doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Proof marks interpretation?

Raimey, once a gun passed the 1954-55 proofs, it would not be stamped "not nitro" or "black powder", because those marks are for guns to be used only with black powder. And since this one passed nitro proof from the metric era, I think it's safe to assume that it would have passed nitro proof under the 54-55 rules.

I don't think the subject longarm was Nitro proofed/proved until post 1989. I could easily be wrong, but post 1955 one could by special request have a longarm proved with black powder hence the stamps "Not Nitro" in London and "Black Powder" in Birmingham as well as the "Crown" over "BP". The stamps "NITRO PROOF" and "NITRO PROVED" were eliminated. Circa 1955 the resurection of black powder guns had not occurred and probably wasn't anticipated and at the time tubes destined to contain black powder pressure were proved with semi-smokeless. And this longarm was black powder proved in 1954-55 and Nitro proved post-1989 provided the "Crown" over "R" is coupled with the "bar" stamp.

Kind Regards,

Raimey
rse

Regarding post 1962 French proofmarks, which I'm sure had some English basis or influence, after provisional proof and upon demand, the proofhouse would add 0.1-0.2mm to the actual measured bore diameter and stamp it on the tubes/flats. And this is all centered around the 0.2mm or 0.008" tolerance which when met constitutes reproof. For the French it was in 1965 that the pressure designation was changed from Kg/cm^2 to BAR while the Brits made the jump to BAR in 1989 from the 1955 ton/in^2 = 2240 psi = 157.49 Kg/cm^2. So I don't know for sure who was leading the rules of proof horse.

Kind Regards,

Raimey
rse

The gun, if marked 'Not for Ball' means that it was first proofed between 1875 and 1887 and had some degree of choke. The word choke, which I can see on the barrels in the photo, tend to have been used after 1887 and before 1904 (odd that). It has had a recent re-proof for black powder with the original 2 1/2" chambers (65mm.), and then someone has risked it for nitro proof having had the chamber lengthened to 2 3/4" (70mm.). There will be a date code for when the re-proofing was carried out; this date code is in the lettering and now numbering contained within the little crossed sceptre mark (I can't quite make it out in the photo). The marks used at both British proof houses are now in metric and there appears to be nothing Continental, French, Belgian or otherwise about this gun. If you contact the Birmingham Proof House they should be able to fully explain the marks and to tell you what to look for to see if it is still in proof; I would suspect that it is o.k. as the last two sets of marks are quite recent in type. They should, with the help of the date code and gun serial number, be able to tell you the date it was tested and by whom it was submitted. Lagopus.....

Thanks again for all efforts in explaining the saga of this gun.

Raimey, you could be right about the post-54 black powder proof, but I'm not sure why it would have been reproofed at that time, if not for nitro. Maybe because the bore diameter rendered it out of proof? At any rate, the last proof is obviously for nitro, and after the chambers had been lengthened to 2 3/4".

I could be wrong too. But with the 1st 1875-1887 London marks on the tubes as a 20B, it would have noted that the 20 bore plug gauge passed the full length and I would say a pretty broad girth regarding the actual diameter. From the 1868 rules for rifled small arms, a 20 bore would have covered the 0.61" to 0.620" range(0.610"<20 bore<0.620") while as a reference the 12 bore is centered at 0.729" between 0.720" and 0.730"(0.720"<12 bore<0.730"). At the moment I can't find any inch equalivent bore diameters(non-rifled) for the 1875-1887 period. So by the 1955 rules the actual diameter of a 20 bore would have been more precisely defined and this fact along with wear would have put the diameter of at least one tube outside of 0.2mm. Also, the point for measurement was changed from full length to 9" from the standing breech. But I think previous marks were still honoured/valid unless there was some alteration and the longarm was in a diffent state than when originally proofed/proved. And it was probably time for a baseline or a benchmark to begin to compare the diameter for the 0.2mm tolerance.

Kind Regards,

Raimey
rse

Based on this info, what would be the smallest bore diameter to call it "out of proof"?

<.602" and >.628". Early on I think if the tubes were in the rough, then the proofhouse allowed a little allowance maybe more than the 0.1mm to 0.2mm. I'm curious what your wall thickness are?

Kind Regards,

Raimey
rse

The thinnest is 23 thou 9" from muzzle.