it's probably one of two things, either the mags or the slide catch. If te mag springs are two weak, the slide won't hold back after the last round. I had the same problem with my 239. Call sig and let them know about it. In my case they sent me two new mags and that was that. The problem contuined after a roll pin broke and sig changed the roll pin and he mag catch and I haven't had the problem since.
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