Guncraft

Old doubles rarely come with operators’ manuals. How often do we wish they did? Who hasn’t had questions about an old double’s condition and safety, especially about what shells can be safely fired through a gun that could be a century old, maybe older?

If a gun originated in England or Europe, however, it will have operating instructions of sorts—its proof marks. These series of impressions, usually located on the action and barrel flats, certify that at some time in its life the gun was tested at a proof house to reveal any structural weaknesses. The markings are “proof” that it passed those tests. The proof process consists of firing heavier-than-normal loads through a gun and then carefully examining the gun to ensure that the elastic limits of the metal in the barrel and action have not been exceeded. The specific proof marks on a gun also will reveal important clues about the gun’s original specifications and the uses its maker intended it for. These two factors—and the gun’s current condition—will in large part determine the sorts of shells you should use in it.

To the uninitiated, decoding the world’s proof marks is unfortunately a cryptic task at best—and even those with working knowledge will admit the subject’s complexities. Americans, with no government-sanctioned proof houses to turn to for advice or guidance, are at an especial disadvantage.

No article of this brevity can do justice to a subject so vast, but the novitiate can gain some understanding of what sorts of shells are appropriate to use in an older British double by examining the issue of pressure—in this case using England’s Rules of Proof as a guide, specifically key tenets of the Rules of Proof of 1925 and ’54. Though these Rules have since been superseded, their principles regarding safe pressures for fine doubles retain relevance.

Rules of Proof are the working instructions for Britain’s two proof houses. Authorized by the Gun Barrel Proof Acts—which are acts of Parliament—the Rules specify in detail how guns are to be proofed and marked. In addition to certifying that a gun has at some time passed proof in either London or Birmingham, the marks—depending on the Rules in effect when impressed—will specify matters such as the gun’s nominal gauge, its nominal bore diameter, its chamber lengths, what sorts of propellants it was proofed for, and either its intended service loads (or service pressures) or the pressures the gun was proofed at.

The Rules never have been cast in stone—they have been revised as circumstances demanded by proof authorities. Through most of the 20th Century these were driven chiefly by technology—the interplay between advances in propellants and cartridges and improvements to the materials used in gunmaking.

The end of the 19th Century, for example, saw the appearance of various smokeless powders as well as the gradual supplanting of Damascus barrels with those of fluid steel. World War I (and II) drove great improvements in metallurgy, with subsequent alloying of nickel, chrome, vanadium and molybdenum increasing the tensile strengths of steels. Concordant with better steels have come vastly improved powders —specifically progressive (slow-burning) powders that allow heavier shot loads to be propelled without increases in peak pressure.

  The Rules of 1954 replaced those of 1925, which had replaced those of 1916, which had replaced those of 1904. And back it went. Those of ’25 provide important perspectives necessary to understand those that were to follow. For the first time the actual length of the chambers was marked, and for the last time the weight of the shot load of the normal service cartridge was impressed (the latter having been a practice since the Rules of 1896). To use the case of the 12 gauge, a British game gun with then-standard 2-1/2" chambers was proofed and marked for a service load of 1-1/8 oz; a 2-3/4" gun for 1-1/4 oz; and a 3" gun for 1-1/2 oz.

It’s important to understand that in Britain there had been an immutable relationship between cartridge length, chamber length and shot load. For example, through the ’25 Rules, no 12-gauge 2-1/2" gun would have been proofed for a greater payload than 11/8 oz with either blackpowder or smokeless “Nitro” shells. (During World War I payloads in 21/2" shells actually dropped to 1 oz or 1-1/16 oz to conserve lead, but regardless none would have exceeded 11/8 oz.)

The weight of the shot load played a vital role in helping regulate pressures during an era when various blackpowders and early smokeless powders coexisted in use. “The markings on the 12-bore game gun implied that the shot load should not exceed 11/8 oz,” wrote then-Birmingham Proof Master Roger Lees in a January 1955 article in The Field explaining the new Rules of ’54. “Its real meaning was this was the maximum shot load to be used so long as the standard load of black powder or its equivalent in smokeless powder was employed.”

