OK, strange maybe to want a rifle barrel for almost a single reason: I enjoy paper patching .451" pistol bullets intended for use in .45 Colts and loading them into .458 bores such as 45/70s, .458 Win Mag, and a custom .458 American [.458x2" before it was commercialized in almost same form as the .450 marlin.
Speer's factory swaged 250gr SWC lead bullet is a great plinker in a 45/70 when paper patched as are other "lighter than 300 grain bullets.
Got to wondering what you guys with 16" to 23" 45/70 CONTENDERS are shooting in yours. When not shooting PP bullets I bought 300 and 350 gr JHC bullets for deer. Also bought some Remington 405 JSPs a dozen years ago when Midway and other gun supply distributors were selling bulk Remington factory bullets so cheap.
I don't care to shoot very warm loads in the 45/70 in a single shot because of excessive recoil. I've also had a Handi Rifle in 45/70, and a 12.5" pistol barrel in Contender, but not a 'rifle barrel'.......yet.
What ya shootin' in yours? [yes, this could lead to my finding/buying a 23" factory 45/70 Contender barrel....been close a couple of times!] : )