what did I do???

[tufenuf]

I just finished my black badge course using my Glock 22 last weekend.
The gun shot great no problems at all. I shot 600 or so rounds from the course and shooting on my own.

So I clean the gun and the mags. Well after using it today the slide will not lock open everytime on the last shot. Works sometimes and not others. What did I screw up. I have pulled it apart and cleaned it before without this happening. I think that it may be the mags but I am not sure.

Any help is good thanks

 

[Stevo]

Did you re-install all of the mag followers correctly? I'm not familiar with Glock mags, but can you put the follower in backwards?