54Bucks - I currently have 2 .58's and love them both- a 24" Musketoon and a double barreled Kodiak that I re-modeled a bit - it regulates perfectly. The guys here can attest to it's accuracy on the bush trail walk we shoot and have on numberous occasions, right here. I've never had a .54, but also had 4 other .58's in the past. I love the calibre - it is perhaps to a .50, as the .58 is to the .54. The .58 is a big step form the .50 and the .54 is in the middle.
A flat butt and the .58, given 9 1/2 pounds, is quite plesant to shoot for a powerful gun, although few (no one) wants to shoot my double rifle, even with it's flat butt. They say it appears to kick a bit - or perhaps more than that. It's short barrels certainly bark. I shoot 100 or 110gr. in it for it's regulation loads, along with a .574" ball and .0225" patch. It also lieks a .020" striped ticking patch.
The E. Marshal is a perfect platform, as-is an English Sporting rifle, if heavy enough. If of short barrel, the English gun would need a straight barrel I think, or perhaps single taper, not a heavily swamped lightweight barrel as are the short 28" to 31" comercial bls.
This rifle kicks, is of English design, but is easy to shoot due to it's weight of 9 1/2 pounds. Here, a mere 140gr.of 2f being touched off. It's the 200yard accuracy load. Less powder is less accurate.
This is a .62 Hawken in full throw - Taylor shooting, back in about 1977, I'd guess. He didn't use light loads- probably about 120gr. here.