Actually with a 1-72 twist (what a nice twist) I think your best accuracy will always be a roundball. The nice thing is with that slow twist, you can push the roundball a lot harder in most cases. I shoot a .58 caliber with a 1-70 twist and have pushed that to 120 grains of Goex 2f with still, excellent accuracy. My hunting load is only 100 -110 grains of Goex and that 284 gr roundball. Very little will walk away from that I am going to guess.

If I were real concerned with shooting a conical, I simply get a barrel that was made to shoot them. I did not notice if you mentioned the make of your rifle, but there might be other barrels out there, much better suited. From the rate of twist, I would almost guess something custom. I'd just shoot roundball and lot of them. Then get a different rifle for your conical playing...