Put pause in print at Layer 158 if printing in 0.2, insert 4 of the reflectors and resume print.
Hole ID is ~8mm so it might work for 32acp other wise .22 or others
Print Threads down, 100% Infill, PLA+ or better.
Use a 3/4-10 to 1/2-28 adaptor and epoxy it in
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Reflectors: https://www.temu.com/goods.html?_bg_fs=1&goods_id=601099620508360
Size: inner hole 7.94mm
Diameter 27.7mm
Height 20.09mm
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UPDATE:
    Small change, added a 1mm area at the muzzle end for the print, you will need to poke it out or just shoot it out once done to clear it. Didn't want the printer to try and print in the air.
    Also you will need to file down the tabs on one of the "reflectors" that will be the top most one in the stack. I did have a  small grove just to sit in but it would make printing the top muzzle hard to print