With the wads available back at the time your family Parker Bros. was made, the recommendation for these guns was to use over-size wads -- 9-gauge wads in 10-gauge guns and 11-gauge wads in 12-gauge guns. Note the loads No. 56 and 57 for Parker Bros. guns in this 1886-7 Chamberlin Cartridge Co. catalog --
1886-7 page 6.jpg
1886-7 page 7.jpg
These old Parker Bros. guns with their over-size bores have been used for the last hundred and twenty years or so with regular wads. Over-bore barrels have been in and out of fashion throughout the history of cartridge shotguns. Today we have a number of trap shooters banging away with Stan Baker "Big-Bore" barrels with .800-inch bores all the way to the choke?!?