The English Proof Houses are the oldest in the world and have also been testing weapons without interruption since their founding.

A weapon proofed in GB with NC powder would normally have the mark NP or even the entire written word Nitro Proof.

For this reason, a rifle that has been proofed in GB and does not bear the typical marks is not to be described as nitro proofed and is therefore to be regarded as just a BP rifle.