Summary

The original design was too weak and self destructed but the geometry was correct for the locking ribs. I filled in the open space behind the slide to give it much more strength, changed to a ring design for easy grip and shortened the overall length. The fit is VERY tight to keep if from flying off with recoil. You may need to sand or relieve the lower edge of the curve where it contacts the back edge of the slide to get it installed.

I used PLA because that is all I had available, but a stronger material would probably be better. I didn't have the CAD files so I had to piece it together in TinkerCAD. There were a couple of data errors in the original STL, but it still prints fine.