The date bands would be from July 23rd, 1893 for the 4000 Atmosphärenpulver Test to the proof rules change in either 1910(Zella-Mehlis) or 1911(Suhl). If you have shown all the stamps, then it passed thru the Suhl Proof Facility circa 1911 when the bore diameter changed from bore gauge to mm. The calibrator @ the Suhl Proof Facility may have used the mm stamp a little earlier that 1911, so the bolt gun platform would date to that period. If later than 1911, it would wear a stamp of bullet type over weight.
The 4000 Atmosphärenpulver Test(58,800 lbs/in^2) was a new fangled test on July 23rd, 1893 and used a Special Super Strong Pulver from Spandau. The stamp of >>G.B.P<< is most easy to decipher being >>Gewehr Blättchen Pulver<< which is a Military Rifle Flake(smokeless) Powder. The Bullet used in Proof was a standard jacketed projectile with 0.2mm >>Windage<<. I think the Belgians used 0.6mm & I'll have to check that. But proof of rifled barrels proved w/ semi-smokeless / smokeless was a crap shoot and German Proof of Tubes from the get-go in 1891 w/ Black Powder was the same as the mechanics complained of all the burst & bulged barrels as Germany used a heavier proof load than all other countries w/ Proof Facilities. Now comes the 4000 Atmosphärenpulver Test as the German Proof Facilities devised their own plan seeing a double load of Gewehr Blättchen Pulver would have shocked everyone, including the tube so many times the tube was stamped w/ a load less than the true service load. I could go on if anyone is interested........
Now on to the puzzle: >>S.G.<<
>>On the other hand, the not commonly seen "S.G." might have stood for Spitzgeschoss, and hence may have indicated an 8mm barrel for the so-called "S"-Patrone (wider bullet, wider chamber neck, maybe appropriately reamed leade, while the lands and grooves however might not be different from the M/88 pattern).<<
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Raimey
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