P239: Converting 7rd mag to 8rd mag

[wacky_doug]

Hi MA legal experts:

I have a Sig P239 in 40 and 357. The 40 mags are 7rd flush fit. The 357 mags are 8rd extended. While the mag bodies are not interchangeable (you can't put a 40 round in a 357 mag), the mag bases are.

Is it legal to swap mag bases?

 

[appraiser]

IMHO and I have been wrong before, since you are not creating a high capacity magazine you should be fine.

My question is since the 40S&W and .357sig rounds are very similar, and most manufacturers use the same magazine design for both guns, they just mark them differently, does Sig make 2 different 239 guns to prevent the magazines from being interchangeable?

I know in my .40's I can swap out the barrels and use the same mags to shoot either .357Sig or .40S&W

 

[drgrant]

The mags both hold less than 10 rounds so you can legally do whatever the heck you want with them. It's that simple.

-Mike

 

[wacky_doug]

Depends on the gun.

The P226 and P229 use the same mag for 40 and 357. They are double stack mags. So for these guns, it's only a barrel swap.

The P239 uses a single stack mag, and the mag bodies are definitely different for each caliber. A 40 round won't even fit in the 357 mag. You have to swap both the barrel and use the right mag to change calibers.

I was surprised to see that the springs are identical between the 7rd 40 and the 8rd 357 mags. Only the mag base and spring base are different.

 

[drgrant]

My question is since the 40S&W and .357sig rounds are very similar, and most manufacturers use the same magazine design for both guns, they just mark them differently, does Sig make 2 different 239 guns to prevent the magazines from being interchangeable?

IIRC the .40/.357 P239 frames are the same. They made the mags different to improve feed reliability more than likely. I'd bet the .40 mags will work (to some degree) with .357. Not sure how reliable that is, though.

-Mike