Thanks for all the help from the forum members with ideas on how to fix the feed issues with my AR.
To summarize, I didn’t read “the chart” and purchased a M&P lower and a CMMG carbine upper. Had all kinds of issues up front to begin with but after 200 rounds I was down to failure to cycle the next round. You could see that the BCG had dragged on the round enough to put a scratch in it but it either didn’t go back far enough to grab it or some other issue was preventing it from fully cycling.
Once, when I was cleaning it, I took the BCG and removed the bolt, left out the charging handle and slid it into the upper receiver. The BC (with gas key) would reach the gas tube and then rotate slightly when it engaged. I assumed that it was an alignment issue and, with the help of a great local smith, got them aligned. That cut the number of short cycles pretty dramatically but didn’t eliminate them. Next, removed the gas key and you could see some carbon fouling on the BC that lead me to believe that it might be leaking there a bit so re-attached the key and grabbed some R-Guns mags and had one short cycle in 60 rounds.
Not perfect but since I had 1 every 3-5 rounds before its a massive improvement.
I’m using American Eagle 5.56 rounds.
I’m just at 300 rounds so figure I’ll keep going with this till I get to 500 and if it’s gone I’m going to declare victory… If I still have the occasional short cycle I’ll let you know.
Any ideas still greatly appreciated (was thinking of locking the bolt to the rear to soften the buffer spring but that seems like a cop-out. It SHOULD work…)
Thanks again for all the advice and kind thoughts.
Have you checked to see if the gas tube pin is in the FSB.
Have you checked the gas rings .
Quibs has posted very good pictorial on WEVO about function checking http://www.weaponevolution.com/forum/showthread.php?p=18735#post18735
He has a few other pictorial’s on WEVO you might want to check them out also.
Some guys also recommend lapping the gas key just to make sure it is flat and that you are getting a good seal. Might be worth trying also.
Never tried R-gun mags but it might be worth your wild to try some P-mags they have the best record for reliability. One other thing you said when you got the gas tube re aligned it dramatically helped but you are still having short strokes are you sure you are identifying the malfunction correctly? We are all human and I have made the same mistake before miss- identified the malfunction.
And with all trouble shooting try the simple things first one at a time and work your way up the process of elimination is your friend just keep plugging away at it and good luck and keep us updated on whats going on.
Appreciate the feedback. I’ll try the P-mags (since they cost about half of what I paid as well…)
Would you describe the pinning issue on the FSB for me in a bit more detail? I’m not exactly sure what I should be looking for.
Thanks!
Its a roll pin that is in the FSB it holds the gas tube in. 99% of the time it is in there but it some time it does gets left out and you will have gas escaping.
Its a teeny tiny little roll pin on the front sight very close to the gas tube.
Ok this pic sucks but look at the front sight and you will see a roll pin that attaches the gas tube to the front sight bus.The description is the gas tube roll pin.
Found it!
Yes it’s in place.
How complex is it to remove the gas block and check the hole and alignment? I’m pretty good mechanically but it would be a first for me.
And thanks a bunch for the ideas.
Seems that I remember is that on cmmg upper the tapered pins are installed backwards so expect to use some force to remove them also I would have new pins to replace the old ones and try to install the new pins the correct way.
Got it… looks relatively straightforward.
I’m just running out of other options at this point so maybe that’s next…
Sigh…
Maybe going with a lighter buffer spring would be simpler…
Funny how, in thousands of rounds in the military I’ve never had these problems.
Again, thanks.
you may want to see if CMMG will take care of your upper for you… just an idea.
bummer that you’re having trouble. don’t give up though, AR’s are very reliable weapons, you just got a defective piece in there somewhere.
On the lower tier barrels the gas ports normally run on the large side.
Using a reduced buffer spring may get it running but it will be masking the real problem on the plus side you get it running correctly the knowledge gained will stay with you a life time;) But in the same breath I will say if you want to see if cmmg can correct the problem for you and are not interested in having to fix it your self either way is fine
All great points.
I think I’ll start with CMMG since I’d hate to do something stupid and expensive… but at some point I need to learn how to do this myself.
If nothing else my break in procedure is producing a bunch of empty brass to reload!
you might want to check them out also.
but it might be worth your wild to try some P-mags they have the best record for reliability. One other thing you said when you got the gas tube re aligned it dramatically helped but you are still having short strokes are you sure you are identifying the malfunction correctly? We are all human and I have made the same mistake before miss- identified the malfunction.
just keep plugging away at it and good luck and keep us updated on whats going on.