So I am thinking about grabbing a Sig p239 as a CCW weapon. Was checking out different gun sights today and noticed that barrels are pretty cheap to buy. Thinking about getting the 239 in .40 and then buying a .357 barrel....in case i feel like switching it up a bit. So my question: this will not interfere with reliability in any way will it? Is a .357 barrel designed to fit into a .40 frame? I am pretty sure they are interchangable but this moron i know got me all concerned. And i want to carry this, so I dont want problems. Thank you guys for pitying a Sig noob..........

Factory 357 barrel will work fine. You may also need 357 mags. I know you can't use 40 ammo in 357 mags but you should be able to use 357 ammo in 40 mags.

The 239 in .357 uses a .357 magazine.  I don't know why.  My 226 mags are marked .357/.40, but the 239 mags have a step towards the front that the .40 won't go into.  Having said that the switch from .357 to .40 would only mean a barrel and magazines, still pretty easy.

My 239 is a very slick setup.  Dead nuts reliable.  And it barks.

The 357 barrel should work fine. But fire a few hundred rounds of your carry ammo to be sure. I do this with Any gun I carry or plan to use for SD.

Quoted: Factory 357 barrel will work fine. You may also need 357 mags. I know you can't use 40 ammo in 357 mags but you should be able to use 357 ammo in 40 mags.

Really?  The 239 must be different than the 226 and 229 in that respect then, the mags for those are identical and have both calibers marked on the side of them.  I learn something new every day, it's just a matter of how much of that learning I commit to long term memory.

What about (in the p239) going from 9mm to .40?  Or .40 to 9mm?  Does this result in the same reliability?  

-Phil

Quoted: What about (in the p239) going from 9mm to .40?  Or .40 to 9mm?  Does this result in the same reliability?   -Phil

Don't listen to this kid, I know him. If you give him attention he will stalk you forever.

Just kidding man, hope you are having a fun day in scenic Baghdad!