I just did a trade for an older model Sig 229 that was billed as a 9mm. I knew it had an EFK 9mm threaded barrel and I plan to return it to an OEM barrel. We did the deal in a hurry in a pouring rain so I didn't realize that all the mags were marked 40/357 until I got it home. There are two 10 rd Sig zipper mags and two 12 rd MecGar mags. Now I'm thinking the threaded barrel may be a 9mm conversion. The gun is pristine so I don't really care whether it is 9mm or 40/357 but I need to know which one in order to get the right OEM barrel. There are no markings on the gun or case that otherwise indicate the original caliber. Is there any way to tell other than contacting Sig with the serial number?

Just look at the breech face on the slide and compare it to a 9mm or 40 case rim. Also, older 9mm P229s would not accept a 40/357 magazine.

Sounds like you have a 40/357 that the person converted to 9mm with an aftermarket barrel.

If it is a .40 pistol converted to a 9mm, you are actually in for a treat. The 229 .40 has the lightest recoil of any .40 caliber pistol I have ever shot. They were made for the .40 and Sig did it right on that one.

What size is the front sight?