I have a full size P320 in 45.

I am wondering if the 10mm magazines fit the grip module on the 45?
Or does fit smaller cartridges?

So if anyone has a 45 and 10mm can see if the magazines are swappable, 10mm into .45?

Cause if they are, I just added a caliber to my 320.

I am talking about getting a slide assembly, no hackery, Real Sig stuff.

Thanks for looking

The magazines will fit the mag well yes.

The FCU unit are interchangeable among all calibers.

It’s my understanding that the 45 and 10mm grip modules are a different dimension to accommodate the larger mag.

I understand that the P320 .45 magazine metal "shell" is the same size as with the P227 .45 magazine, dunno if the magazine catch hole is at the same height location.
(Some details around whether mag says ".45" or ".45 ACP" may make the difference. Haven't had all the pieces around to research this yet).