But Britain’s proof authorities had not anticipated cartridges like the Maximum, introduced in the mid-1930s by Eley/Imperial Chemical Industries (ICI). Popular with rough-shooters, the Maximum packed 1-1/4 oz of shot into a 2-1/2" 12-gauge cartridge (the Maximum’s load was later reduced to 1-3/16 oz).

An extra 1/8 oz may not sound like much, but it upended proof’s proverbial applecart. Now a 2-1/2" cartridge was available with a shot load that exceeded the 11/8 oz limit to which 21/2" guns were proofed and marked. The proof houses viewed the Maximum as setting a potentially dangerous precedent that the ammunition industry at large would follow.

Eley, in fact, used newly introduced progressive powders in the Maximum so that it actually developed no greater peak pressures than standard 1-1/8-oz loads—making it safe for in-proof 2-1/2" game guns. To the proof authorities, however, that was not the point. Charles Greener (of W.W. Greener), then chairman of Birmingham’s Proof House Guardians, called the Maximum “illegal;” ICI threatened a lawsuit in response. After consulting with lawyers, proof authorities backed down, but the stage was set for drafting new Rules of Proof.

New Rules, however, would have to wait. The Depression, World War II and Britain’s subsequent economic dislocation—indeed, the funk into which the post-war gun trade sank—all conspired to delay their drafting for nearly 20 years.

The Rules of 1954 were enacted in October that year and became effective February 1, 1955. They remained in effect until the Rules of 1984, making them the longest running of any of the 20th Century’s. They remain recognizably “modern” in the sense that they codified proof principles still in use today, and for the layman their clarity makes them the easiest of any to understand. As Roger Lees noted at the time: “In the English speaking world they will be far better understood and appreciated, for they are comprehensive, unambiguous and written in a language intelligible to all.”

The number of markings was reduced and simplified, and for the first time the nominal bore size was marked as a decimal part of an inch—12-gauge now was shown as .729" (as measured 9" from the breech), which replaced the more coded system of marking bore diameter with gauge sizes or fractions thereof (see chart p. 108). Excessive bore enlargement (to remove pitting, rust and so on) is one of the most common ways in which a gun is taken out of proof. The decimal system allows anyone with a bore gauge to easily check this. Under the ’54 Rules (and those preceding them) a 12-gauge could be enlarged by .010" before going out of proof. For example, a 12-gauge proofed at .729" would not be out of proof until its bore reached .740". It then would have to be re-proofed if it were to be legally sold in Britain. A gun remains in proof, incidentally, so long as the parameters set down by the original Rules under which it was proofed have not been exceeded or the gun subsequently weakened in specified ways (such as cracks in the action, gas welds to the action or barrels, failure of the brazing of the barrel lumps, among others). But if a gun is re-proofed under new Rules, the parameters established by the latter take precedence. Remember: To be legally sold in Britain a gun must be in proof at the time of sale. If a gun has been re-proofed, it will have a special marking that denotes this. It also will have additional impressions from the Rules it was re-proofed under, as well as those of its original proofing.

The most important result of ’54, though, was the explicit marking of the mean service pressure of cartridges intended for the gun rather than marking their maximum shot load. Progressive powders—and cartridges like the Maximum—had rendered the latter practice obsolete.

“Since the powders and loads now available giving safe pressures are many and varied, no proof marking of load alone can cover the possible range of loads,” explained Roger Lees in The Field. “It is considered that the proof marking of highest mean service pressure is measurable and can be expressed in terms that are universally understood.”

“Mean service pressure” is the average pressure of the normal service load intended for a particular gun. This was expressed in English long tons and so marked on the barrel flats (see markings chart, p. 106, and pressure chart above). Under the rules, ammunition also was marked for pressures so that shooters were assured they were buying cartridges that developed pressures appropriate per the chamber length of their guns (see pressure translation chart above).

