt weird when cycling so I stopped shooting and looked. The primer was in between the bolt and bolt catch, stopping the BCG basically at the rear of the cycle. This primer was dislodged by pulling the CH back.
The last was an unfired round in the chamber. I don’t remember why I stopped shooting or what even tipped me off about it, but for some reason, the bolt was locked back (I very well may have dropped the mag and locked it to the rear). I do know that I glanced into the chamber and was very surprised to see a round fully seated with no mark on the primer. I let the bolt go (don’t remember if I did this gently or just dropped the bolt catch), pretty sure I pulled the CH with nothing and then dropped the CH and again pulled it and this time the round was extracted.
I know blown primers can be a sign of over gassing but I had the barrel gauged before JT @ RAW assembled it and think it was .068 which seems reasonable. I know MEN is supposed to be hot and based on estimated velocity yesterday, it was, but am surprised by the mix of blown primers and failures to feed.
Expect a suppressed carbine-gas 12.5 to dump a lot of fouling into the upper.
A suppressed Colt 633 Commando is filthy after 150 rounds of 5.56 (military or civilian).
I would suspect the Criterion (typically with a tighter Wylde chamber for precision, vice a big, fat, .mil 5.56 chamber) is going to have more “Stiction” and be more sensitive to fouling. A carbine-length gas tube is also going to start un-locking while pressurized with case still obturated against the chamber.
Take a look at Criterion’s video at the 2:11 mark and see how much gas is coming back through the chamber on a suppressed rifle (then multiply by five 30-round magazines for 150 rounds. You can see air distortion as high-speed gas bleeds from the vent holes, then the obvious smoke):
You walk a tight balance between precision and functioning while fouled with a suppressed Commando. A few remedies are a chrome-lined GI chamber, mid-length gas, a flow-through suppressor, and piston-operation. An XH heavy buffer and maybe an LMT improved carrier might help with cycle timing but offer nothing for handling pressure.
Your cases are holding a lot of pressure and the primers are letting go as peak system pressure is trying to blow them out of the pockets before the bullet un-corks. I can only assume MEN crimps their primer pockets, otherwise you’d lose a bunch more. Check your bolt face for annular gas leakage around the primer pocket crimp. MEN is typically very good ammo.
I hate to admit it here, but I flat out HATE shooting suppressed ARs. I’m MUCH happier putting on ears and letting my AR breath naturally. With the can everything is dirty. Your brass, your BCG, you air in your face.
Quick shots of the BCG. It’s not clean but that should still be functional right? There was a lot of gas blowback in their promo vid which is interesting. I didn’t notice any the entire time except for the first 2-3 rounds right after I dumped lube on it.
We were estimating that it was moving somewhere around 2800 FPS but didn’t actually chrono it. I don’t know anything about loading but I do know that the MEN doesn’t have crimped primers. Could that be contributing?
Crimped primers will help prevent losing primers in your upper, but the problem remains – your carbine-length gas system with a suppressor is choking itself.
Without gunsmithing I’d first try an XH buffer and an LMT enhanced carrier. You’re going to spend some money.
If you want to keep your present overall system length (with the suppressor you already own) you might try a mid-length gas barrel (port pressure will be lower than with a carbine-length, but overall system pressure time until un-corking is the same). It’ll help, but won’t solve your pressure-time curve issue.
When you clean the bolt keep an eye open for flame cutting around the primer pocket radius on your bolt face:
I LIKE suppressed ARs, and I like the idea and concept behind them. The mechanics are a challenge, as the rifle-carbine were not originally designed for them.
I doubt it’s truly 5.56 pressure ammo. MEN isn’t exactly garbage stuff. I’d guess the combo of the Chamber, Gas system, and Suppressor are just not ideal. The powder burn rate in MEN’s ammo might be a factor too.
I do have EBCGs in both of my 10.5s so I could easily swap a carrier in to try for a bit. I forgot to check the buffer too but I have one of every weight for spares for the A5 so I could easily drop to A5H0. At this point though I’ll probably keep as is and put some more rounds through it then document the issues better. I have an 11.5 Super Duty and a BCM upper that I need to pour rounds through also so it may just be an expensive trip to the range.
Worst case, I’ll give Criterion a shot at fixing it, otherwise maybe I’ll try out the FCD barrel and see how long a SS lasts. At least I trust their CS.
It does look pretty crusty but I have run some filthy guns with soft shooting ammo without issue. Clean rinse and repeat with both MEN and other ammo. I think MEN does a decent job on their ammo, kinda surprised. How violent is the ejection / gun when running? Not that it tells you much but it is a data point, especially if its running hot it should run. Unless that brass just hates that W chamber.
I was taking a private precision course so all single shots really, I tend to notice recoil issues more in a string of fire. That said, the recoil didn’t even register until I took the can off. As soon as I did that, I remember being a bit surprised at how much the felt recoil increased.
I may be able to shoot it this weekend, still going back and forth on whether I should clean it first or not. FWIW, it’s better than how most of my ARs normally look. I rarely clean them and usually it’s a non-issue. The can is still a bit new though and this is my first .233 Wylde chamber, plus the only other time I’ve had popped primers was when I was shooting known shit ammo (Freedom Reman) which all adds to why I was stumped.
Which is what everyone says. It was probably just the positional work we were doing that was less stable that happened to coincide with me pulling the can, but it was definitely noticeable.
I’ve never heard of a dirty rifle running better than a clean and properly lubed one.
I’ve used MEN’s 7.62x51 ammo, but not their 5.56. If stoppages when using any imported ammo were to occur to one of my previously reliable ARs, the ammo is the first thing I’d change…after properly cleaning and lubing it.
