Looks good. You'll have to give a range report.
Today I set off to the range with my 50 & 58 and possibles in hand.
I started off with 100gr charge of Goex 2F 0.015 Oxo lubed patch and wasps nest at 50 yards. The rb hit low so adjusted the rear sight 8 clicks up, fired another, still low so I doubled it, 16 clicks up. Still low so I went to a 110gr charge. Recoil was near nil, I actually think my .54 kicked more but of course not as heavy as this 58 bbl. So after the 110gr charge the rb's started hitting where I was aiming and slightly left.

After a few more shots I tried a shot ea. from both Hawken rifles at 100yds. I basically covered the green ring on the target with entire front sight and squeezed the trigger. I was quite impressed on both shots.
Then I went back to the 50yd and fired one from the kneeling and one standing.

I was able to recover a few of the round balls in the berm. An unfired rb weighs 287.0grs. The recovered rb's ranged from; 286.7grs, 284.2grs & 280grs.
When they hit the dirt they hit with some
"mighty authority"
I tried a new patch that my brother ordered from October Country called 'Daisy Ticking'. These were .010 and loaded with wasp nest but showed signs of burn thru so I went back to the .015 thou patch.

I had alot of fun with this 'beast' but had to cut my day short as the wind picked up and -2 was close to -10 and the air was damp. But there will be a next time

I intend on looking up what a max charge is for the G.M. barrel and give that whirl.
Cheers,