Though the ’54 Rules spelled out for the first time that definitive proof was to be 60- to 80-percent greater than normal service pressures, authorities emphasized that these pressures would not set up stresses greater than those of proof loads from earlier in the century. “The proof loads now set down in writing [in ’54 Rules] are almost in every instance the proof loading in use under the 1925 Rules,” Lees wrote. “In general it may be said that under the new Rules of Proof no arm will receive a more severe proof than hitherto. Some, such as the 12-bore 2-inch and 4- and 8-bore guns will now receive a less-severe proof than they received heretofore.” Lesser proof pressures were possible in some cases, Lees went on to explain, because of greater understanding of the ballistics of these loads.

The world of proof, gunmaking and ammunition has changed dramatically since 1954. Britain joined the Commission Internationale Permanente pour l’Epreuve des Armes à Feu Portatives (CIP) in the 1980s, and new Rules were adopted in 1984, ’86, ’89 and 2006. Proof marks now are expressed in metric rather than Imperial measurements, and the pressure markings on guns are now proof pressures, not service-load pressures. The tools used to measure those pressures also have changed, from crusher gauges to more-accurate transducers. Nontoxic shot and a global proliferation of new loads, many of them having high pressures, have muddied what was once an easily understandable relationship between cartridge size, chamber length and pressure.

Yet the Rules of ’54 and its Imperial predecessors remain as instructive as ever in certain regards. For one, the proof marks of this era will provide a clear indication of a gun’s original purpose. English makers traditionally built their guns around specific maximum loads: A 12-gauge game gun normally will have 21/2" chambers and bear proof marks for 1-1/8-oz loads (1925 Rules and earlier) or three tons of pressure (1954 Rules); a heavier pigeon gun will have 2-3/4" chambers and have marks for 1-1/4-oz loads or 31/4 tons; a stout wildfowler will have 3" chambers and have markings for 1-1/2-oz loads or 3-1/2 tons. Remember that these early shot-load markings should be thought of as an alternative expression of suitable service pressures (as the ’54 Rules would later codify).

With this in mind, the shooter has a number of options available when picking appropriate loads for the gun in question. Granted, this is a complex enough issue to warrant an article in itself, but for starters the most conservative approach for Americans is to shoot CIP-approved loads from the same country of origin as the gun, choosing shells based on appropriate chamber sizes and on the markings on the ammunition box that indicate shell specifications.

  Another alternative for Americans is to shoot appropriately sized, low-pressure shells as made by specialty US-based producers such as RST/Classic Shotshell Co. or Polywad. Both companies specialize in producing a wide range of shells for the vintage-gun market. Neither publishes pressure figures on its boxes, but they often will supply them on request. (Federal also currently markets a low-pressure vintage-gun load through Midway USA.) Yet another alternative is to reload low-pressure loads. I am once again giving short shrift to a complex subject, but bear in mind that because of differences between the ways pressure is measured by CIP and by America’s Sporting Arms and Ammunition Manufacturers Institute (SAAMI), there are no direct mathematical conversions from one pressure measurement to the other. It is therefore incumbent on the reloader to very much err on the side of caution when it comes to pressure when working up suitable loads.

Perhaps most enduringly, proof marks are your guide when comparing a gun’s specs as it left the factory to the condition it is in today—particularly in regards to its bore diameter and chamber lengths. It is a caveat worth stressing to have any old gun vetted for condition and safety by a competent, qualified gunsmith before firing, regardless of the pressures of the shells you use.

The Rules were written to be followed.

Author’s Note: One of the best primers on proof is Notes on the Proof of Shotguns & Other Small Arms, available for £6 (about $12) from the Birmingham Gun Barrel Proof House, Banbury Street, Birmingham, England, B5 5RH; www.gunproof.com. The Website is also of interest and has other resources on British proof, including topics such as steel shot and re-proofing memorandums. Special thanks to Peter Powell, former Chief Guardian of the Birmingham Proof House, and Roger Lees and Roger Hancox, Birmingham Proof Masters past and present, for technical assistance with this article.