So I'm needing some mags for my new HK Mark 23 and was wondering will my HK USP 45 mags work in a pinch if I change the floor plates or is the body,follower,spring different ?
Or is just the bottom floor plate different?



The left is a Mark 23 mag the right is a USP 45 mag.

Mk23 mags are different. They look really similar, but they are slightly different and they don't work.

If I remember right the Mk23 mags have longer feed lips. I'd have to check my Mk23 mags against my USP Tac mags when I get home from work.

You are correct, sir.  The OP is also correct in that the floor plates are different.

I have used Mark 23 magazines in my USP 45s with no issues.  I have not yet tried USP 45 magazines (with Mark 23 floor plates) in my Mark 23.  I have read that the USP 45 magazine bodies will work, but they are not optimal.  YMMV.

MK23 magazines are very similar but have longer feed lips and obviously a slightly different baseplate.  Supposedly they work ok if you swap the baseplate, but we can presume HK made them with longer feed lips for a reason, so stick with genuine MK23 mags.

MK23 magazines will however work perfectly in a USP 45, so if you add a Tactical down the line, you'll be all set.