What is that bullet's exact length, what FPS are you at, and what is your twist rate ??.....
Loads that work with a Proof barrel means nothing without knowing how much throat
is available and how much your jumping that bullet. Did you find the jam point to start ??
For 1.5" groups, it can very well be something else. What shape are the groups generally ??
Any reason you chose the Nosler's ??
Bookmarks