Busmaster stubby lower, bolt latch won't lock the bolt back. Brand new lower, what's the problem, thanks!!

Can you give us a little more info please?

Do you mean you can't manually operate the bolt catch with your thumb/fingers to hold the bolt back, or that the magazine won't activate the bolt catch to hold the bolt back?

Also: Factory lower (for sure) or assembled from parts?

What do you mean by "stubby lower".  Not familiar with that term.

Brand new from factory, Bushmaster lower with stubby stock. Will not lock on empty mag or by using the bolt catch on the side. Switched out lowers using same bolt and  charging handle and it works fine ( a different lower) so I narrowed it down that particular lower. (stubby stock lower) As I said, it's brand new. Looks like I might be sending this off to Bushmaster so they can take a look. Any help until then will be greatly appreciated. Thanks.

Sounds like the bolt catch itself.  Might be out of spec.  not tall enough.  Pop it out and compare it to the one in the other lower.  See if there is a reasonable size difference.  Or for some reason the lower having the mill cut too deep. (highly unlikely from bushmaster)

I had this same problem with my second AR. The problem was that the buttstock screw was too long. It was stopping the bolt/buffer from retracting far enough to activate the bolt catch. Try switching out you buttstock screw for a shorter one. HTH

Thanks... It came with the correct size screw but when I installed a single point sling plate to the front of the stock and a longer screw was needed which in turned was the cause of the problem. I went back to the original screw and it solved the problem. Wish I could buy all of you a beer! [beer] Here's a pic. Testing out the TA31 on this rifle,  but the upper it's going on is at KKF. [img]http://home.nc.rr.com/blueshockey77/acog_stubby.jpg[/img]