Using weapon modification tables and crafting mods for guns 50 times will net you this trophy. If you find a weapon with a muzzle attachment already installed (for example I had a pistol with a bayonet) you can get this trophy in minutes by uninstalling the muzzle by clicking on "none". None requires no materials, then go back and reattach your muzzle. Keep going back and forth 50 times and you will have this. Takes four to five minutes.