I recently bought a slightly used P239 with both 40, and 357 barrels...I also purchased a couple used 357 magazines from another source...The 357 magazines will not hold the slide back after the last shot in either of the two p239s that I own...all the 40 Cal magazines that I have do hold the slide back in both pistols... What do I need to do to get them to function properly..?:

Are the recently acquired magazines OEM SIG Sauer or aftermarket? Have you disassembled, cleaned, and carefully inspected them? Any obvious differences in the followers?

Yes, they are original SIg mags....look to be nearly new...I took the slide off and observed the follower, the 357 followers might be slightly shorter, they contact the lock back lever.....I will disassemble them and clean.

If those magazines will lock the slide back when the gun is empty, then something else is going on. Are you shooting factory ammunition or reloads? Have you tried different brands of ammunition?

They wont reliably lock it back when empty

Let me rephrase my question. Will those magazines lock the slide back when you manually pull the slide to the rear on an empty gun, i.e. not firing?

Yes...they won't lock the slide back reliably when hand cycling...I think the magazine springs might be weak, or binding slightly..?

I bought a used p239 in 40 that looked brand new. When I function tested it it would not reliably lock back the slide with an empty magazine. I cleaned the mags and found that the followers were tight in the mag body, and were binding up at the top of the magazine which then did not lock the slide back. I relieved the edges of the followers and kept trying till the followers no longer bound up. I did not have to take much off the followers for them to function correctly, might be your problem also.

^^^^^ This is worth a look. I doubt that the springs are weak.

You can also check things with the slide off, as you did.

Do it again though and consider that the slide lock spring is applying pressure to keep the lever down. The magazine spring is pushing the follower up and it has to push upward on the slide lock lever with enough force to overcome the slide lock lever spring. That amount of force should be significant to solidly lift the slide lock.

There could be a problem with the way the mags fit, with the mag spring, or with the magazine follower having too much friction or not having a high enough area to contact and push up properly on the slide lock lever tab.

All of this is readily discernable with the slide of and fiddling with it and an empty mag.

A week or so ago, I disassembled both 357 magazines, cleaned the insides...I noticed the followers we both a little rough on the sides...I took a rubber polishing point on a Dremel...NOT a grinding point, and polished all the edges of the followers...Today I loaded up both magazines and shot them...The slide locks back on the last shot every time..!...Thanks to everyone for the help in solving my problem..!

This message has been edited. Last edited by: acpick,

I have two P 220s and the one locks back readily with all of my mags. Some are the ACT and some old 7 round sigs. So I have tried this follower tweaking trick and will see how it goes. Is likely the slide lock lever on the P220ST but want to eliminate other likely causes first. I have read all the pages on the sticky post about slides not locking back. I hate intermittent problems. Will try Sig mags found a place that doesn’t want an arm and a leg. wish me luck