I had one on a .45-70 as well, though mine was a Marlin 1895. I also had several hundred rounds of STOUT loads through the gun and never had a single problem.
If I had a Ranch Rifle instead of a standard Mini, I'd have kept the scope when I sold the Marlin, but alas, no easy, solid mounts for the older Mini's.
The only thing, don't expect the light gathering capabilties of a 50mm scope with this thing. It's a great little scope, and if you've read the reviews on the Midway site, I think a lot of people agree, it's just not built for precision shooting at long ranges in low light.
That said, if you take a 20mm lens, divide by 3 power, you still have an exit pupil of 6-7 mm, this is about as big as the pupil of your eye is going to get, even in low light, so even discounting some light loss through the lens, you've still got just about as much light as your eye can handle, even at the highest power.