You are mis-remembering, you may have replaced your USP mag release with an HK45C version, but not the HK45. They are different.Not questioning whether you're right, just curious:
I have replaced my USP mag releases with HK45 mag releases -- what is it about the USP releases that prevents them from going into an HK45?
Thanks! Glad I asked -- always good to learn.TooSixy and Ecuser have both made the correct replies.
Also, while the HK45c release will work on USPs, HK will tell you that it will void your warranty and it is only designed for the HK45c.
However, with the exception of FS models, many of us use the larger release successfully on the USP Compacts and the P2000sk.
The HK45 has an entirely different style of release that is unique to itself.