[HollowPoint]

You need the new hammer strut. If you're buying from HKParts, they have the wrong description on the old hammer strut. It is NOT the new-style strut.

ETA: Use the hammer strut that came with the other gun (USPt) and see if it solves your issue.

TooSixy, you are a brilliant man. It was the hammer strut and it is working like a charm. Thank you sooooo much for all of your help!