Inspired by strike industries plug but adjusted for 3d printing. Printed in two parts for max strenght. Insert may need a little trimming, for the best fit, then glue in. Hex hole accept 2.5mm hex wrench (after cutting off the L shape and leaving just the shaft). The idea is you can use the wrench as a takedown punch. Mine is also filed down on one side, to act as a flat head screw driver, to adjust Holosun red dot.

Printed in ASA for temp stability and strenght. PETG should be fine as well, PLA way warp in high temp. Print orientation as in attached image.