Barrel Wall Thickness

[Bill Murphy]

I have a Parker that was pitted when I got it and it doesn't seem to be pitted now and I never did anything to it except scrub and shoot it for many years. I also bought a "ruined" A Grade Fox 16 gauge several years ago. After a very agressive scrubbing session, the barrels were as new. I think some "minor pitting" is really surface rust. It isn't rocket science to mic the inside of the bores and compare the measurement to the known standard. Some exceptions to the Parker standards were on the big side, but I think we know what is unreasonable and indicates a hone job.

[VH20]

Bill,
Are you using your discarded sheets of old sandpaper to make shot-column wraps for your reloads? ;-)

[Bill Murphy]

That would be the easy way.

[Tom Brown]

Would anyone know what the wall thickness would or should be at the muzzle for say imp. cyl, mod, imp. mod, full on a 0 frame 20 gauge Parker? Thanks in advance. T.

[Austin W Hogan]

Adding the numbers on Dr Drew and Robin's sketches give a breech width of 1.205 inches. Two 1.205 diameter barrels would be 2.410 inches; a two frame is 2.375 across the standing breech and most Parker barrels look like sewer pipe when compared to an English gun.

Best, Austin

[Dean Romig]

Originally Posted by Austin W Hogan

and the chamber wall thickness of most Parker barrels look like sewer pipe when compared to an English gun.

Best, Austin

Sorry Austin - I thought your statement needed a little editing

[Austin W Hogan]

I just took the micrometer to the chamber wall of a 1 1/2 frame DH which is a little under 7 pounds. It measured .190 inches. There must be a lot of lightening holes in those 6 and 6 1/2 pound English twelves if they have a .287 thickness. I think the diagram is in error; adding .080 for the difference in bore diameter and chamber diameter makes it a little closer, but not quite as thick.
A three frame ten is .245 at the breech.

Best, Austin

Added; Bill is correct, a flat or dovetail is cut to join the barrels at the breech removing about 1/8 inch from the breech width.
I just measured a three frame 12 ga barrel. The chamber wall is .265 inch thick. The barrels are stamped 5 12

[Bill Murphy]

Austin is right and the diagram is wrong, at least for a breechloader. No English bird gun has .238 chamber walls. A second thing to consider is that the barrel wall thickness at the chamber is not doubled at the inside in most double guns. Austin's .190 chamber wall dimension is way less than .380 between the chambers of a 1 1/2 frame Parker. The one I just measured is only about .308.

[Jean-Paul Lavalleye]

Here are some minimal chamber wall thickness, at forcing cone end of chamber, I've measured for shotguns either in proof (bore diameter in proof 9" from the breach) or (for a very few of those listed below) so deemed by Kirk Merrington. All also have min wall thicknesses of ≥ 0.020, preferably ≥ 0.025.

English:
James Purdey (1898) 12b., 2.5" chambers: ≥ 0.100.
James Woodward (1909) 12b., 2.5" chambers: ≥ 0.098
James Woodward (1909) 12b., 2.5" chambers: ≥ 0.103
Boss (1897-8) 12b., 2.5" chambers: ≥ 0.090
Westley Richards 12b., 2.5" chambers: ≥ 0.090
James MacNaughton (1895) 12b., 2.5" chambers: ≥ 0.095
Wm. Pape (1898) 12b., 2.75" chambers: ≥ 0.100
EM Reilly (1887-1904) 12b., 2.5" chambers: ≥ 0.091
Henri Egg (1870) 12b., 2.5" chambers: ≥ 0.108
WH Monks (1875-87) 12b., 2.5" chambers: ≥ 0.116
WC Scott (1905-6) 16b., 2.75" chambers: ≥ 0.105
Francotte (1938) 12b., 2 5/8" chambers: ≥ 0.098
Westley Richards (1905) 20b., 2.5" chambers: ≥ 0.098
WW Greener (1922) 20b., 2.75" chambers: ≥ 0.098

Belgian:
Francotte (1894-5) 12b., 2.5" chambers: ≥ 0.085
Francotte (1896) 12b., 2.5" chambers: ≥ 0.085
Francotte (1930) 20b., 2.5" chambers: ≥ 0.095

French:
Verney Carron (1950s) 12b., 2 5/8" chambers: ≥ 0.100

German:
Wilhelm Brenneke (1902) 12b., 2.5" chambers: ≥ 0.110

If we are concerned about shooting safe vintage guns, shouldn't we be concerned about the thickness of the metal where the chamber meets the forcing cone, where the pressure is higher than further down the barrel (where we look for ≥ 0.020") and how low (thin) can we go? Looking at the data above, is a 16b. with a chamber wall that is 0.076"-thick at the forcing cone OK (even though the barrel wall min thickness is 0.030") safe to shoot? The answer to this question seems to be "yes" as this Parker had clearly been shot quite a bit and still has factory specs. Is there actual data somewhere on this point?