AR lock-back on empty mag

[Sespe]

My new-to-me AR won't lock back on an empty mag 100% of the time. It's only about 20%. I've tried a no-name metal 10 rounder and 2 PMAGs. What should I check first?

[69Mach1]

Did you put it together? If you did, was the proper bolt release spring used?

[Noobert]

can you 100% manually lock it back? do the followers of your mags push against the bolt catch?

[Sespe]

I did not assemble the lower, not sure if it was factory or not.

Yes, I can manually lock it back 100% It does take strong effort on the bottom of the catch. The mag followers do push on the catch.

Now, it's been over 15 years since I used a true M16A2, but I seem to remember them being more positive than this.

I can get pictures in the morning if that would help...

[Sespe]

Took a picture this morning:



It feels quite gritty when moving back and forth. Should I just pop the catch out and clean it?

The rifle has only 60 rounds through it so far.

[Noobert]

is the bolt catch lubed?

[jamesob]

it looks like the hammer might have been dropped on the receiver. if that happened it could make the bolt catch a little tight. take a air blower, lube and blow it out real good.

[MKfan]

My Doublestar lower had the same problem, when I would manually lock the bolt back the catch also felt gritty. I pulled the catch out, filed it a little thinner, and reinstalled it, it works fine now.

[Josh3239]

The chance it is your follower or anything in your lower is low. Most failures for the bolt to lock back is a gas problem. Lets hear the barrel specs and what extention spring and buffer you are using.

[Sespe]

The upper was built by Compass Lake Engineering in Florida.
Upper is A2 receiver,
Krieger Stainless Steel 1-7" twist barrel Free floating handguard,
Lower is Doublestar with Rock River Arms 2 stage match trigger.

(from the ad)

I was playing around with the windage-adjustable front sight, this seems like a good way to mess up the gas block.

[Josh3239]

Barrel length and gas system? The location of the gas port is what is most important; carbine, midlength, or rifle length? Windage adjustable front sights, do they make those or do you mean the elevation? I assume you are using the standard pyramid/triangle style front sight base/gas block? If so, it is unlikely that is out of alignment. Also, do you know what buffer is in your rifle? If not, separate your upper and lower and look at the flat side of your buffer, is there anything engraved on it?