Lee 340 RNFP 457 Loads?

[Patrick Henry Brown]

Anyone here have any experience using the Lee 340 gr. 457 RNFP bullet in 45-70 with BP or Subs. I have an IAB carbine in 45-70 and thought I'd try this mold. Hoping to drop the felt recoil a little by using this instead of the 405 gr. HB. Figure to stick with 55 grains or so of 777 or FFG. Anyone have any feedback or suggestions?