snap cap

noun2

1. •
   A cap or cover that snaps into place.

   • Development of the snap cap for Bufferin pinpoints the Bristol-Myers Products approach to these problems. — 1966
2. •
   A dummy round of ammunition used to check ammo feed and other mechanical problems.

   • 1187. B. Lilly. Improvements in the construction of "snap caps" or "nipple protectors" for firearms. Dated May 12, 1863. — 1863