9 mm brass snap cap insert

press this insert into a NON primed and resized or Unfired casing

do not use with a primed casing or a non sized casing
not responsible for what you do with this

it is a tight fit and may need to be adjusted based on printer, filament, casing, chamber

it is normal to shave a little off as you press it into the chamber, I sometimes also make tpu primers if you want to "protect" the firing pin... I think its totally unneeded but a nice touch