If you know (or can find out) the pressure of those loads, and if they are low pressure shells designed along the lines of the PolyWad Vintagers and similar loads (7,000 psi +-) they should be o.k. I understand when the Fox guns were originally built it was routine to chamber shotguns a tad short, had to do with the old felt and card wads, I believe. As such, the extra 1/8" should not be a major factor IF the pressure level of the shell is acceptable.