I just completed purchase of a 1984 Shikari (Model 155) in 45-70 Govt. It should be at my FFL next week and in my hands by next Friday....(thanks Jon for the 'tip'

!)...weird .....; to get what I wanted, I had to buy a rifle in CA that was made 60 miles from my home

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This rifle is described and appears to be "as new or new" so it just may be a great find; we'll see.
I shoot Black Powder and so I have wanted one of these to 'round' out my H&R BPCR selection so to speak. I have read that these rifles have "Ballard type rifling" and I believe a 1-20" twist rate, and I know that they are recommended for "Trapdoor Loads" only. So this is perfect for my use and a starget and hunting rifle with a 405 grain cast lead bullet.
My question is how does "Ballard type" rifling differ from "normal" H&R rifling? Also, as this is the same rifling used in the TC and BC and LC.....can it be assumed that these rifles were designed for cast bullet shooting? Any thoughts and or experience with this rifle is very much appreciated.