the Big Horn gun is not cheap, and its not a .45-70. The action is kind of an improved, stretched 92 but isn't quite long enough for the .45-70 round. Its a quality build, listed as a production gun but its more like a semi custom item, with a price tag to match.
Discussions of "strength" of rifles always amuses me. Even going back to the P.O. Ackley blow up tests. Other than as a point of academic interest, they are of no practical value. unless, of course, you're planning to blow up a rifle on purpose.
the operating tolerance and the failure strength of a firearm are two separate and different things.
I've got close to half a century's personal, hands on experience with a number of .45-70s, single shots, levers and even bolt actions. Old Trapdoors to modern Rugers, and my experience is, that as loads go up, cases will stick (at which point the smart people STOP! and back off a bit) before they rupture and cases will rupture before the action fails.
Doesn't matter to the shooter if the action fails at 90Kpsi or 117 or 134, what matters is the working pressure limits of the various designs and operating BELOW that.