If your rile is the Browning Traditional Hunter Single-Shot, I'd keep it. It's bound to increase in value simply because the chambering is unsual.
If it is the Rossi "Puma" copy of the Winchester M1892 lever action design, I dunno. that is too new to evaluate yet.
Speaking strictly of calibers, that .454 can shoot full-charge magnums, or the .45 Colt for milder recoil and target impact effect.
The .45-70 is one of the easiest cartridges to load for and versitile to boot. A classic brush buster and old-West aura too!
As for the Marlin 1895 series .45-70 rifles, I LOVE them. Great shooters, balance, and plenty of old west looks and feel. If you plan to shoot lead bullets, or you handload for that .45-70, I'd certainly get the ones with Ballard-style cut rifling, not the Micro-Groove barrels.
I hate to answer your question with a question; but I gotta ask, what would you be using the rifle for? Big game hunting, plinking, etc? That would be my motivation towards returning/exchanging the .454 Lever Action. I've heard nothing but good comments (so far) about these LSI Puma .454's since they hit the market. Might be a question of what you really need more, a short & handy, very powerful for a pistol caliber .454 carbine or a short & handy .45-70 that can cover the whole range of power.
Just my 2 cents. I'm sure either one will serve you well.
The 454 out of a rilfe should duplicate some of the velocities of the 45/70 with a bit lighter bullet. In most (but not all) hunting situations the 45/70 is a lot more power than you will need and the 454 can use lighter 45 Colt loads as well. If you are in a situation where you need the massive bullet weight and power of the 45/70 (i.e. Brown bear back-up) go ahead and switch, but IMHO the 454 would be a lighter and more versatile package for 90 to 95% of most typical hunting and shooting needs.
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