No doubt.
I'd probably go the 4198, 3031, 4895 route rather than Trail Boss myself. Trail Boss is way early in the burn rate charts. Probably a bias passed on to me from family, but I tend to think of fast powders as hot powders as barrel eroders. Might be entirely false though. Trail Boss basically relies on that donut shape to achieve it's bulk goals. Interesting approach to be sure. But the do warn against crushing it up. Seems a big gimicky to me. But definitely works. No doubt about that.
BTW, the goal here is not "light loads" per se, though Trapdoor level loads are light by today's standards. The goal is to find a good load that is accurate, does the job, and is easy to assemble. That was the whole point of getting a 45-70... cast bullets are easier to make than jacketed, GC or paper patched. I want to keep the load process simple, the results good. The goal for this gun is for it to be my basic pick it up and go to the woods gun. Simplicity being a virtue here.
Well, when I get around to picking up the new Lee Loader, will be interesting to see what it's got for recommended loads as well.
Yes, with the possible exception of C.E. Harris' online articles I definitely plan to used "published on paper" loadings for the most part. I'm not real keen on having problems. But I would like to keep things as simple as possible.
I think you said you where a beginning loader. You should buy that Lyman Manuel and do some reading, leave the speculation to the arm chair quarter backs... 
4198 and 3031 are GOOD 45-70 powders BUT mostly used for heavy loads. 4198 CAN work for some med loadings, But heeping pressures under 28K or whats geberally considered ''trap door'' loads is where the powders I have suggested lie..
Choosing a powder form a bur rate chart is a recipe to BAD THINGS... Its a GUIDE ONLY!!
Barrel ''erroders''... 
Again brother, some reading from folks who know and don't speculate is better for everyone... 
Barrel errosion is a problem with HOT powders, but a bigger danger from errosion comes from hi speeds and hi PRESSURES. You are NOT into hi pressures OR Velocities with these 45-70 loadings. Now HEAT is a consern, as a rule of thumb if you cannot HOLD your hand on a barrel its TOO HOT TO SHOOT. It takes a good amount of shooting in rapid succession to get there...
Don't worry about the powders shape... Why would it be a consern? As long as you can meter it easily and accurately. (You can with Trail Boss) The large shape adds BULK, BULK increases VOLUME, this reduces risk of double charges as doubles likely don't fit!
Trap door loads are light loads, they go hand in hand. They are pleasant to shoot and if given the chance will work just as well!
ROGER THAT on fun loads!! Thats what we are ALL after!! If it wheren't fun, who would do it? My reason for my first comments was to make new shooters pause and look into the possibilities the use of some components can cause dangerious situations. Time spent reading thru a good manual will do new re-loaders more good that months of reading or listening to arm chair commandos...
Many of the guys here are accomplished loaders with many many years of experience. They use that experience when crafting some loads like these. Venturing into these waters with out that expertise can be treacherous. My reasons are simply to help, show the possibility of problems.
Good luck & SAFE re-loading,
CW
No, not exactly a beginner. But not a pro either. Just coming back to it after 15-20 year layoff. Trying to keep it simple mostly. Easy processes, easy to obtain or make parts. (Hence the cast bullet focus that led me to 45-70 from .30 cal. rifles.)
I picked up the barrel erosion story from my father. A long time gun fanatic from a long line of the same. Somewhere there are pix of the Marlin 189? shotgun his grandfather used that I was handed at one time. He seemed to have a massive bias against Bullseye in particular.
But he was precise enough he had his check weights redone on a scale at a jet factory down to about the 4th decimal place, LOL! So I'm sure he had a reason for that belief. But not sure what it was.
I've been trying to figure out if "fast powders" are by default, "hot powders". Actually I'd like to know more about how they engineer burn rates and such. What chemicals they blend, etc. What is left out in all the burn rate charts I've seen is an actual concrete burn rate, etc. I mean who's to say how far apart #7 and #8 are vrs. #9 and #10 and so on. It's a relative ranking and seems to leave a whole lot out.
Even a good reloading manual leaves that sort of info out. At least the one's I read as a young guy. It's like, there's nothing to hang you hat on when choose between two powders and loads with similar velocities other than perhaps pressure. So it's still guesswork to some degree... just guesswork within a framework of what's published.
Consider this thread, we've got opinions on both sides of the spectrum, and nothing to really prove anyone right or wrong for the most part. Sure, the really outlandish stuff may stick out, but everyone here has an opinion, and something they point at to back it up, and yet, there's not a complete concensus.
So for my technical side, there's a lot that one could try to deep dive into.
For my practical side, I'd just like to get it down to a few good loads that are easy to build and have latitude for variance. For example, black powder is often cited as being fairly forgiving of changes in charge weight, if but because the charges are relatively large and thus common errors less on a percentage basis. Though I don't really want to use black powder for other reasons, that's the kind of lattitude I think is good. You *can* make a mistake or have variance and still have a good result.
To that ends, I guess the 4198, 3031, 4895 or Trail Boss Route is the better one.
The old data just intrigued me. Would've never thought of using those powders.
The whole CE Harris line of articles on "The Load" and "Milsurps" was news to me, since I grew up reading pretty much the yellow Lyman manual.
In general I'm not worrying about powder shape... that's the engineers job... but Trail Boss has a shape that is intended to make it bulky and you can't crush it up. So I suspect cut grains are almost as bad. That donut shape, though effective, just strikes me needing extra care. Not a problem at the rate I intend to go. I don't see ever owning anything more complicated than a single stage press. No rush here to crank out 1000's of rounds at a crack.
Thanks for all the good input.
