Found a couple more 10g in my files measured by a friend; both 3 frame pattern welded Parkers and both with bores .794"
#1 end of chamber .140"; 9" from breech .093" and 9" from muzzle .050"
#2 .114"; .059" and .040"

All the below had standard bores and chamber length and were felt to be unaltered

End-of-chamber:
3 No. 1 1/2 frame 12g fluid steel Parkers were .088", .092" and .105"

4 No. 1 frame 16g fluid steel Parkers were .084", .100", .105" and .111"

No. 0 frame 16g fluid steel Parker .104" L and .099" R

A No. 0 frame 20g fluid steel Parker was .091"


http://parkerguns.org/forums/showthread.php?t=31521
12 gauges
Baker Paragon L-.97, R-.103 2 5/8" chamber
Win 21 L-.115, R-.119 2 3/4" chamber
LC Smith Field L .102, R .105 2 3/4" chamber
Parker PH L .107 R .115 2 1/2" chamber, 1 frame
Parker VH L .90, R .90 2 5/8" chamber, 1 1/2 frame

More numbers
https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=379803&page=3

http://parkerguns.org/forums/showthread.php?t=1565&page=4

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


Wall thickness recommendations are dependent on the tensile strength of the barrel steel and pressure of the load for which the gun was designed

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