Commercial ammo manufacturers can load a mix of powders to get specific performance not available to the average handloader without the sophisticated pressure and burn testing equipment they have. For example, with a std max load of 16.7grns load of H110 and a Zero JSP 158grn bullet, at 6,100ft on an 84° day, I was only able to squeeze out 1,8227fps out of my 24" Rossi rifle and 1,7891fps from my 20" Rossi carbine and with a 'Elmer Keith' level powder load of H110, I could only manage 1,977fps and 1,941fps respectively. That's well below the 2,153fps they claim they got with they 158grn 357mag Heavy in a shorter 18" Marlin.
Note that my loads produced higher velocities in the longer barreled rifle with both magnum loads. I don't know if Buffalo Bore's ammo would produce higher or lower velocities in the longer, 24" barrel as they may have optimized it for the shorter carbine length.