proof charge

noun2

1. •
   A charge of powder and ball, greater than the service charge, fired in an arm, as a gun or cannon, to test its strength.

   • Amd. the official "Extracts of Artillery Proceedings" tell us, 4:3:72, tha the Superintendent, Royal Gun Factories, "proposes tha the proof charge for the 12-inch gun of 35-tons shall be 115 lbs. — 1873
2. •
   A small charge used to test or measure the electric field created by other charges.