Savorino,
I would not hunt deer sized animals with the Old army and round balls. Although many have with success. I think what you are hearing about lack of accuracy with conicals is from people that simply have not found the right conical or gave up after the first try. I use the Lee R.E.A.L. 200 grain bullet that was originally designed for .45 caliber muzzle loading rifles. The bullet seats easily in the chambers due to its driving bands that start small enough in diameter at the base to enter the chamber squarely. The bands graduate in diameter towards the nose. The bullet also has generous lube grooves. I have 4 Old Armys that have ajustable sights and they ALL shoot this bullet with a slight accuracy edge over round balls. I also burn a lot of 777 in them. It produces more velocity than black or Pyrodex. Also this powder seems produce a higher velocity deveation than black. The velocity deveation(at least in my testing) is higher with round balls than with the heavier conicals. If you want an Old Army with a bit more power David Clements can bore your cylinder's chambers to thier full diameter a bit deeper and get you a bit more velocity. This is a very modestly priced option. If you want an Old Army that would be more suited to deer hunting he offers a .50 Caliber(actually .485) 5 shot conversion. I should have one of these in my hands in the next few days and will post a report and pictures here.
Good Hunting,
Billy