Hey Petamocto,
As I said, I bought a box of this stuff from Ammo Supply about a month ago. The muzzle velocity is listed by the factory at 1260 fps for the 305 gr. WFN gas-check hard cast lead bullet. But (for some reason) there is no mention of the barrel-length that produced that number. I couldn't find it on the factory website or anywhere else on the Internet, either.
So I just now picked up the phone and talked to a friendly/helpful fellow in HSM's technical department down in Montana ... and learned that them numbers are from from a six-inch barrel. Very impressive ... my Rossi Ranch Hand has a 12-inch barrel, so I am good-to-go.