British Stamp Proof Mark NP under arm with a sword

An English Probing Mark applied to a weapon, confirming the successful completion of Trials involving the firing of cartridges with a greater force than standard projectiles. It varies depending on the powder used in the test (black or smokeless, otherwise known as nitro) and the type of weapon on which it was applied.

Used in London from 1904.

Acknowledgment Type: A proof mark confirming the successful completion of a test with 30% more nitro powder than typical for the weapon.