I bought this in March this year. The slide fails to lock back after the last round is fired. Have only used decent ammo: CCI Mini Mags, Target & Varmint, CCI Stingers, Federal Punch, & Federal Auto Match. I thought the gun just needed to “break in” a bit, but the problem has remained. The slide also sometimes just releases spontaneously after I have locked it back.

I’m sending it in for a fix, I hope. Otherwise, I like the way the gun works, as long as I take care to load the mags carefully. Sig should make some metal mags for these; I have had some failures to feed occasionally, which I attribute to small flexing of the plastic mags.

Does it lock back when manually operated and you pull the slide back with an empty mag inserted? If so first try shooting one handed left handed - if this results in it locking back on empty, it is your grip not the gun.
The low recoil impulse of a 22 is such the slightest drag from a finger rubbing on the slide could prevent lock back on empty
Locking back on empty on a range rimfire is no big deal, I wouldn’t potentially invite more problems by sending it back for a fix of such an insignificant problem

It’s a common issue with the slide stop itself. It barely engages the slide and is very sensitive. Mine does it constantly.

happened after a few mags when new, sent back has over 1000 now, never a problem
When you clean the insides of the mags, spray them with CRC silicone and when loaded correctly will no longer FTL

The slide failing to lock after the last shot has nothing to do with the magazine. The problem is that the slide lock ends in almost a point where it engages the the lower part of the bolt face.

The solution is to carefully file/sand that point back just a hair. This in effect enlarges and raises the contact area of the bolt stop. Go lightly -- you're just removing a tiny bit of steel.

I have a diagram to illustrate what's to be achieved but I don't know how to attach it to this post.

Thanks for all of your replies. I did send it back for repair and it just came back. I’m taking it to the range tomorrow to see how it works.

Captain127, I did make sure that my fingers were not on the slide during firing, and yes, the slide did sometimes fail to lock even when there was an empty magazine. I’ve learned, to be extra safe, to put my finger on the chamber to make sure there is no round loaded. Once, the slide spontaneously released and bit my finger when I was checking the chamber. That was a big ouch.

I do hope I haven’t invited more problems by sending the gun in, if so, I will just keep sending it back until they get it right. I have since bought a Walther PDP 9mm, which shoots nicely, and a Walther P22Q which shoots well, but is a bit too small. For my range days since my Sig went down for repairs, I’ve been bringing the 9mm & the P22Q. I like shooting .22 because I can shoot a lot more rounds and improve my accuracy with the .22, while still shooting just enough rounds of more expensive 9mm to remain practiced and accurate for center mass, while practicing head shots with the .22. I do like the larger size of the Sig P322 over the Wather P22Q.

Jus228, yes God bless all of our troops, and all vets. I never served and wish I had when I was a young buck. I am though a proud papa of a fast attack submarine sailor who does cybersecurity and other comm tech duties for his boat.