My compliments to Breck - that is the barrel evaluation our guns (eyes & fingers) deserve.
I believe however Breck's "end of chamber" wall thickness of .162" for a No. 1 frame 12g must be the BREECH end of chamber.
The muzzle end of chamber (immediately prior to forcing cone) is of more importance, with the MWT for usually > .105". Factory small bores may be as low at .090".
Because the angle of the cone exceeds the external taper of (most) barrels, the forcing cone MWT is usually the same or slightly greater than the end of chamber, and .110" would be typical.
Lots of numbers are here
http://parkerguns.org/forums/showthread.php?t=31791
and
http://www.doublegunshop.com/forums/...=379803&page=3
Threaded Mode