I just found my chronographed data for the .58 hawken I had. The barrel was 32" by 1 1/8" octagonal and Green River by make. The twist was 60". All velocities I've printed before were attempts to remember from 24 years ago and were low of what I actually got.
: 95gr. 2F C&H .575RB .020" Denim Bear Greased patch - 1,424fps.
:140gr. 2F C&H .575RB .020" Denim Spit 1,683fps
: " " " " " Bear grease 1,736fps
:160gr. " " " " Bear grease 1,867fps
:185gr. " " " " Bear grease 1,951fps
: The 140gr. charge became my favourite for a hunting charge due to it's exceptional acuracy out to 150yds.
: Although these sound high,
: Note - velocity vs pressure.
: Guns from .45 up show similar pressure with round balls for similar velocity. Therefore, the pressure of the top load I was using must have been less than 12,000 CUP, well within the strength of the rifle used & is in the range of maximum loads for Italian and Spanish rifles.
: GreenRiver Rifle Works lists working loads for their barrels as 140gr.2FC&H suggested load and 195gr.2FC&H as being maximum.
: This is considerably less than the 29,000PSI achieved with 100gr. RS Pyrodex with a 250gr. Sabot in a .50 cal muzzleloading rifle.