King;
I don't have a Blackhawk in .30 Carbine at the present. but I used to use one for NRA Hunter's Pistol competition.
I used a 115 or 120 gr cast linotype bullet that worked very well, but I don't reckon that I still have the mold to find what the exact weight/shape it threw.
I won't give out reload spec [for liability reasons] but I reckon that the .310" 92 gr pill will be okay for plinking.
But you should check the chamber mouths to get the actual diameter. Mine were .308".
Please post what your results are.
MG