Any difference between .40 & 9mm besides the barrel?

[Lost Lake]

I have looked at diagrams and parts lists and read about so many people dropping 9mm barrels into .40 M&P's but there are always those out there that contend this is dangerous.

A call to S&W got a tech that said officially he must say a person should buy a new gun to shoot 9mm (wink wink.... He actually said "wink wink"), so the impression I got is that the weapons are identical except for the barrel and the caliber engraving on the slide.

If someone has a .40 and a 9mm or .357 could you see if the gun itself is identical? With all the successful swaps out there and considering the costs of producing 3 different guns with three times the parts, I'm betting the barrels are the only difference.

 

[crispy]

and the mags...

 

[handgunner356]

The 40/357 uses a heavier slide than the 9mm, also the breech would be larger for the 40/357 rim. By using the heavier slide it allows them to use the same recoil spring in both 9 and 40 guns. The only downside to droping in the 9mm barrel is you're counting on the extractor to make up the difference in the breechface size. With lower powered 9mm ammo you might also need a lighter recoil spring because of the heavier slide, probably fine for the range but I'd never bet my life on that setup.

 

[S&W Rover]

The frame rails on the front locking block are larger on the M&P40 than the M&P9 (the rails on the sear housing block, in the rear of the gun, are the same on both models).

A .40 round shouldn't fit the 9mm breech face, so while it is possible to put a M&P40 barrel into a M&P9 slide, it shouldn't be functional. However, it is possible to put a 40 barrel and a 40 slide on a 9mm frame, and that is not advisable, given the smaller size of the frame rails in the front of the 9's frame.

The slide stop is located a few mm's more forward on the frame of the M&P9 than on the M&P40 -- although this doesn't seem to make any practical difference (the slide stop notch is in the same location on both the 40 and the 9 slides).

 

[OKFC05]

I'm betting the barrels are the only difference.

You lose. There is about .020" difference in the breechface, and that makes the 9mm cartridge a loose fit in the .40 breechface. A conversion 9mm barrel generally works in a .40 gun, and sometimes the magazines also work well enough to get by.
Personally, I wouldn't trust my life to a conversion setup for carry, but several people use them at the range for practice.

The .357 and .40 are identical except for the barrel: it is essentially the same cartridge necked down.

 

[SMMAssociates]

Just between us girls, the 40C slide (& such) fits and works fine on top of a 9C frame, and vice versa....

I don't see any difference.... I've not mic'd anything, though.

But the .40 breech face is larger, so while a barrel swap from .40 to 9mm seems to be easy enough, you can't go the other way. I'm told (no experience with it) that the Storm Lake barrel, rather than an S&W "parts" barrel is a better choice.

(IMHO, you have to use the appropriate magazines, but they'll fit either way.)

Regards,

 

[missiondude]

The frame rails on the front locking block are larger on the M&P40 than the M&P9 (the rails on the sear housing block, in the rear of the gun, are the same on both models).

A .40 round shouldn't fit the 9mm breech face, so while it is possible to put a M&P40 barrel into a M&P9 slide, it shouldn't be functional. However, it is possible to put a 40 barrel and a 40 slide on a 9mm frame, and that is not advisable, given the smaller size of the frame rails in the front of the 9's frame.

The slide stop is located a few mm's more forward on the frame of the M&P9 than on the M&P40 -- although this doesn't seem to make any practical difference (the slide stop notch is in the same location on both the 40 and the 9 slides).

Last time I looked, the part #'s for the locking blocks on the 40 and 9 were the same. Are you 100% sure they are different parts???

 

[S&W Rover]

Mine at least are different.

On the left, M&P40 Ser MRF8XXX; on the right, M&P9 Ser DUB8XXX.

The rails on the M&P40, integral to the locking block, appear larger. Another difference, harder to see here: the slide stop lever on the M&P9 is a mm or two further aft of the same part on the M&P40.

Would seem to indicate it is not a good idea to put a .40 slide/barrel on a 9 frame, although it will fit and seem to function.

On the other hand, the difference between my two full-size frames and locking blocks may be vintage, rather than model, I don't know for sure.