Turbo, The magazine does activate the slide stop on the last round, but in my case, I believe the barrel movement caused this to not happen for whatever reason. I have never had a problem with my .40 barrel or magazine. It could of been the slight amount of play might of been enough to not engage the slide stop. First I thought it was my finger doing it while I was shooting, so I made a conscious effort to keep my finger away from the slide release. When I put the .40 barrel back in, not a single problem.