Hesitant AR15

[uncle money bags]

Yes I absolutely did, I have had two other bcg's in this upper do the same thing. My original thought was close tolerances in this upper receiver, making all bcg's hang in this upper. This is the original BCG I bought for this receiver, so it's the one that has had the most time and rounds through it for this rifle. the other carriers have been put back in their perspective rifles and kept that way.

Putting other bcg's in this upper was a trouble shooting point. since I can't see obvious wear points on the receiver, but I can on the bcg, it seems to be a natural place to 'tweak' - but I'm looking forward opinions.

the wear I see on the BCG is not abnormal.
did you try the suspect BCG in a known good upper?
Probably unnecessary, as I am 95% sure the upper receiver is the problem.
I always leave 5% to blame on unicorn farts.

 

[aviator41]

I was thinking of using valve lapping compound with cloth wheel moving at slow speed in a pin vise. all by hand, no dremel or grinder.

 

[uncle money bags]

I was thinking of using valve lapping compound with cloth wheel moving at slow speed in a pin vise. all by hand, no dremel or grinder.

Using it on what?

 

[uncle money bags]

I would be hesitant to grind on the BCG, but that's just me. If I were going to go that route, I would get some grinding compound, rub it around the suspected area, and with the mag removed, use the charging handle and repeatedly cycle the bolt.

If anything, this is the way to do it if you are dead set on not replacing the receiver. at least this way it will be the soft aluminum being finished away at a much higher rate than the steel of the BCG.

 

[aviator41]

will try the bcg in another rifle this week. my only concern with using grinding compound is that it would wear away the finish on the bolt, is this something I shouldn't be concerned about?

 

[Hump66]

If you get it functioning properly, you will wear the finish off the BCG on your own.

 

[uncle money bags]

If multiple bcg failed to work properly in this upper; all of them having the same type of problem, then the upper is the issue.
You have eliminated the other variables that would cause this malfunction. It may seem like the easy solution is to start messing with the bcg and modifying it to work with that upper, and i can understand the desire to get your gun up and running. However, several members have given good advice regarding your issue, and i am willing to bet one of them would be happy to look over the gun and help you, including me.

I know that changing or fixing the upper may seem like a hassle, but according to the evidence you have provided it is the correct hassle. If you start down the rabbit hole chasing a solution by changing the dimensions of good parts to fit bad parts you stand a good chance of making this worse. Anyway, i wish you luck. Keep us posted, im sure this will be a learning experience for several people.

 

[ASP785]

I know that changing or fixing the upper may seem like a hassle, but according to the evidence you have provided it is the correct hassle. If you start down the rabbit hole chasing a solution by changing the dimensions of good parts to fit bad parts you stand a good chance of making this worse. Anyway, i wish you luck. Keep us posted, im sure this will be a learning experience for several people.

Heed this advice and fix it once, fix it right.

 

[kdh77]

From what I have read so far, it sounds like you may have a mis-alignment between the upper and lower receiver causing the bcg to bind in the buffer tube. Also the bolt may be traveling too far to the rear and jamming up. A quick remedy for that is to drop a quarter or two in the bottom of the buffer tube. Just make sure that the bolt will travel far enough to cycle.

 

[mr ed]

measure id of takedown pin holes are they round or oblong?
is the fit between upper and lower really tight or loose and wobbly?

Some uppers need fitting and instead of removing metal from the bottom of the upper to make them sit lower
people just wallow out the pin holes. and have this problem from the upper sitting too high and causing the bcg to bind.
it only takes a slight bind to jam up the gun, but not enough to really show wear with only 600 rounds thru it.