Memorandum on black powder guns

​​Up to 1887 there was provision only for the proof of guns for black powder; but by that time the use of smokeless or nitro powders was commonplace. In that year a proof to cover their use, supplementary to definitive proof, was introduced. The service load of the powder intended for use, i.e. E.C. or Schultze, was then impressed on the barrel at proof. Under the 1896 Rules, proof to cover the use of nitro powders was still supplementary to the ordinary proof for black powder, but the words "Nitro Proof" were introduced as a proof mark.

The NP marks were introduced in 1904 but the nitro proof test remained optional until 1925, when new Rules of Proof made it obligatory. By that time most gun makers had been voluntarily submitting their guns to nitro proof for many years.

Except on guns proved since February 1955 the NP marks were always used in conjunction with the words "Nitro Proof". The black powder proof marks remain valid, and a gun bearing them may still legally be used with black powder cartridges, provided it has not undergone any alteration taking it out of the category and state in which it was originally proved. Such alterations include conversion to ejector, rebrazing the lumps, increasing the depth of the chambers to take a longer cartridge or the enlargement of barrels beyond certain defined limits.

A gun, through neglect or misuse, may become unsafe even in a short time, and a gun made over fifty years ago may be extremely dangerous.

Shooters are therefore urged most strongly to buy only guns bearing the marks of nitro proof and not to permit the use of nitro or smokeless cartridges in any black powder gun already in their possession, until it has passed the nitro proof. If owners wish to use such guns with nitro powders, they should send them to their makers, other gun firm or gunmaker for advice, estimate for preparation in accordance with the Rules of Proof, the carrying out of such work, and submission for nitro proof.

The charges involved must of course be paid whether or not a gun passes the proof test, but it is better that any weakness be revealed at the Proof House rather than in the field.

Muzzle-loading and black powder proved guns may be reproved for black powder. It will hardly be necessary to point out to members of the gun trade that neither their own interests nor those of their customers can be served by the sale of black powder guns which may have become dangerous. For many years some firms have not sold black powder guns and, in addition, will not do any work to such weapons except preparation for and submission to proof.

Such a policy may not be possible in all cases, but apart from any question of legal liability for repairs carried out, it is urged that there is a heavy moral responsibility to point out the age and condition of any of these veteran guns before accepting them for repair.

Muzzle-loading arms should never be fired with nitro powders.