Had a similar problem on a 1909 CE.
Attacked problem from a different angle. Closed gun with no shells or snap caps and measured face off--less than 0.001 inch.
Closed gun with snap caps (machined brass that caused no face off change in my A grade Fox)--face off was greater than 0.010 inch.
Closed gun with unfired factory high base bismuth and face off was greater than 0.008 inch.
Repeated with unfired Remington Club shell and face off was greater than 0.004 inch.
I then measured the rim depth on the A Fox and a 12 guage Model 12 duck gun and they were approximately 0.012 deeper than the CE grade Fox.
Took the gun to my gunsmith and he confirmed my measurement and
deepened the rims the appropriate amount and the "problem" went away.
FOX SXS
