Chasseur, I have a twin to your rifle so I was understandably impressed with how yours shoots.
I noticed that you are using a Ranier 335gr bullet.
I looked at their site and it seems that they are .500" diameter. Is your bore .500" and do you and Curl think that the bullet is bumping up to fill the grooves?
I thought smokeless loads didn't work in trying to bump up soft bullets but whatever you are doing seems to be working quite well!