OK, folks go do some math.
Use ballistic software to compare a Sierra 30 caliber 190 HPMK leaving at 2550 fps (typical NRA match rifle use) against a Sierra 155 Palma HPMK going out at 3000 fps (typical Palma rifle use) then look at the wind drift difference at 1000 yards.
Use some high school trigonometry to figure out the rifling angle different twists present to bullets in different calibers. Most folks are really surprised to learn a 22 caliber 1:8 twist has the same rifling angle to its bullets as a 30 caliber 1:11 twist has to theirs.
Then compare the range of bore and groove dimensions to all the bullet diameters and you my well think there's a greater spread in peak pressure and velocity caused by this than small changes in the rifling's angle to the bullet. I think this is the most common cause.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master
Last edited by Bart B.; April 25, 2013 at 08:45 AM.