My nephew bought his first handgun an anib used M&P Compact from a "friend" without realizing the cost of .357 Sig ammo. My thought is to recommend he get a second barrel in .40 to keep his shooting costs down.

Some questions........(I'm a 3rd generation guy, and don't own any striker fired guns )

Can you change a S&W M&P compact from .357 Sig to .40 S&W?
Do you need to change the recoil spring?
Would the new barrel need to be fitted or would it be a simple drop-in?

Thanks
BAM

My understanding is that they can be dropped in. Since the 357 is from the .40 case to begin with, you can use the 357 mags for 40.

Others may know more about this, but this is what i have heard

It was my understanding that at one time the .40 could be converted to .357, and also to a 9mm with drop in barrels, but not the other way around. But I see now that the .40 replacement barrel also fits as a conversion barrel for a .357 pistol.
If you really want to save some money get the 9mm conversion barrel. It is advertised to fit the .357 also. You will have to get the 9mm mags for it.

The 40 should be a straight drop-in, same mags and springs. There are some aftermarket barrels that are suppose to allow 9mm to be fired from .40 guns, but your counting on the extractor and the larger breechface to work with the smaller 9mm case. Might be fine to play with on the range but I wouldn't bet my life on it.

This, I got in on the 357 M&P deal on Gunbroker. A 40S&W barrel is all I need to convert it to fire .40. The recoil springs and mags are the same. The mags are even marked 357/40.

The 357 M&P is a sweet gun in it's own right.

Speaking of that Storm Lake 9mm conversion barrel, I now have 250 flawless rounds through my former 40c and am thoroughly impressed. It has helped persuade a couple friends to look at the M&P, and I'm even thinking about a full size. I still like the .40 for carry, but the 9mm is a great shooter.

On the barrel swap issue, it's actually easier to get ahold of a .40 barrel than the .357, of which the only supplier I've found is S&W. If I could only swap it to .45 I'd have a full set in one gun.

__________________
Fast is fine;accurate is final

Thanks for the feedback ; I will pass the information on.

BAM