I finally got a good chance to go shooting, and several times, after I shot the second to last round in a mag, the bolt would lock back, and the last round would just be loose above the magazine. It seems to not always happen, and with any of my mags. In about 250 rounds, it happened about 5 times. Any advice would be appreciated.

That same thing is happening to me on my colt m4. Mine is worse though. It happens every time the magazine is on the last round. Mine is doing it with the factory colt magazine. I talked to the gunsmith at the range and he said to try and shave off some of the plastic on the follower. Don't know if it will work or not. Have not tried it yet. I have a new magazine coming from bushmaster to try. A few shops I have talked to say this is a common problem on the ar15's. Take it for what it's worth. Sorry, not much help.

I have the same problem with an Adventure Line 20 rounder of mine, I've posted about it on the [b]Magazine[/b] forum and the guys [b]there[/b] told me that the feedlips are probably slightly splayed out and may just need bent in a little bit.

Hope I could help

[:)]

It's only a common problem of a bad magazine... the feedlips are bent outward or the lips are just about ready to crack... check the area of the feedlips that are toward the front and compare them to a known good magazine...

Don't shave down your follower, then you have a bad magazine and a bad follower... [;)]

I have also heard this problem attributed to a weak mag spring.  The spring doesn't put enough pressure on the remaining round to hold it tightly against the feedlips, and then the recoil bounces it enough to pop the round out, leaving it on top of the mag.