I'm shooting the BTB 355gr sized to .432 in my micro grooved 444 over 44gr of reloader 7 . works awesome, good accuracy, kicks like a mule and put a 2 inch hole through a deers neck with no bloodshot meatI had a 444 but unless you get a fast twist one, you are limited to the bullets you can use. Microgroove barrels don't like cast bullets generally. The one I had had a 1:38" twist, so 265gr bullets were about its limit. Hornady is not making the 265gr .429" bullet anymore, so I sold it. If you do get a .444, make sure it has a 1:20" twist and ballard rifling.
The 45/70 was the easiest of the three to load for. (getting components) and achieving consistently good accuracy.
I owned a 450 marlin for 1 year, and found it too expensive to shoot. (getting brass was hard, and factory ammo was expensive .......................if you can find it) I ended up sticking with the 45/70 so I could use the big-ol' cast bullets.
I was under the impression that the silenced .458 used by the military was an basic unaltered M-70 .458 with a can on it, but I would have to dive into the books to confirm that.
With respect to the microgroove .45/70, in those days I was using plain base bullets backed with 3031, so I have no doubt that accuracy would be improved and fouling would be lessened with gas checked bullets.
COTW mentions this one in thier chapter of military rifle cartridges.
It actually was 458x1.33inch or thereabouts IIRC. Used a 500 gr FMJ apparently.
Did not endear itself to snipers. Too heavy according to field reports. I think I vaguely remember Wilson Arms(?) A Georgia based dealer in Class III firearms in the late 1970s. Saying that they tried out a suppressed 458x2inch(?) rifle and the suppression factor was outlandishly successful. No other details. Thier own words.
I've heard from a good friend that it was a 458 wm used with 600 gr subsonic round under 1000 fps. He has replicated the round with cast bullets and the accuracy is very nice. I'm not sure who made the 600 gr jacketed bullet or what it's profile was like.
The 458 whisper is a shorter version of what was used in veitnam