shot this gun for about 1k rounds, all of a sudden the slide won't lock after last round, but if I manually rack it back, it locks. It does that about 50% of the time

recoil spring?

slide lock spring?

mag follower spring??

thanks

Quoted: mag follower spring??

Ding! Ding! Ding!

We have a winner!

Have you tried different mags yet? Or just the one mag?????????

Yeah you deffinetly need a stonger magazine spring. I had that problem after a few years of heavy use. How old is your gun and magazine by the way? If you have only ran 1K rounds through her, maybe she just needs to be broken in a little bit also. But I would buy more magazines and see if they all have the same problem. I only use factory magazines only for my Beretta 92. If it is still fairly new maybe you could smooth up the follower. Make sure it is being pushed up smoothly.

Check the follower as well, if its plastic/polymer.
I had a Star a few years ago with an identical problem (wouldnt lock on last shot, but would when racked). The lip on the follower that raises the slide lock was worn.

You take the magazine part? If you put it in backwards, it will not lock the slide back reliably.