While H4831SC and RL-22 sure work in most 6.5x55's with 140's, since I did the update of "Loads That Work" I've tried Ramshot Magnum, a powder Marlin1895 mentioned as a possible.
Magnum is a very slow-burning ball powder, so fits well in cases where powder space might be little tight. Ramshot lists maximum loads from 49.8 to 51.6 grains with 3 different 140-grain bullets for muzzle velocities between 2712 and 2778 fps from a 24" barrel--at around 55,000 psi, as Marlin1895 mentioned.
I load 50 grains with the 140-grain Nosler Partition in my custom FN Mauser with a 21" Lilja barrel. It groups 3 shots into 3/4" or less at 100 yards at just under 2700 fps, even from the relatively short barrel.
