I went to the range yesterday as it was raining and I knew I would probably be the only one there. I was shooting my P6 with Blazer aluminum ammo and it failed to lock the slide back a couple of times. I did not check to see if it was the same magazine each time. I have fired thousands of rounds of this ammo without any problems.

Is it most likely a magazine problem?

Failure to lock the slide back is generally shooter error, either from riding the slide lock lever or from limp-wristing.

Focus on locking your wrist, try shooting it one-handed, and/or have someone else shoot it.

If that's not it, it could be a weak magazine spring, or a bent/worn follower or slide lock lever.

Thin SIGs, well in some cases SIGs in general, have folks ride the slide lock causing it not to lock back. I do this quite a lot with the P239. Check to make sure that’s not it.

Then check/replace your mag springs.

Blazer aluminum also isn’t exactly premium loaded ammo and it’s not out of the question that maybe a couple rounds had barely enough oooomph to trickle the empty out but not make it to slide lock.

My bet is the first one though.

Most likely the mag spring, or pressure on the slide latch, or combination of the two. I have seen agency guns that took very little pressure on it to keep it from engaging properly.

IMO, it is most likely the ammunition. Different lots can make the difference even though it hasn’t been a problem before.

All the other suggestions are easier to try, but if they don’t work, I recommend trying more powerful ammunition. For example, the Winchester 124 grain NATO load has fixed a couple of slide lock failure problems I’ve seen myself.

Although some guns that will remain nameless to avoid offending their fans are prone to such problems due to not being held firmly enough, when it does occur, it usually manifests itself as ejection failures. It is not a common characteristic of SIGs. If you have extensive experience with the gun, it’s highly unlikely that you suddenly started doing something different for it to be a shooter issue now.

A long running discussion:
https://sigforum.com/eve/forums...50601935/m/749101723

Thanks for the replies. I am fairly certain it is not me as I have been shooting this gun for 15 years or so. Also, I fired my 1911 the same day with no problems. I will pay closer attention next time and isolate the bad magazine. I think I have some Wolfe springs in the drawer.

I think Sigfreund may be on the right track. Try the pistol with some quality 124 grain brass cased ammo. That aluminum cased Blazer 115 grain stuff can be problematic.