I have only tested a few barrels, 20" wsa a little disappointing, 26" works well, I will be trying a long one in the future.
The 30 cal will go faster than the 284 in the same case with the same weight projectile.
Its terminal performance should be better short-medium (normal hunting) range, its BC will be less, assuming same type of projectile.
I will have a Rem 700 280ai shortly so will have a better idea of comparative performance.
Bookmarks