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The Gun Room

Oct 8, 2021

 Barrel Proofing

Dad and I were browsing the used gun rack at a big box store on a trip through Pennsylvania a few years back when we happened upon a double gun that caught our eye. The gun was a 12ga with light color walnut stock and forend. On closer inspection, we saw a moderate amount of hand-cut engraving, as well as hand-cut checkering on the buttery walnut stock. An older gun made in Europe, the tag read ‘BLNE’, as it is sometimes referred to in gun parlance or a boxlock non-ejector. We speculated on the country of origins and details of the gun’s specifications until we could get the attention of one of the clerks to ask if it was OK to take the barrels off the action and check the proof marks.

Spend any amount of time in a gun shop that deals with guns from Europe and you will inevitably hear someone say “check the proof marks”. This statement broadly suggests checking the markings on the barrel flats and action watertable(on a shotgun). These are the two areas that gunmakers typically apply stampings pertaining to original specifications of the gun like chamber length or choke. It is also the area where proof houses apply proof marks on a gun. 

Proofing is a type of (potentially) destructive testing whereby a firearm is discharged with appropriate dimension ammunition that has been overloaded with powder on purpose. Shooting a round overcharged with powder produces higher than normal pressure inside the barrels and action when the gun is fired. If the gun can withstand the increased pressure produced by an ‘overloaded’ round, it will withstand the significantly lower pressure of standard factory ammunition. Guns are measured before and after testing and fired remotely while being held in fixtures inside secured rooms for safety reasons. Proofing is a pass or fail test, there is no middle ground. Guns that fail may experience a bulged or split barrel, or in extreme situations, action failure can result in shattered parts.

Proofing firearms began hundreds of years ago in Europe(1637 in the UK) and continues to be conducted as described above. 14 countries in Europe have adopted standards laid out by CIP (think international proofing organization) which now dictate the pressures various firearms need to withstand to make proof.

Each proof house in Europe developed its own proof marks. These marks changed over the years and can help date a gun or determine a gun proofed with black powder or modern smokeless powder. Most European guns were proofed in the country in which they were made, or at least the country where they were assembled to the point that they could be shot. As a result, the proof establishes the maker’s country, and in cases where countries had more than one proof house, will determine which proof house the gun was tested in. For example, 6 different German proof houses are Ulm, Hannover, Kiel, Munich, Cologne, and Berlin each of which has a different proof mark.

Jumping back across the pond, the obvious question becomes, “Where are the proof marks on Granddad’s old Ithaca Flues?(insert any american gun name here)” Despite the fact that Europe developed a comprehensive proof testing standard, the United States has left that responsibility on the shoulders of the manufacturers, who for the most part, have held up their end of the deal. American shotguns and rifles are tested, though the extent of testing is left up to discretion. This is not to imply that American made guns are unsafe, but rather the imputis of burden is on the makers themselves to ensure the end safety of the user. Makers could test every gun, or simply choose random samples to test. And, in todays complex and advanced manufacturing facilities, there are a myriad of other tests that can be done to ensure the quality, durability, and safety of a firearm.

Back in the gun store in Pennsylvania Dad and I took a look at the markings on the double gun that caught our eye. Typically on the flat sections of the action and barrel you will find several different marks. The serial number, if the gun has one, will be located here. Usually it is stamped on both action and barrels of a shotgun, and can also be stamped into the forend iron as well as the forend and stock wood(though always hidden where you have to remove them to see the numbers). On fine guns, many parts are also stamped with the serial number or at a minimum the last three digits of the serial number. On guns where hand fitting is required, not all parts can be transferred between guns; this helps in the factory to ensure the correct internal parts stay with the action in which they fit. The importance here is taking note if these numbers are matching throughout the gun. Mismatched numbers indicates that the gun has been composed of parts that were not originally manufactured together, which in turn can affect the value of the gun.

After the serial number, we typically look for the proof house mark that indicates where the gun was proofed, and its country of origin. The gun in question possessed a LEG proof mark referring to the Liege Proof House in Belgium. Since there was no makers name on the gun, we were left to assume it was a ‘guild gun’. That is to say that it was a gun made by a variety of outworkers- the stock may have been made by one individual, checkered by another. The metal work done by yet another craftsman, and then the parts assembled. Guilds were frequently found in Belgium and Germany, though the idea of outworkers performing various tasks and sending parts back to the primary maker is commonplace in the gun trade.

The next significant mark found was a lion over a “PV” indicating a nitro proof. This is where the proof house markings come in- this nitro proof gives us a good reason to believe the gun will be safe to shoot with smokeless powder. It is not uncommon to see multiple proof house marks, and this is where a knowledge (or good book) can help. Marks changed over time, and occasionally you will see a gun that was originally proofed for black powder, that carries a second set of marks indicating that it was re-proofed for nitro powder. 

It is a requirement that guns be reproffed in Europe depending on what work is done to them. If a gun was orignally a 2.5” chamber, which is lengthened to 2 ¾”, the gun must be reproofed. The same goes for if a gun is sleeved- new barrels put on an old action. Flats on guns like this can seem a jumble of marks but they all tell part of the guns story.

Our gun was also marked with a 12 and a 70 in a circle indicating its 12ga, 2 ¾” chambers. Thinking in metric terms, 65 or 65mm would indicate 2 ½” chambers, with 70 or 70mm being the elongated 2 ¾”. Though those may be what some consider the important marks, there can be many more marks in these areas worth checking out. On the barrel, you will often find the choke designations - this gun had them as numbers- 18.3 and 18.4- metric bore measurements.

There are other marks like a star over a U, a script 3, double stamped numbers and more- these can be preliminary proof marks, final proof marks, controller marks, personal makers marks, or the individual at the proof house that tested the gun. There can also be a number in Kg or kilograms that indicates the weight of the barrels at the time of proofing.


Proof marks can be our best link to a guns history, much like a passport that helps reveal a bit about the gun and its past. They can tell where the gun came from, where it travelled in its lifetime, and so much more. They are certainly one of my favorite aspects of old shotguns and rifles. All in all the Belgian guild gun was well worth the $ paid and it is now living happily amongst the other guns on my rest farm for old shotguns. The lesson: a base knowledge of proof marks is a handy thing when assessing used guns and certainly helped solidify my decision to buy, rather than pass, this particular double.