Bolt carrier locking back on loaded mag.

[jetinteriorguy]

I had a weird experience today. I was working up a load in my PSA AR10 in 6.5 CM and the BCG kept locking back even though there was still cartridges in the magazine. I’m not an AR expert but have logged well over 5000 rounds in various AR’s over the years and in this particular rifle at least 500 rounds and have never had this happen. This is a Gen II rifle with a Geiselle two stage trigger. What in the world would cause this to happen? It did this from the starting load all the way up to the max load.

 

[rickyrick]

Does it do it with all magazines?
That’s where I’d start.

 

[Nanuk]

Are you hitting the bolt catch? It the bolt catch broken? The spring?

 

[stagpanther]

Creedmoor is a tricky bird in an AR--does it happen no matter what magazine you use? My first guess would be a pitching/tilt of the magazine follower. I usually trim back the feed lips on all my magazines that I use with the creedmoors. Related to this--are you sure the bolt is locking all the way back--or catching on a cartridge?

 

[jetinteriorguy]

I figured it out. The spring is either missing or broken on the bolt release and it’s just flopping loose. I’m going to remove it today and fix it. I know it can’t just fall out and being broken seems pretty unlikely, but if it was just plain missing from the start seems pretty weird that it took this long to malfunction.

 

[jetinteriorguy]

I removed the bolt catch, and the spring and little plunger are still in there but they are jammed in too far. The spring still has some action to it but it only protrudes so far then it sticks. I sprayed some penetrating oil in to see if it will shake loose but nothing happening so far. I’m sure open to ideas on getting this out.

 

[jetinteriorguy]

I got it figured out and all is good. I just kept inserting drill bits from my numbered drill bit kit until I found one that fit tightly in the hole. Then I put it in a pin vise and inserted it and gave it a few twists by hand and everything popped loose. I then went the next size up and ran it all the way in by hand to ever so slightly enlarge the hole. After this I went up a few more sizes and lightly chamfered the end of the hole. Cleaned everything out, put in a small drop of oil using a micro oiler and assembled it. Now everything works fine again. I’m guessing somehow the opening of the hole got slightly peened from the recoil acting on the bolt release so the plunger was stuck. I also chucked the plunger in my drill and turned the rounded end on a hone to smooth off any edge that might get caught in the future.

 

[jetinteriorguy]

Creedmoor is a tricky bird in an AR--does it happen no matter what magazine you use? My first guess would be a pitching/tilt of the magazine follower. I usually trim back the feed lips on all my magazines that I use with the creedmoors. Related to this--are you sure the bolt is locking all the way back--or catching on a cartridge?

I’ve had really good reliability with this rifle, no misfeeds or ejection issues once I got the gas block adjusted. This rifle is just a good reliable shooter, even working up loads it seldom shoots over 2 MOA whether the barrel is hot or cold no matter what the powder charge is, and within accuracy nodes 3/4 MOA or better is the norm. The barrel runs nice and clean and everything about this rifle is just a good solid dependable performer so far. When I first got it the brass had marks like rings/scratches around the cases. I looked at the chamber and there were clear machine marks. PSA sent me a return label and I sent it back. Less than a week later I got it back, checked out the chamber and could still lightly see the machine marks. I shot it and accuracy was perfectly fine and no more marks on the brass so I’m a happy camper. I was a bit disappointed they didn’t replace the barrel instead of just polishing the chamber but what they did worked fine and the service was excellent and I have a lovely rifle so all is good in the end.

 

[stagpanther]

Sounds a bit like your detent pin in the bolt catch was either backwards or the wrong one--was it jammed down inside the spring? I probably would have replaced the bolt catch assembly before performing "invasive surgery" on the lower. I'm a bit mystified how the bolt catch would lock back the bolt if it was loose and not working. Anyways, you fixed it and that's what counts.

PS--it' also possible to "lock" the bolt catch into place if you pinch the roll pin at an angle when driving it into the receiver to hold the catch in place.

 

[4V50 Gary]

Glad you diagnosed and corrected it.

 

[jetinteriorguy]

Sounds a bit like your detent pin in the bolt catch was either backwards or the wrong one--was it jammed down inside the spring? I probably would have replaced the bolt catch assembly before performing "invasive surgery" on the lower. I'm a bit mystified how the bolt catch would lock back the bolt if it was loose and not working. Anyways, you fixed it and that's what counts.

PS--it' also possible to "lock" the bolt catch into place if you pinch the roll pin at an angle when driving it into the receiver to hold the catch in place.

The parts were correct, I purchased this as a complete rifle from PSA. The surgery was very minor, the bit I used to ‘enlarge’ the hole was only .002” larger in diameter than the bit that fit perfect in the hole so very little material if any was remove, it mostly just removed the finish exposing the raw aluminum. My guess is the recoil caused it to flop up into the lock position, I noticed sometimes it didn’t even look like the release handle was sticking out but when the trigger was dead I’d push the release and it would move just enough to drop the BCG. It didn’t lock on every round, probably once or twice on each five round group. As always, I appreciate everyone’s thoughts on this problem.