I wouldn't make any ammo for it just yet, most H&R 45-70s are short throated so you won't be able to load them unless you seat the bullets deeper first, just a heads up. I'm a barrel-per-frame Handiholic so I don't add barrels usually, just more Handis!! But the BC frame uses the same SB2 frame, it's just case colored, so it can be fitted with any barrel they offer if your frame was made since 1999 except the 10ga and 12ga slug barrels.
I have two BCs, one is still a 45-70, I had the other rechambered to 45-120-3¼" Sharps Straight a few years ago, it's a hoot to shoot, and the shock and awe factor is priceless at the range!!
Both shoot excellent as do all H&R 45-70s, most shooters use trapdoor loads and stay away from the heavier low to mid 1895 level loads, particularly in the BC due to the unfriendly steel but plate, but even that can be remedied with a leather slip-on or lace-on pad and/or a little weight in the stock bolt hole.
I also have one of the all stainless 45-70 Ultra Hunters, it shoots the 300gr TSX-FB @ 2350fps into well under an inch at 100yds using Barnes Ruger data. One of my 22" 45-70s shoots the 300gr Nosler PP at 2425fps with the same accuracy. The other 22" 45-70 has a WGRS peep and a Firesight up front, it shoots the 350gr Hornady RN with 28gr of 2400 into less the 2" at 100yds with my old eyes, which is pretty good for me, dunno the velocity, but that load is favorite amoung the old timers here and works well on deer from what I've learned, but I've only killed paper with it!!
The 44mag and 45 Long Colt BC carbine barrels are good shooters, the 44mag has a checkered past due to oversize bores, but Marlin produced barrels made since early last year are good. The 45 Colt is also a good shooter, not to be confused with the 45/410 barrel which is kind of a novelty, but useful for many. I rechambered my 45 LC carbine barrel to 460S&W, still working on loads for it, but as a 45 Colt, it shot 250gr Speer GDHPs and SSTs at a little over 1900fps, accuracy was very acceptable at about 2" with a low power scope.
Get em all, just figure out which to get first!!
Tim