I agree you may only have a lube problem, not a powder problem.
If you are going to use such light loads, AND you have a shoulder problem, you may also have a gauge problem. The 10 bore was meant to throw 1.5 ounces of shot or a 650 grain (rough guesstimate) ball. So you have that weight pushing back on your shoulder as it moves forward. Dropping the powder load to 2 drams as you are doing really drops the muzzle velocity of the shot, and so defeats the purpose of the gauge, which is for waterfowl. Ducks and geese really have good protection with all them feathers, and if you don't have good velocity, you won't penetrate, but merely wound, if you do any damage at all. OR..., you have to get them in so close..., that a 12 or even a twenty gauge with the same powder and 1 oz or even 7/8 of an ounce of shot would be more effective.
IF you're not going for waterfowl, then I'd suggest a 20 gauge, with 55 grains of 2Fg, and 3/4 ounce of 7.5 shot. That's a nice, moderate load, that will slay any upland fowl, as well as squirrels and bunnies, while not beating up on your shoulder.
LD