Fox Collectors

I have a 20ga Fox Sterlingworth Utica in excellent condition shipped in 1936 with a 1933 serial number. Apparently the barrels were bored out Cyl and IC. The letter says M and F. I had the chambers measured and they are 2 3/4. Can I shoot higher power shells in this gun than the RST I have been shooting? Or should I stay with the lower powered 1100psi shells?

While no one can tell you over the internet what loads may or may not be safe or appropriate in a given gun, the 2 3/4 inch 20-gauge, progressive burning powder, high velocity, 1 ounce loads, like the Western Cartridge Co.'s Super-X, had been on the market for well over a decade when your gun was made. Most of my 20-gauges have digested some Super-X type cartridges when I believed the situation called for it. One needs to apply some "common sense" to these kinds of things. I briefly had a little Fox 20-gauge, that must have been pretty close to the minimum weight they made, and it got limited to 3/4 ounce 2 1/2 inch Lyalvale cartridges.

I am not interested in shooting high powered shells probably would go no higher than 1200psi on the box.

Your Fox was built strong and undoubtedly can handle modern ammunition which is loaded to a SAMMI max pressure of 11,500 psi, however, recoil is of greater concern due to the 75 year old wood. To be on the safe side I would limit my choice of ammunition to 7/8th ounce loads at 1150 fps and chamber pressure in the 9,500 psi range to stay below a recoil force of 15 ft lbs.