As Gunman says, 1 1/4 oz of shot.
However the acceptable shot load is only relevant to CIP cartridges. In some Mega-High, LongBrass, FarKiller cartridge with 1 1/4 oz load, the pressures may be much too high so please select your ammunition with care.
This is the joy of living in a CIP regulated environment: if it says 2 3/4" on the box you are good to go!
Also one should bear in mind that what the gun was reproofed for is not necessarily what the ancient wood and black powder designed action will take happily over multiple shots. The odd shot may be fine but the pounding provided by a round of clays may do real damage.
