Sounds like a stupid question I know, but I have been having some issues with my BCM 12.5 KINO with PMC Bronze ammo. Let me preface this thread by saying this is NOT a “I think something is wrong with my BCM upper” issue.
First my set-up:
DD SBR Lower (new)
BCM 12.5 KINO Upper (non BFH) unsuppressed (new)
BCM BCG (new)
BCM Mod 4 CH
Spikes ST-T2 buffer/OEM spring
Here is (was?) the issue:
Numerous double feeds. Double feed as in an empty and a live round caught in upper.
My guess is that the malfs were being caused by short stroking likely as a result of weak .223 PMC Bronze ammo and the H2 buffer. The carbine functions 100% with good 5.56 milspec ammo.
The set-up is relatively new. I had only put about 30 rounds down the pipe for initial zero and function tests. All slow fire.
I initially I had numerous double feeds (as defined above) with the PMC ammo when the gun was cold - maybe 2 rounds down the pipe before the double feed. Switched over to 5.56 and was good to go. Shot about 120 rounds of 5.56 doing various rapid fire drills - no issues. Tried the .223 PMC again (another 40 rounds) and it ran just fine.
To the point with my question(s): can a gun function more reliably when warm vs when cold? And, could this be a “break-in” issue - is there such thing with an AR? Anyway, this is a new one to me. I really think that if I had had the H buffer in to begin with I would not have had the issue with the .223 when cold. I do not intend to be satisfied with “it works okay when it’s warm” and I’ll play around with it later in the week, mainly by trying the H buffer.
Ok. Thanks. My bad. I used the definition of “double feed” from an old thread I read about double feeds - this was the definition from Robb Jensen - M4C.net staff.
Anyway, regarding the o-ring, I do not know. It was a new BCM BCG that I ordered with the upper so I ass-u-me no since they usually don’t ship with the o-ring. I will have to verify this.
I would run it for a few hundred more of 5.56 through it, before I would start looking hard at issues. When you have a spent casing still in the chamber, it failed to extract and the new round is unable to feed for obvious reasons. While it might seem its a double feed, your true issue is failure to extract.
If you have a standard H2 or even an H1, I would run that over the spikes from now on, especially if chasing down issues.
When you say a Spikes H2 buffer, are you referring to their ST-T2 buffer? If so, this is not a standard H2 buffer and could be the cause of your problems.
Yes, it is the ST-T2. Somebody gave it to me so I thought I would try it. My 11.5 BCM upper has a standard H2 buffer and eats everything so you might be right.
It’s pretty simple. Remove the extractor and look for the black O-ring around the extractor spring. Sometimes too much extractor tension can cause issues.
An H2 seems a little heavy for PMC bronze which is the lowest power brass cased ammo I have ever come across. I have steel cased ammo with much more punch than it has.
Come on IG gimme some credit… My post may make me seem like I’m clueless regarding all things AR, but I am not that bad… When I cleaned and inspected the BCG when I first got it, I was simply too lazy to remove the extractor to inspect to that detail. I will do that tonight.
Might be a failure to eject. Check the action of the ejector in the bolt. If it’s not moving smoothly it won’t kick the spent case out before trying to load the new one. Could also be the extractor binding as was mentioned earlier.
It was unclear what you meant by double feed. Is the spent case getting pulled out by the bolt?
Is the spent case being left in the chamber, or is it being extracted from the chamber but not ejected? If it’s being extracted but not ejected, this is a symptom of of either short stroking, or a malfunction of the ejector (or both). You need to figure out which problem you have.
Before doing anything, fire your rifle with just a single round loaded in the mag. If the rifle does not lock back on the bolt (make sure it’ locking back on the bolt, not the carrier) then the rifle is short stroking and it’s time to figure out why. If the problem is extraction/ejection, not short stroking, that too will be plain to see
The spent case is being left in the chamber about half way out and the bullet of the feeding round gets wedged between the stuck case and the feed ramp - if that makes sense.
I will run the diagnostics you recommend later this week.
Makes perfect sense. Next question- Is the next case being pushed out of the mag at the rim by the bolt, or is the bolt pushing the next cartridge from the mag somewhere along the body of the case?
The former is an ejection problem. The latter is a sign of short stroking
I was able to get out and troubleshoot this today. Still having issues. Here’s what I tried today:
Per MistWolf’s recommendation, tried one round in mag. Bolt locked back as it was supposed too. This is definitely a Failure to Extract issue. Buffer didn’t matter. I tried the Spikes ST-T2, standard H2 and H buffers. FTE with all. Tried 6-7 different mags (pmags and NHMTG GI), also didn’t matter.
It was only with PMC Bronze ammo. One round fired, the bolt would lock back appropriately but the spent case would be laying loose on top of the mag. The XM193 would extract and eject every time.
I think I may have noticed a small gas leak from the key on the BCG. It is a BCM BCG. It came new with the upper. With today’s round count - about 60 rounds - I have only a total of +/- 175 round through this upper and the BCG. The BCG was well lubed, and when I took it out to inspect below is what I found on one side of the key. With all the lube I had on the BCG it is clear to see what appears to be a leak. Do you think this could be enough to cause this issue?
When I cleaned and inspected the BCG when I first got it, I was simply too lazy to remove the extractor to inspect to that detail. I will do that tonight.