Regarding that site's claim on 6.5x55 American ammo having true velocities from 22 to 24” barrels for Winchester, Federal and PMC 140 grain loads and run between 2400fps and 2450fps. . . . .
Winchester gets 2550 fps from their factory loaded ammo with 140-gr. bullets. Most folks' factory rifles have bigger bore and groove diameters than what Winchester used to clock that load. So, naturally, they'll have lower muzzle velocities. Such is life with all factory ammo in factory sporting rifles.
Norma's 156-gr. load leaves at 2559 fps in their test barrel.
SAAMI's spec for pressure is 46,000 CUP which converts to about 53,000 PSI. The site states Military 6.5x55 ammunition was loaded to a pressure of 3200 ATM which converts to 47008 psi.
Last edited by Bart B.; December 2, 2012 at 07:57 AM.