Hesitant AR15

[doorgunner]

Had a dpms that was doing something like this. Long story short, the gas block wast torqued down or have thread locker. After about 200 rounds, the gas block worked loose. I reset it, torqued/thread locker on the Allen screws, problem solved. Now have about 700 rounds since, no problem. So my bet is gas block.

 

[uncle money bags]

Had a dpms that was doing something like this. Long story short, the gas block wast torqued down or have thread locker. After about 200 rounds, the gas block worked loose. I reset it, torqued/thread locker on the Allen screws, problem solved. Now have about 700 rounds since, no problem. So my bet is gas block.

you had a gas block problem that caused the BCG to recoil to its full rearward position and stick there?

 

[aviator41]

I will check the roundness of the upper tonight for sure.

Doorgunner, was the gas block noticeably loose? as in you could move it with your bare hands? My first though was that the gas block might have rotated, but trying to move it by hand is impossible and there is no sign of movement. not sure how this would case a rearward stick.

 

[doorgunner]

Ah, I see whats going on. Gotcha now. I saw that the bolt was hard to move and eject the round. Maybe I should read the whole post first.

 

[jakerz]

I would say take a good look at the buffer/spring, but you already said you have tried it on other lowers. It could be a gas issue. If it's not fully pushing the BCG back to the rear, then the spring will not have enough compression to push the BCG back forward to pick up another round and re-seat.

I guess I didn't read it correctly. I was thinking it was getting caught on the magazine and binding up on the round. Sorry.

 

[aviator41]

well, I had a chance to check this upper this evening, white the machining isn't what I would call stellar, it seems within spec. the wear marks aren't significantly different. So I turned my attention to the BCG and found that the spot right under the gas key where the bolt carrier is machined flat, the sharp edges show exceptional wear, but are still sharp.

This leads me to believe that the bolt carrier is the culprit here. my though is that I very gently and ever so slightly need to round this edge. Before I do, I'd like to get a consensus of what I'm thinking is going on. this spot is very sharp with only the coating being worn down and the steel 'polished' underneath. I'm looking closer at what this may be catching on.
Look just below the gas key, the flat spot on the front, you can just see some wear. hard to photograph, this is down to bare metal.

This is the wear along the charging handle groove, charging handle removed. the machining in the groove is less than idea, but the charging handle covers it so it's not a functional problem I don't think.



This shows roundness of the bolt and the bolt hole.

These photos were taken prior to cleaning, it's just been wiped down to more clearly show where parts are rubbing.

 

[doctorjj]

I thought you had already said that other BCG's did the same thing in this upper? Didn't I read that somewhere? Like second else said, it sounds like you had eliminated possibilities down to where it was this upper as being the only culprit.

If I am wrong about that, then it could be this BCG. Either the sharp part you are talking about or perhaps the cam pin. You might check it.

 

[rickb2202]

And run it juicy. Dont skimp on oil in this area. I use half dextron half 30 wt motor oil mixed. I have seen soldiers carrying this in visine containers and splooging it in the bolt a plenty!

 

[aviator41]

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.

 

[doorgunner]

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.