HK USP Compact slide compatibility 40 vs 9mm

[HCM]

Question:

Will a USP Compact 9mm slide drop in & function if installed on an HK USP Compact .40 cal lower / frame ?

Could it work if you swapped ejectors ?

[fatdog]

All parts in the lower of the usp/c are identical between 9/40/357 including ejector and every part of the action group. The slides will work no matter what the lower started out as. Only the USP/c 45 is a different frame.

9/40/357 conversions in USP/c only require the magazine and a complete upper for the cartridge in question.

[JRB]

All parts in the lower of the usp/c are identical between 9/40/357 including ejector and every part of the action group. The slides will work no matter what the lower started out as. Only the USP/c 45 is a different frame.

9/40/357 conversions in USP/c only require the magazine and a complete upper for the cartridge in question.

.40 S&W to .357 Sig (and vice versa) only requires a barrel swap.

[HCM]

All parts in the lower of the usp/c are identical between 9/40/357 including ejector and every part of the action group. The slides will work no matter what the lower started out as. Only the USP/c 45 is a different frame.

9/40/357 conversions in USP/c only require the magazine and a complete upper for the cartridge in question.

Thank you!

[RealSelf]

All parts in the lower of the usp/c are identical between 9/40/357 including ejector and every part of the action group. The slides will work no matter what the lower started out as. Only the USP/c 45 is a different frame.

9/40/357 conversions in USP/c only require the magazine and a complete upper for the cartridge in question.

So this is true also of the Full Size USP, one can simply swap complete upper's and magazines between frames going from 9 to .40?

[fatdog]

So this is true also of the Full Size USP, one can simply swap complete upper's and magazines between frames going from 9 to .40?

I have not personally done that but my understanding is the frames are the same. The action parts themselves on compact and full size are the same. That is why there is one LEM kit that fits all of them.

[Sig_Fiend]

So this is true also of the Full Size USP, one can simply swap complete upper's and magazines between frames going from 9 to .40?

Correct. There's only one edge case I know of. Early slides prior to ~'97-98 have a smaller relief cut for the disconnector. This is at least the case for the old .40s&w slides, but I'm not 100% sure about the 9mm ones.

If buying a used slide of Ebay, Gunbroker, or wherever I've seen a significant number of them that appear to be these older slides. If using one of the old slides on a newer frame, the trigger will be dead.

To fix this, simply swap out the disconnector to the old style which should be part #214160. Finding one is difficult. I eventually found one on Ebay. You can tell the difference by the shorter flat section on the top of it in comparison to the newer style which has a longer flat. If anyone here runs into this issue and can't find one of the old disconnectors, PM me and I'll give you my spare.