Sig P239 40 S&W Mod

Spurshot · March 2, 2016

Being a former gunsmith, a machinist/toolmaker, and engineer, I have a insatiable appetite for modifying things. In some other posts, I installed a Sig (OEM) Short Reset Trigger group to help the single action trigger function, as well as a full length steel guide rod.

Since I don't do concealed carry with my P239 40 cal, I wanted to do an extended magazine to gain capacity over the standard 7 round single stack. My wife has begun using it for her shooting, since it fits her hands better than the P226 double stack.

I looked at the Sig website for an extended magazine. They do one for the 9mm P239. Nothing for the .40 S&W P239. So, I thought I'd buy a 9mm 10 round extended magazine and see how they did it and if I could use the parts to alter my 40 cal magazines.

It was almost as easy as I thought. The base extension is all FRP (fiberglass reinforced plastic). I disassembled it and found it wouldn't quite fit the 40 mag. The 40 mag was about .040 wider at the base where the extension slides on. I checked a few dimensions with a dial caliper and filed a bit on the FRP base extension and 10-15 mins later I had a 9 round 40 cal mag. 10 rounds won't quite fit. I used the base, the spring and the spring retainer from the 9mm mag and kept the 40 cal follower of course. Seems to be perfectly functional, but I'll test fire it at the range for reliability.

If I don't have any issues, I'll probably modify a couple more. It is a little pricey, since you have to buy 2 mags to make one. I could have simply machined bases from aluminum and made it slightly longer to take the full 10 rounds I wanted, and used some generic Wolff magazine spring material, but this was too easy and it looks factory.

grampadirt · March 3, 2016

Nice work

TJay74 · March 3, 2016

Nice, I am trying to find a (ultra) compact Sig for the wife to try out for her to carry. Needs to be 9mm and light as possible. I already have the P938 and may put her in it, only concern is the flip safety. I would rather have something along the lines of a striker fired system. I bought her a Kahr CM9 but she hates the trigger on it with a passion. She can hit center of the silhouette with it, but she is dead on accurate with the P228 I got or the P938.

Spurshot · March 4, 2016

Nice, I am trying to find a (ultra) compact Sig for the wife to try out for her to carry. Needs to be 9mm and light as possible. I already have the P938 and may put her in it, only concern is the flip safety. I would rather have something along the lines of a striker fired system. I bought her a Kahr CM9 but she hates the trigger on it with a passion. She can hit center of the silhouette with it, but she is dead on accurate with the P228 I got or the P938.

Take her to a store and let her handle a P239 9mm. It's a double action first shot and single action from there. It's not the smallest gun, but it isn't brutal to shoot like really small guns can be in adequate defense calibers. My wife shot 250 rounds of 40 cal out of the pictured gun, in about 4 hours.

TJay74 · March 4, 2016

That is one on my list, along with the S&W MP9c, a XD 9 sub-compact, and a couple other Sig models. I am leaning more towards the models that are around the 21oz range as she doesn't want anything super heavy since she will be carrying it in her purse.