The Proof and Testing of Firearms

Purpose and brief history

Proof is the compulsory and statutory testing of every new shotgun or other small arm before sale to ensure, so far as it is practicable, its safety in the hands of the user. Reproof is the similar testing of a small arm which has previously been proved. Both necessarily involve the firing through the barrel of a considerably heavier load than is customary in the shooting field, thereby setting up pressure and stress on barrel and action much in excess of the pressure generated by standard load cartridges. Such pressure should, and is intended to, disclose weakness in guns, whether new or used, for it is preferable that weakness be found at a Proof House rather than in the field, where personal injury may result.

The Law

The present law on the subject is to be found in the Gun Barrel Proof Acts 1868, 1950 and 1978 and various Rules of Proof, but particularly those of 1925, 1954, 1986 and 2006 when the metric system of measurement was introduced. Copies of the Several Acts and of Rules of Proof of 2006 may be obtained from either Proof House.

The Proof Acts

The provisions of the Acts apply to all small arms, whether of present use or future invention, within certain fixed limits of bore size and projectile weight (with the exception of some military arms made for the use of H.M. Forces). Air guns, are exempt from proof by Proof Act.

The Proof Acts lay down that no small arm may be sold, exchanged or exported, exposed or kept for sale or exchange or pawned unless and until it has been fully proved and duly marked. The Maximum penalty is £5000 for each offence, but with provision for higher penalties where, for instance, the sale of a number of guns constitutes one offence. Alteration to or the forging of proof marks is a more serious offence.

Arms previously proved and bearing apparently valid proof marks are deemed unproved if the barrels have been enlarged in the bore beyond certain defined limits or if the barrel or action has been materially weakend in other respects.

The offence in dealing in unproved arms is committed by the seller, not by an unwitting purchaser.

Foreign proof marks

Until June 1980, there was reciprocal agreement for recognition of certain foreign proof marks by international agreement. Since June 1980 when the United Kingdom became a member of the International Proof Commission ( the CIP), the United Kingdom has recognised all the proof marks of other member nations and reciprocally they all recognise United Kingdom marks.

Rules of Proof

Rules, Regulations and Scales of Proof, a schedule to the Proof Act, are the working instructions of the two Proof Houses. The rules specify the pressure to be used in proof, standards of view and the marks to be impressed on guns which pass proof, together with much detail as to bore and chamber dimensions, proof and service pressure.

The latest Rules of Proof, those of 2006, were approved by the Secretary of State to come into force on the 1st August, 2006, but proof under earlier Rules of 1875, 1887, 1896, 1904, 1916, 1925, 1954, 1986 and 1989 remains valid provided that the barrel or action has not been materially weakened or altered so that it no longer conforms with the proof marks.

Submission to proof

Any individual may submit arms for proof or reproof direct to either of the Proof Houses, but it is more usual and generally more satisfactory for all concerned that arms be submitted through a gunmaker.

Primarily this is because the majority of old guns require attention prior to proof. Proof regulations require that shotgun barrels shall be “struck-up” and smooth and that insides shall be clean. Pitting should be removed so far as is practicable, bulges knocked down and dents raised. Actions should be in good, safe working order and tight on the face to resist the increased strain of proof pressure. Since stocks, and particularly those with unusual “bend” or “cast”, are not designed to withstand the heavy recoil of proof, it is customary for the wood to be removed. Indeed, the Proof House do not accept responsability for damage to stocks resulting from proof.

It will be apparent that to fulfill these requirements the preparation necessary will best be undertaken by a gunmaker who is accustomed to submitting to proof.


In the event of a proof reject, or failure to withstand the proof test, guns may be repaired if possible and resubmitted. On final rejection, that is when the submitter accepts that further attempts at repair are unlikely to succeed, the existing proof marks upon the barrels and/or action will be defaced or barred out. It is unlawful for a weapon to be sold with defaced proof marks, except where later reproof marks have been impressed. It is recommended that such a gun be deactivated, to ensure that it can never be used by some person unaware of its unproved condition.

Examples of proof marks impressed by the Birmingham Proof House

Proof Testing of Ammunition and Explosive Powders for the Trade and Home Loader.

Under the rules imposed on Proof Houses in Europe and other countries, set by our governing body, the Commission Internationale Permanente (CIP).

Headquarters in Liege, Belgium - cartridge manufacturers are required to provide samples of their products to be subjected to test by the Proof House and, if satisfactory, may carry the Proof House and CIP mark (see right).

Although the same rules do not apply to home loaders, given that their products cannot be legally sold, in the interests of safety the Proof House affords those parties opportunity to batch test their ammunition to ensure that the associated breech pressures and velocities are within acceptable standards. By so doing it removes the potential for weapons being damaged, thereby injuring the user or, even worse, innocent bystanders. Previous tests of this nature in the past have indicated the poor standards adopted by such parties and the lack of uniformity between rounds of ammunition.

Similar tests can be made on various powder batches or powder types.

The ammunition is tested in the Proof House Laboratory using modern test guns which are linked to a computer to provide graphical presentations.

Please write, fax or telephone for details.

Proof House and CIP mark