I have shot double ball out of my .40, .45, and .50 cal. rifles, and have found the point of impact to be surprisingly close.
Recoil with the lighter caliber rifles was negligible. Impact on game is tremendous.
You "MUST" be certain that both balls are sitting tightly on the powder load. With tightly patched balls, that is no problem.
You will have to adjust for lower impact point with the two balls, but you are going to practice a little before hunting, are you not?
For practice, hang an old frying pan from a tree.
Shoot it with one ball, then shoot it with a double ball.
Come back and tell us the difference, especially your observation of impact on the frying pan.
Best regards
Fred