Previous 2 trips to the range, every once in a while the 9mm compact's slide decided to go ahead and lock itself back midway through a magazine. I can rack it and keep shooting.

After the first time this happened, I numbered the 3 magazines to see if one might be causing the problems. Last night I shot over 200 rounds and it does not seem to be any one magazine in particular (or maybe all of them).

Any ideas on what's going on?

That was my first thought.

Make sure the spring (and washer in some cases) that works the slide lock is clear of debris. When you get the slide off you will see what I am talking about. Also, make sure the area were the lever meets the frame/grip is clean too. Something is making it stick up. This is leaning more to the user. It could be your thumb touching it just enough (during recoil/cycle) to make it catch the slide. That is the most common issue in this case, shooter not the gun.

I think the washer on the spring was an after thought by Sig due to the problems with slide lock. In my case the slide would slam shut when I inserted a full mag. I sent it back and they fixed the problem, but I'm not sure if the washer was there before I sent it back. It works fine now. Well, I say that. I just got the slide and controls back from CCR for Cer-Plate. I can't wait to see how it performs. The slide does seem a little tighter due to the plating. You can check out my P250C .45 here. The latest is at the bottom of the page.

http://www.p250sig.com/f...-do-you-think.aspx#2053

I had this problem on my last trip to the range . My P250C would'nt lock back after emptying the mag. It happened with both of my mags, one came with the gun, the second I bought after but it is exactly the same. The gunsmith at the range ( true old fashioned gunsmith) looked at it and told me the mag is not pushing on the slide catch once its empty. he showed me that there's a little 'play' when the mag is cipped in and that with out it this wouldn't happen.
I actually went out to the range after talking to him, applied pressure to the mag and the slide locked back like supposed to.

Don't know what to do... is this a mag issue? gun issue? This was only my second time shooting this gun, on my first I shot around 100 rounds from new and never had this problem.