2 or 3 thousandths of an inch is pretty tiny.....

.016 .... not that tiny...

The variation left vs. right?

Thank you Edgar. It appears the pin is measuring the forcing cone wall thickness? Could you please post the end of the chamber measurements?

It has been my experience that the thickness at the forcing cone frequently exceeds that of the end of the chamber. The angle of the forcing cone is more acute than the external taper of the barrel; as illustrated

http://pic20.picturetrail.com:80/VOL.../411834258.jpg

This may not apply to small gauge and continental game guns, and does NOT apply to guns with chambers lengthened.

And so we all don't have to go looking. End of the chamber measurements.

http://parkerguns.org/forums/showthr...096#post158096

http://parkerguns.org/forums/showthr...?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

Would it be safe to say the weakest point in the illustration is the beginning of the forcing cone ???

And by legnthening the chamber you would change the angle of the forcing cone..

A better question is what is the safe wall thickness where the pressure peaks?

All pressure - distance curves

http://pic20.picturetrail.com:80/VOL.../410772139.jpg

http://pic20.picturetrail.com:80/VOL.../314583132.jpg

1 1/8 oz 1200 fps modern powders, recognizing that Unique is slightly modified "Infallible". Unique and Green Dot were equivalent.

http://pic20.picturetrail.com:80/VOL.../412289224.jpg

Yes and Yes to both questions and by lengthening the straight wall of the chamber deeper into the ever decreasing taper of the outside of the barrel you are negating the safe wall thickness of the barrel that the manufacturer had built into the gun when filing the barrels to the safe taper they were made with.





.

As Requested. I could get varying results are different points, but still at the same depth, however I took these at the same points as the previous two pictures. None were lower than these measurements.

What point are you making by showing those measurements? They seem pretty safe.