for an easy start, why not simply use the same bullet you use for the 30/30. Velocities you load won't differ much either. Heat treat if necessary.
One comment on the Ranch Dog designs... You're not likely to forget the sound of the first impact you hear. That huge meplat simply b-slaps whatever it hits. It's my go-to design when I'm serious about a kill.
I use any of my 160-180 grain slugs in the Savage .308 or '93 mausers and they shoot 'em all fine.