Seems to go in my .40 and test functions just fine. Goes in to battery no problem.

My mags are marked .40. Will they work with .357 sig ammo or do I need mags specific to .357 sig?

Thanks guys and gals.

Mags are the same. Many are marked with both calibers.

357 SIG ammunition usually works fine in 40 S&W P239 magazines. The difference between the mags is that the 357-specific version have internal ribs that contact the shoulder of the 357 cases and keep them from moving forward. That doesn’t seem to be very important, though, because many users have used 357 in 40 magazines with no problem.

What doesn’t work at all is to load 40 ammunition in 357 mags; the ribs I mentioned prevent that.

Added: I have never seen P239 magazines marked with both cartridge designations. That’s a thing with P226 and P229 mags, but unless SIG started doing that later than when I acquired my pistol and magazines, that may be a mistaken claim.
(I would be curious to see any such marked that way.)

^ My dad's '96 P239 mags (3 or 4) are all marked 40S&W only.

I have some that are marked 357 and some that are marked 40, but none that say both.

quote:

Originally posted by Nontypical:
I have some that are marked 357 and some that are marked 40, but none that say both.

Same here, 100%.

Great guys, thank you.

Same her as Sigfreund stated, no mags for mine double stamped.

I have had some folks mention trouble firing 357 with 40 mags, if
working a course on the range or working movement courses in training.

It seems sometimes the 357 rounds would move forward as stated above.
On some barrels, the ramp may have been longer preventing the round to feed.

Just a tiny thought.

You can get new 357 sig mags at mgw for $26 each, just fyi.