If you have trouble finding #10 caps you can change the nipple to fit #11 caps. 3f powder is what you want to use but 2f would work if that's all you can find.
Also in a pinch(no pun intended)you can pinch the number 11 cap to make it fit tighter.
I would use 2F in those old pistols or any other old firearm. Keep the pressure down. 3F has higher numbers than 2F for pressure. I wouldn't want to stress that old steel overly much.