doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com "In" and "out" of proof?

Depends on the tensile strength of the barrel steel and the intended load.
Twist and Crolle Damascus: about 55,000 psi
Winchester Standard Ordnance and other "cold rolled" Bessemer/Decarbonized steels: 60,000 psi
c. 1900 �Fluid Steel� (Siemens-Martin & Krupp Open Hearth Steel AISI 1021-1034): 75,000 � 85,000 psi
Krupp Fluss Stahl (Homogeneous Fluid Steel) was introduced about 1890 and by reported composition was similar to AISI 1045 which has an industrial standard tensile strength of 85,000 psi.
AISI 1040 (and modified), 4140 Chrome Moly (not used until after 1930) & Bohler �Blitz�: 95,000 - 100,000 psi
Winchester Nickel Steel and Marlin �Special Smokeless Steel�: 100,000 � 105,000 psi
Remington Ordnance Steel: 110,000 psi
And the really good stuff
Krupp �Nirosta� (1912 patent NIchtROstender STAhl 21% Chromium / 7% Nickel Stainless Steel introduced in 1913): 114,000 psi
Winchester Proof Steel (probably AISI 4340) introduced in 1931 for the Model 21: 115,000 - 120,000 psi
Krupp Spezial Gewehr Lauf Stahl (1895 �Special Gun Barrel Steel�): 138,000 psi
Bohler �Antinit� (Rostfrei Laufstahl chrome-molybdenum-vanadium introduced 1912): 138,000 psi
(NOTE: the tensile strength reported is for "cold rolled" barrel steel; all can be heat treated to much higher tensile strength for different applications ie. rifle receivers)

Courtesy of Hugh Lomas for English 12 bore Game guns with pre-1925 Proof: Chamber immediately prior to forcing cone - .105�

Factory original 20 and 16 gauge small frame guns with Damascus barrels however may have a wall thickness of .090� at the end of the chamber, and .020� in the distal third of the barrel, making it critical to use loads that match the ballistics of those originally intended for use in the gun.

It is my opinion that any but obvious superficial pitting (since it is impossible to accurately measure the wall thickness at the bottom of the pit) at the end of the chamber with borderline wall thickness makes the barrel unusable (without the use of chamber inserts)

OK one more question for the 1868 rules of proof experts. I have a gun made in 1872 and London proofed, marked 11, and it measures .779 all the way down both barrels. Is it out of proof? What other conclusions can be drawn from these facts?

11 gauge =.751"; 10 gauge =.775". In "London" its Out of Proof.
In NC not as long as it has adequate wall thickness. If you choose to sell it in England it will require re-proof.

so, now then the question becomes what is adequate barrel wall thickness at end of chamber for damascus and twist steel barrels?

Min Walls are .036 in both and chambers are 2 5/8. No reproof marks. It is strange that export was permitted as my understanding of the rules of proof is that in order to be exported from Europe, every gun must be "in proof".

Why do you think it was not honed out once in the USA?
Also, many rules were broken in years past (and may still be!).
It was only once the proof authorities started prosecuting exporters who were flouting the rules, mainly on information supplied from the importers I believe, that people started taking the export proof rules seriously.

owen: what is wall thickness in front of chambers?

Thanks everyone for the information!

Toby, Gun came from Kirby, I will ask him if he honed it or had knowledge of honing. He stated that it was freshly imported from his �continental source�, thus my perhaps incorrect assumption of an out of proof import. Ed, walls are .150 just ahead of chambers. RTW, sorry to hijack your thread!

.150 in front of chambers and .036 minimum wall thickness sounds good to me...could be ok for bp loads?

however, with .779 bores, its gonna be tough getting a good wad seal...unless gun is chambered for 10 ga shells...