I sold a Parker Hale - or maybe it was called "Inland" .264 Mag. English made Mauser to a fellow back in 1976 from the gun shop I worked at for a shot period of time. I started loading for him as factory ammo blew the primers right out of the case, expanding the pockets so we ended up sending it back to the distributor as well. It blew primers with anything over the starting loads in the Lyman #45 manual. I don't know what the velocities were - but it was downright scary with the factory 140gr. the fellow bought. We got a refund and he bought a Winchester m70A .243 for the little Island deer.
The one I had worked just fine, although was a bit slow - only 50fps faster than my .260 CLC, but used 33gr. more powder to do it. 'Course, the CLC had a 26" bl. and the .264 mag. was Winchester's fast 22"er.
In a 26" or 28" bl. it would be a great mountain rifle.