Both my super 14 and my 23 inch carbine barrels shoot 45-70 cast bullets well, Not nearly as good as my 12 pound rolling block, but pretty good for a very light set up. Never had any issues with 45-70 throat....now 30-30 is a whole nother deal. All 3 of the 30-30 barrels I've had over time required the use of a throating reamer to make them shoot. brass, reloading dies, bullets, etc are all much easier to get in 45-70 than 38-55, but the 45-70 will kick more. If you stick to reasonable loads in the carbine, it isn't too bad, the super 14 beats you to death no matter what you shoot out of it.
regards,
graycg