This is to be used while cleaning to catch excess solvents/oils. Any other use should be confirmed to be legal before use. I advise you to follow any applicable laws where you reside.
I recommend printing a few layers of the interfacing end to test the fit over the sight post (see last image). This is a friction fit design. I made adjustments for shrinkage and my slicer settings. Your mileage may vary.
I printed with the muzzle end on the print bed. I used .2mm for my layer height. There are a few corners that are a bit steep but it seems printable/functional.
Use 2" PVC sleeve to reduce print time, material use, and add rigidity/strength.