Heelerau

I have a 62 that has Forsyth style rifling in a 104 twist.

The bore is .623 and I shoot a .620 RB.

It likes a tight load.

New barrel and I have only tried 135 and 150FF.

My tapered paper cartridges and a .610 RB shoot same point of impact.

You may want to try a .715 RB, or what ever is .005 smaller than the bore.