I have never reloaded for the 340 W but had a Ruger #1-B rechambered for the 340 W that my grandfather had given me. I only fired Federal 225gr Trophy Bonded Bear Claw factory bullets in it. I always got less than one 1" groups @ 100 yards with this load which really wasn't very fast @ 2950fps.
Cam

rojo ----- My .340 Wby likes 240 grain North Fork bullets best, next is the 225 grain Swift A-Frame then 225 grain Barnes XLC. RL-19 is my powder of choice with Fed 215M primers. Every barrel is an individual, you simply have to shoot yours enough for it to tell you what it likes. The last thing you want to do is pick a bullet and shoot only that bullet, then if it doesn't shoot it well conclude the rifle is no good. Good luck and good shooting.