Stuart,Republic Metallic Cartridge has 10 GA 2 7/8" shells but are loaded with blackpowder, lead and bismuth. The Hogdon manual has reloading data for pyrodex with listed LUP pressure. This is one area, however, where reloading truly pays off, blackpowder shotgun shells. I can load for half price. My waterfowl bismuth load will cost 34 bucks for a box of 25. I paid 75 at Republic. I bought bismuth before Ballistic Products raised thier prices!
A facsimile of the 1908 Sears Catalog list two loads for 10 ga:
4.25 dram black/ 1 1/8th oz of lead shot
5 dram black / 1 1/4 oz lead shot
Set your powder measure to 115 grains for the 4.25 dram charge or 135 grains for the 5 dram charge. Your Pyrdex will still be the same volume as the blackpowder .
I loaded up some 5 dram 2f goex blackpowder, 1 1/8th oz shot "trap" loads and went 9 for 10 with my 10. When I shoot bp in my shotguns, I clean the same day so corrosiveness is not an issue. Lyman #2 Blackpowder Handbook and Manual has pressures going either way when it comes to Pyrodex vs. blackpowder. Sometimes pyrodex has lower pressures sometimes the black does.
Enjoy that 10!