With the greatest respect to the OP, this "rainbow trajectory" stuff is a red herring. The 45-70 comes from a different era in firearms technology and was designed for a propellant that required substantial case volume to propel large bore bullets of 400 - 550 grs at deadly velocities. Large bore, heavy weight bullets do not require the terminal velocity of smaller bore, lower weight bullets to achieve the desired results:
"The firing was done by Mr. R.T Hare of Springfield Armory who has the enviable distinction, so far as is known, of being the only person in the world who has hit the 'Bull's-Eye' six feet in diameter at 2,500 yards with three different rifles, and who has ever fired at and hit so small a target as that described in this report at 3,200 yards.
In comparison with this, all other so-called 'long range firing' pales into insignificance. The gun was held under the arm, a muzzle rest only being used" - From
The Report of the Secretary of War, 1880, Volume III, under the chapter titled, "Extreme Ranges of Military Small Arms," and describing the Sandy Hook Trials of 1879 and the results for the 45-70 from Trap Door rifles.
http://www.freerepublic.com/focus/news/843705/posts
Small bore bullets require high terminal velocity to transfer the levels of energy required for effective use. In doing so, they deliver a flatter trajectory and less recoil. That is all quite good and a reason that we like zippy, small bores. But there remains something to be said for displacement and while there clearly is a substitute for cubic inches, it may not always be a good one.
The 416 Rigby, 458 Winchester, 404 Jeffery and other fabled large bore dangerous game cartridges deliver heavy weight with relatively flat trajectory, albeit generally in use at 100 yards or less. They do so at the cost of very considerable recoil.
While the OP writes of the 45-70 delivering heavy recoil 1) that's relative - the above mentioned big bores offer substantially more recoil 2) that depends on the weight of the rifle - in an 18" Marlin Guide Gun, a very handy rifle, it will do. In a 10 lbs rolling block, not so much. Use black powder rather than smokeless, and the recoil becomes a hard push rather than the snap of smokeless.
The 45-70 propels enough bullet to shoot through any game native to North America at any reasonable distance. It was responsible for the near extinction of the bison. It does so with less recoil than both the larger dangerous game cartridges and smaller bore, flatter trajectory cartridges such as the 375 H&H, 350 Magnum, 300 Win Mag, let alone the Weatherby Magna. There are instances where less recoil will allow some shooters to be more accurate. The 45-70 can also be had in rifles that cost considerably less than those built for these magnum rounds. A Marlin 1895 can be had new in the $650 - 700 range. Even fairly tatty used 375 H&H bolt guns will be hard to find at that price.
But, the rainbow. Physics tells us that every cartridge begins to drop below the plane of the muzzle shortly after departing said muzzle. So the rainbow is entirely relative. Man up and learn to shoot, and the 45-70 presents no particular challenge. One learns fairly quickly what the drop is at various ranges and therefore, where one's hold needs to be. The hundreds of folks that shoot 45-70 at the Quigley every year out to 800 yards and beyond will be quite surprised to learn that they cannot do so.
Horses for courses. The 45-70 is not a great round for prairie dog shooting. I predict that it never will be. It was very good at killing very large bison. It still is. Since its debut in the last quarter of the 19th Century, a lot has happened in firearms and cartridge technology and we have a lot more options available. The 45-70 remains very good at killing medium to large game at short to medium distances and very interesting to use at quite long distances. And, there's an important element of nostalgia. And there are very odd folks like me that still like to pack them full of black powder and try to hit targets rather far away with big hunks of lead. That's why it's still around.
