Hoppdoc: I'd guess that such a combination {540/1550/flat meplat} is rare enough that the jury is out as to how it would perform on heavy game under bad circumstances. I've read of some work being done in South Africa and elsewhere studying the effect of various ogive configurations on deep penetration, and the results were very interesting, indicating that relatively minor changes can produce significant differences in terminal performance. If it works on the "real heavies" maybe it'll help the .45-70 to some significant amount? Until a bunch of big stuff is shot with such a combination I'm not willing to say it won't work. Maybe somebody here has experience with a similar load and can comment?

I do not. The load I shoot in my .45-70 is a 402 grain cast hollowpoint running at 1640 fps. Not even near the performance of the .470, etc. But my load is a killer and the bullet acts something like a Nosler Partition, shedding the front hollowpoint, leaving the rear shank to penetrate deeply. I do not consider the .45-70 the equal of a .500 NE or even a .458 Winchester Magnum, but I do have a soft spot for the cartridge and my Marlin that shoots it. I have killed bear, deer, varmints and two range cattle with it. I'll tell you about one of latter:

Some years ago some range cattle broke out of a neighboring ranch and wandered onto the road that divides my place. A girl struck three of them in her car at night, totalling the car and killing one cow, sending one off {never to be seen or heard from again} and breaking the leg of another. The next day the rancher was called in from Lewiston {where the Speer bullets are made} and he and his hand saddled up their horses and came by to round up the wounded one and push it to their stock trailer. It went berserk, chased him and his hand from the cedar mill to my line, then, when they backed off after the Sheriff's Deputy arrived, chased the Deputy under his patrol car where he stayed till it moved off of its own accord.

I knew none of this as I was at my business in town 20 miles away. I received a telephone call from a neighbor who merely stated that the rancher didn't want the critter and I could come and put it in the freezer if I wanted to.

I drove home and met a friend, who had just arrived and was as ignorant as I was. he went to his pickup and offered his .38 to put the thing down with. I declined and told him I wanted to try a new .45-70 handload so I'd take mine. i'm glad I did. The rancher always had a sick and demented sense of humor.

We found the rancher who pointed out the critter and took my friend and drove off some distance away. This seemed odd but I didn't say anything about it. The cow was in the mill yard lying down and chewing its cud when I approached from behind. I figured I'd walk up and get one in at an angle from side-to-side so I could maybe recover the bullet.

When I got to about thirty yards away, the cow spotted me and exploded off the ground, spun around and with no more to-do, came for me like I was a catcher and she was a Roger Clemens fastball. Our mobile butcher is a friend of mine and he has probably faced more bovine charges than any professional hunter I can think of {a lot of people call the mobile butcher because they can't load the mean one...} and he told me to aim for a spot about two inches lower than a line stretched from eye-to-eye on charging beef cattle as they come with their noses pointed more or less straight out. That's what I did and when I broke the trigger that cow piled up like a sack of cement dropped off the delivery truck.

When my kids and me skinned the critter out we were careful to trace the bullet path. It entered the head right at the edge of the cartilage of the nose and angled back, passing through the head, shattering the base of the skull and many vertebrae in the neck and coming to rest after it had penetrated over 24 inches of bone and muscle.

The .45-70 is no "elephant gun", to be sure. But in a light 7 lb rifle with great handling and excellent sights, it kept my ass out of traction, and that I am grateful for. If Sam wants to hot-rod it and kill buffalo with it, all the power to him. If he finds out it doesn't work for him, i'm sure we'll hear about it in good time.