Chris,
Depending upon how you get decent results on target and regulation I’d opt for cast bullets.
No worry about where to find “in stock” jacketed bullets, no compromise on best bullet diameters to fit the bore/groove, no cleaning copper fouling…..
Any bullet mix from 20:1, 15:1, wheel weights, or Lyman #2 should work just fine at about 1650’/sec for expected double rifle accuracy and distances. I’d personally use a gas check bullet, but that’s just my preference. A card wad at the olain base bullet base would work about as well.
- Mike