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A Proof Mark Primer, 1891-1939
By Steve Meyer, German Gun Collectors Association
Unravelling the history of a German sporting gun or rifle is often a difficult proposition. With the exception of a few larger makers like J.P.Sauer, Merkel and Krieghoff most records are lost and only the guns themselves bear testimony to the history, workmanship and artistry of German gunsmiths.
Fortunately, one source remains to us, and that is the marks on the guns themselves. Beginning with the first German proof law that came in to effect in the early 1890s, all sporting firearms produced in Germany were required to pass rigorous strength and safety tests at a government regulated proof house. Over the years German proof laws, like those of other European countries, were revised to cover changes in gunpowder, materials and design, and changes in proof law and the marks prescribed can be very helpful in tracing date of manufacture, chambering and originality.
I won't attempt to cover the all ins and outs of German proof law here in detail, but there are a few bits useful for dating that frequently come in handy.
Guns and rifles built in Germany and the German principalities before the 1890s typically did not carry proof marks, but the 1891 proof law 'grandfathered' these arms by mandating that they be submitted to the proof house and marked with a crown-over-V, the V standing for vorrat or 'on hand'. Any German gun or Rifle carrying a crown-over-V dates to 1891 or earlier.
Marks showing crowns over the letters B, U, (proof approved); G (rifled barrel), S (smoothbore) and W (choked barrel) span the period from the first German proof law until 1939, but there are other marks usually present that can narrow the date range greatly.
Rifles marked with only an indication of powder charge and bullet type as shown below date to 1912 or before:
2,67 g GBP
St m G
These marks show 2,67 grams of Gewehr Blättchen Pulver (military flake powder) and Stahl-mantel Geschoss (steel jacketed bullet). Other possible types are "K m G" for Kupfer-mantel Geschoss (copper jacket) and "Bl G" for Blei Geschoss (plain lead bullet).
After 1912 marks were changed to show just bullet type and bullet weight as in:
St m G
12 g
usually accompanied with a crown-over-N or the word Nitro, specifying smokeless powder.
Shotgun barrels of this era will sometimes be marked with a powder charge over a shot weight, but the style of the marks didn't change markedly over time. Note, however, that some will be marked with the high-pressure proof load, while others will be marked with the standard service load. Shotgun barrels will also be marked with the gauge designation in a circle and, unless they are specifically stamped otherwise, will be chambered for 65mm or 2-1/2" shells. As an interesting sidelight, I have seen more than one German double rifle advertised that bore crown-over-W marks on the underside of the barrels. A closer inspection revealed that their rifled barrels had been sleeved into the shotgun barrels or block and they were in no way original, or perhaps even safe. Caveat emptor!
The most frustrating but perhaps the most useful marks of the 1891-1939 era are the various sets of just numbers often present. The two most common sets of numbers applied were bore dimensions and actual proof dates.
Rifles from later in this era are sometimes stamped with a bore (not groove) diameter in milimeters, the most common being 8,8mm for one of the 9,3mm cartridges and 7,7mm for one of the many 8mm cartridges.
Many earlier rifles will be found with numbers indicating the "gauge" diameter of the bore (not groove). For instance 108/49 would indicate a bore diameter from .350-.359" and hence likely to be a 9,3mm chambering of some kind, while 172/28 (.300-.309") would indicate an 8mm of some kind.
See table below for rifle gauge numbers.
The other set of numeric marks often found on both rifles and guns is the actual date code of proof. The style of these numbers can easily be confused with the gauge markings described above, so be aware that both possibilities exist. Typical date codes will be three or four digits signifying month and year, as in 513 for May, 1913, or 1127 for November of 1927. Sometimes there will be a dot or slash between the month and year, but most often they are just run together. Often the date code is above a line, with another number below the line. The number below the line is that gun's actual entry number in the proof house records for that month and year.
All of the preceeding notwistanding, there is a great deal of variation in proof marks of German guns and entire books have been written on the subject of proofs. With so little information yet discovered about so many German makers, a working knowledge of proof marks can be your guide to the hidden histories of German sporting arms.

Rifle Gauge Table
A brief table that is pretty helpful for pre-WWI German rifles shows the use of fractional 'gauge' numbers for barrel diameters. This was largest plug gauge diameter that would fit in the bore. The British proof law of 1868 had set up standard gauge sizes from .300" (172.28 gauge) to .450" (51.05 gauge) in .010" increments in the same sense that a shotgun bore is gauged, by the number of round lead balls of that diameter that make a pound. The Germans adopted this somewhat awkward system as well.
Gauge - inch
51.05 - .450
54.61 - .440
58.50 - .430
62.78 - .420
67.49 - .410
72.68 - .400
78.41 - .390
84.77 - .380
91.83 - .370
99.70 - .360
108.49 - .350 very common on 9,3mms
118.35 - .340 somewhat common on 9,3mms
129.43 - .330
141.95 - .320
156.14 - .310
172.28 - .300 very common on 8mms
These are most frequently seen with a / instead of the decimal point, as in 172/28 or 84/77

I think that Casper is right about Buffalo horn as my knowledge of horn gun furniture is very slight, it not being a normal British gun material except for fore-end caps and sometimes grip caps. I do not agree with the idea that this gun was repaired or reproofed after 1950 as the data from which this was concluded is very far from complete and does not go back to 1891 when German Proof Laws were introduced. The retro proofing of guns made before 1891 will have been a matter similar to the Proof Acts in England which did not disallow the ownership of an unproved or out of proof gun but did strictly forbid the sale or transfer of such a gun to any person who was not a Registered Firearms Dealer. A dealer receiving an unproved gun was obliged by law to have it proofed before he could sell or transfer it to any person who was not also a registered firearms dealer. The 1891 German Law will have been made in the full knowledge of the practice in those other European States with such laws, of which the English were the longest established (1620).