A single layer of white teflon tape will tighten the bullet enough to keep it on the charge without affecting accuracy. The barrel should be clean and dry of oil.
This what I do with my White Bison. The teflon tape mimics shooting with a fouled bore which is what Doc White suggest.
The tape can be skipped on the second or subsequent shots as the barrel becomes fouled with powder residue. All shots should end up withe the same POI.