The load is not marked anywhere on the rifle. I'm hoping that the "230" on the barrel flats is the bullet weight and that the "80" on the barrels is the powder weight.
No. These are standard pre-1887 Birmingham marks. Bore size was a required mark after 1855, and still is today. Until 1887, bore diameter was marked in gauge for both shotguns and rifles. This was stamped between the definitive proof mark and the view mark, as it is here. The "80" is unquestionably the bore diameter in gauge.
I don't know what the 230 on the flats is. During this period, while the maker might well engrave load data somewhere on the rifle, it was not stamped by the proof house. The absence of load data stamped on the flats or underside of the barrels on a rifle of this period is normal.
Bullet diameter seems to have run .403" to .408". I think I'd slug it again.