The AH in the box stamped on the left side of the breech indicates the rifle was made in 1981. It's in wonderful condition, especially considering the age!
Just looking at the grooves, that rifle looks like a round-baller to me. My old Gun Digest Black Powder Loading Manual (1983 edition) by Sam Fadala shows a .54 caliber "Armsport Tryon Trailblazer" rifle which is a dead ringer for that one (except for the dyed triangles). Mr. Fadala listed a twist rate of 1:63", with grooves .015" deep. If the subject rifle here is in fact one of these, it is definitely intended for patched round balls.
Mr. Fadala tested his rifle with up to 120 grains of FFg, which he recommended as a maximum load. Interestingly, at 100 yards, he thought there was not a significant difference in energy between the 100 grain and 120 grain loads, and he recommended 90 grains of FFg as the optimum load. However, he tested loads with as little as 40 grains of FFFg. This is evidently a very tolerant rifle, with regard to powder charges. All of his testing was done with .530"/225 grain round balls and .010" patches. He did not test Minie or Maxi bullets, stating "...we felt the 1:63 twist was best suited to the round ball."
NOTE: I was thinking the information above might be helpful, but moderators are welcome to delete my post if it is considered inappropriate for this sale ad.
Best of luck to all concerned!
Notchy Bob