I agree with Capper. Choose a barrel made to shoot RB in a 1:48 ROT barrel. That means deep grooves.
I do not believe that RBs skip over rifling if its too shallow, or too fast a ROT. Using RBs in fast twist, shallow grooved barrels DOES require a tighter ball/patch combination. The patch and ball diameter insures that the compressed patch transfers the rotation of the rifling to the soft lead ball. Because you don't have the wide bearing surface of a bullet, when shooting RBs, you need to use a wider diameter ball- even bore diameter is not too much-- and a tight patch combination in barrels with a 1:32 ROT, and shallow grooves. Remember to put the coarse side of the fabric against your ball, and the smooth side against the bore.
However, if you do use a .495" or .500" diameter ball in your .50 caliber, and use a lubed, .015" thick patch, you should not have accuracy problems shooting RBs in that fast ROT.
Loading the ball into the barrel will require more effort, and you must clean the barrel between shots, so you don't stick a ball half way down the barrel.
But, A round ball can be "rotated" or Spun" at extremely high RPMs, and still fly straight. With black powder loads, you are not going to get enough velocity for the soft lead ball to shatter in the air, due to high speed rotation.
Since you want to shoot RBs to save money, and to plink, rather than hunt, there is No reason to overload the gun with heavy powder charges intended for long range shooting. 35-65 grains of 3Fg powder in that rifle will be more than sufficient for target shooting out to 100 yds. Most of your plinking will be at 25 yds, or so, where the lighter powder charge is all that is needed.
My brother once met a man shooting his .50 caliber hawken rifle at the range, and from the sound of his gun's report, the man was using very little powder. he was shooting off-hand at a 25 yd target. Pete talked to him, and the guy showed him where he had taped a 3 x 5 index card to his stock, indicating the powder charges to use for 25, 50, 75, and 100 yd. targets. Instead of changing his sight picture, this guy sighted his gun to hit dead on at 100 yds, and then reduced his powder charges for the shorter ranges, so that he could use the same sight PICTURE at all 4 distances. I think he as shooting something like 27 grains of 3Fg powder in that rifle to hit the center of the X ring at 25 yds. I don't recall what his 100 yd. powder charge was.
When asked by my brother WHY he was shooting such a light load, the man asked, " Just how much velocity do I need to push a ball through a sheet of paper?" I think its kind of hard to argue with that kind of LOGIC.
The same thing can be done with your rifle, and any chosen ROT rifling, or groove depth. I Don't personally see any need to shoot conicals for deer with that caliber, but you are entitled to your own views. My 1:48 rifle barrel from Green Mountain, has deep grooves for RBs, but I could also fire short conicals in it, using an OP wad to protect the base of the conicals, and seal the grooves from gas blow-by. :thumbsup:
I would rather use a gun with a .54, .58, or .62 caliber bore for hunting large deer( ELK, MOOSE, CARIBOU), with either a RB or conical, or for hunting Bears and wild boars that go over 200 lbs. For the latter dangerous game, I do recommend using conicals, because of the energy they deliver to stop these animals. Nothing is guaranteed, of course, and Every Kill depends on how accurately the shooter can place any projectile in a vital area. A miss with a .75 caliber bullet is still a MISS! :hmm: