When I gave my answer to the poster's question, I was trying to think in my mind, "where is this going?" When he answered with his goals, the answer became a lot more obvious. What he's asking about is a rifle design that will allow him to shoot heavy loads - both ball size and powder, and in that case, LOP has little to do with it.
Bob has it right about rifle design, and so does Acer, and Greybeard hit on a very important aspect as well. A rifle with a comb line almost parallel to the bore, a butt plate with lots of width and fairly flat (lack of crescent), and a pitch that allows the rifle to recoil down and away from the face rather than one like a Tulle musket which forces the stock upward against the cheek bone upon firing. I have recorded some stock dimensions, over the years, of rifles that fell into this category, and will post a few if you wish. And these fit ME. Your face shape, length of neck, arm length, meatiness of your shoulder, and even how far apart your eyes are, will bake some differences.
