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Technical aspects of shooting

GUN PROOF, CARTRIDGE  SERVICE PRESSURE, AND SAFE SHOOTING

“Is my gun safe to shoot lead or non-lead cartridges?” is a question every shooting person should ask himself or herself frequently, especially when acquiring a new gun or using different types of cartridge.

But, there are so many terms and units used, which also keep changing, that confusion and uncertainty often arise. Adding to the complications, lead shot has been joined by steel, bismuth, tungsten-based and other shot types, with the International Proof Commission (CIP) regulatory system affecting our use of them in different ways.

Shotguns clearly have to withstand the gas pressures generated within their chambers by the burning of the powder of each fired cartridge. The gun is proved by firing, and surviving, two or more proof cartridges which generate higher gas pressure in the chamber than the maximum cartridge service pressure allowed for that type of gun. Each cartridge designed for use in that gun (mainly by matching cartridge length to chamber length) must generate a service pressure well below the proof pressure of the gun.

Regulation

In this country our gun safety is controlled principally by the Gun Barrel Proof Act of 1868 and subsequent Acts in 1950 and 1978, as expressed through Rules of Proof, primarily of 1925, 1954, 1989 and 2006 (shortly to be revised in line with a new proof act).

The 1868 Act requires that no gun can be legally sold, exported or exchanged unless it is in proof. Once a gun has been through the proof test, including visual and dimensional inspection, it is stamped on the barrel to confirm the fact, and to show its user it is safe to fire cartridges designed for that bore, chamber length and type of gun.

In several European (and a few other) member countries, CIP has established proof houses in order to ensure shotguns that are made within or are imported into member countries can safely withstand the service pressures generated by the cartridges designed to be fired through them. This is enforced by national law of the member states. For many years there has been international agreement that proof marks from various proof houses around Europe would be acceptable within all participating countries.

For long “Standard” and “Superior” were the main types of gun proof, relating to lead shot. To accommodate steel and similar types of shot there is now “Steel” proof.

The presence of a proof mark is no guarantee a gun is still in proof. If there is any doubt, seek advice from a reputable gunsmith.  Remember, to sell an out-of-proof gun is a criminal offence.

Proof marks

For lead shot use, a proof house mark confirms the barrel has been proved (for the chamber length etc of the gun). A stated pressure figure may confirm the pressure at which the barrel was successfully tested. But it may not and great care is needed. Is the stated pressure the level at which the gun was proved – or is it the service pressure of cartridges which the gun is deemed safe to fire? Furthermore, a stated pressure figure may have been produced by different measuring systems used over the years and so its meaning may not be clear.

For example, a gun made before 1984 most likely will have the cartridge maximum service pressure stamped on its barrels, whereas after that year the stated pressure most likely will be the gun’s proof pressure. This is a crucial difference as it means that, if the stated pressure figure is interpreted as the service pressure for suitable cartridges, when, in fact, it is the pressure at which the gun was proved, then cartridges could be fired through the gun which generate chamber pressures close to or even over the gun’s proof pressure, thereby risking serious damage to the gun and its user.

For steel/steel-like shot, a different process is involved. A standard or superior/magnum-proved gun can fire Standard steel shot cartridges, subject to conditions. To fire High Performance steel, it has to have passed Steel Shot proof, a more rigorous test of the gun’s ability to handle the different pressures (same as high performance lead) and shot hardness of steel/steel-like shot cartridges. A gun successfully passing Steel Shot proof has to be stamped with a Fleur de Lys on its barrel.

Pressure marks on a barrel should not be relied upon – only CIP’s Standard and Superior proof marks or the Steel shot mark are reliable. On older guns the marks of CIP proof houses represented standard or superior proof – pressure values (as earlier used by UK proof houses), should be seen as ‘symbols’ defining standard or superior proof. See table below.

Information and guidance

BASC has been working on a detailed explanation of how the gun proof process and cartridge testing system has worked – and changed – over the years. It will cover the way pressures are measured and how they are reported. It will help understand how different pressure units used over the years, caused by different measurement systems, relate to each other. It will fully explain how non-lead shot cartridges, including Standard Steel and High Performance Steel differ and how they are used safely. It covers 12 and non-12 bore guns and cartridges.

BASC is working closely with the Birmingham Proof House on this material. Once it is completed it will be made available here on this website.

In the meantime, and to introduce complicated subject matter in a simplified way, the following table of proof marks used in this country under the CIP rules is provided. This will be followed, once they have been obtained, by the proof marks used by all CIP member countries to help clarify
the proof status of any gun bought or acquired from outside of the UK.

CIP Standard & Superior Proof Marks

CIP Standard Mark
CIP Superior Mark
CIP Steel Mark
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Table of equivalent Birmingham Proof Symbols-
(Including the above CIP marks introduced by Birmingham in 2014)

CIP
UK
-Birmingham
STANDARD
SUPERIOR
STEEL
2014
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2006
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1989
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1954
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Footnote:
This table shows changes in the basic marks relating to Standard and Superior proof since the 1954 Rules of Proof, and the introduction of Steel Shot proof in 2006. So, for example, if a gun shows the BNP mark plus 3 tons per square inch then it is equivalent to CIP’s Standard proof now. It also shows how the metric pressure units – bar – introduced in 1989, indicate Standard and Superior proof.

These marks and units, and other variants, will be explained in detail on this site in due course.

Updating this site

As the new information and guidance become available this site will be updated.

Advice

Please direct enquiries about these matters to:

BASC Firearms Department at BASC Head Office – 01244 573010 or firearms@basc.org.uk

Deputy Proofmaster, Birmingham Proof House – 0121 643 3860

Finally……

At any time if there is any remaining doubt about the proofing of your gun or suitability of cartridges to fire through it – check with a reputable gunsmith. If doubt still remains then have it re-proved to be sure it is safe to use with appropriate cartridges.

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