Hey Dave, not sure about the powder being used. The guys here helped me out using 16 grs of 2400 powder. Also, my lead bullet has a long nose .301+ and .311 sized. But my bore is bigger. You should be good with the size your shooting. And is the muzzle good? I/m using Lymans bullet lube for my 311334 Lyman bullet. 183gr? about. I can shoot 2.5" @100yds with mine. Hang in there, there's a sweet spot somewhere for your rifle.
Another powder that has worked good is IMR 4350,
31-35grs seems to be really decent for cast bullets.
Also start checking the groups with a dirty bore. I've found starting out clean doesn't do good till the rifle has fired about 5 rds, then the groups start tightning up.
Hope this helps alittle! I love shooting cast in my rilfle.
TerryR