It's difficult to pay much heed to P.O. Ackley's velocities. IIRC, some of the loads in his books weren't even chronographed, velocities being estimated from trajectory.
Some other loads weren't even from his own tests, but from other guys who provided him with info. God knows how these sources came up with their velocities. Pulling in ballistic data from less than reputable sources reminds of the fellow who once told me "I know my 204 is shooting 4000 fps with 39 grain bullets, because it's louder than factory ammo".
