New AR Build - BCG Getting Stuck in Rear Position

[MachIVshooter]

Something is obviously causing the carrier or buffer to bind in the rearward position. Having cycled it a few times, you should be able to see witness marks that are a tell. I've see receiver extensions that were too shallow, small on the ID, and which had the threads cut crooked. Tube isn't the only possibility, but the most likely.

"You're not really supposed to "lube" the buffer and spring. Clean with CLP, then wipe dry." -- dogmush

Nonsense. Lubing makes for better and quieter operation.

Yup. Never found it necessary with carbine parts, but I grease the spring on rifle length systems.

 

[allivak]

What? If something is out of spec, figuring out what that is and fixing/replacing it is the only way to fix the problem. Seems like it might possibly be helpful to identify it.

yes precisely my point...identifying WHAT part(s) is causing the problem is more important(and productive) than identifying WHO made the part(s). no brand on the market is without its share of problems...

 

[tarosean]

Pull the gun apart, pull the BCG, and inspect it all closely. Take photos and post if your unsure of something.

In the charging position the BCG goes from the Upper through the Lower and into the tube.. So you need to concentrate on those 4 things.

Look for wear indicators as MachIV indicated.

 

[allivak]

yes I understand where the BCG operates....but because it keeps getting hung up, it was very difficult and time consuming to "dry cycle" the BCG enough times to start seeing wear but I finally think I've got some results....here are some pictures.

first of all, I have a strong hunch that it is NOT the detent or buffer tube assembly....but is it OK to assemble the AR without the detent in place to try and narrow down the possibilities? I actually think it may be catching on the hammer?!?!?

if you look closely at the pictures(its a little difficult to see), you can clearly see TWO distinct and separate wear marks on the bottom side of the BCG....one of them(the smaller one) looks like its from the detent and it does not appear to be too abnormal nor responsible for the BCG hanging up. however, the second wear mark(the longer, wider one that is highly visible), appears to be much too wide to be caused by the detent and is clearly causing significant friction. the only other thing that could really be in the way is the hammer....

one other thing I have noticed is that my upper/lower receivers do not have the best fit...there is quite a bit of play and even a significant gap between the two receivers(although from everything I've been told, this is completely normal, if not slightly beneficial and to be expected). reason I mention this is because its quite strange...as soon as I put in the BCG and CH into the upper and close her back up, all the slack/wobble goes away and the gun suddenly has a very tight fit....clearly something is out of spec/alignment here.

any ideas how to fix this? Most importantly, is the gun safe to fire and handle with this sort of behavior? I am worried about the BCG getting stuck back and then randomly slamming home without warning and causing an AD....i'm pretty sure it won't discharge, but I rather be safe than sorry.

thanks again guys

 

[tarosean]

The wear is extremely uneven. Does your bolt catch show the same type wear on one side?

The hammer should touch the BCG however it will leave a racing stripe down the middle.