I am going to be casting some bullets for my 45-70. These will be cast and sized to .457" diameter.
My question is, in order to shoot them out of my .45 caliber muzzleloader I would have to reduce them down to .451". Is this feasible with and alloyed bullet? I know .006" isn't much but can it be run through a die with busting a gut in the process?

Lots of lube, and 3 sizing steps - knocking it down 2thou at a time. You'll get there, no sweat, and no busted gut. You can most likely get there in 2 steps, 3thou each, but I've tended to get better results by going 2thou.

I size jacketed bullets for my .357/44, lube them up and crank them through. Use a single stage O-press with plenty of leverage, they'll all run through fine.

Thanks for the info NoMercy. But I'd have to buy 2 more sizing dies to go .003" at a whack at about $25 apiece just for an experiment to see how well they would shoot.
Now if someone would could run some through their dies if I sent some that would be great.

What is your alloy? How hard is it?

the ones I will be casting for the muzzleloader would be pure lead (4.5 BHN). I guess I should have mentioned that in the initial post.
The ones for the Sharps replica will be in the 8-9 BHN range.

Pure lead will cast smaller than a given alloy? Just how much? You shall have to cast a few to see.
.oo6" seems like very little until you try running it thru a sizer die !
It seems like a good project to try but it,IMHO,just isn't worth it!

I often wondered why manufacturers picked .458" as the diameter for a .45 cal centerfire rifle chamberings and .451"/.452" for 45 cal handguns and muzzleloaders. Why couldn't they make it all uniform? Marketing I guess.

bronko22000,that would be a good thing for you to research and find out why and let us here know how come!
I would think the rifle bullet has to stand up to a lot more pressure for a longer time than a hand gun bullet so it has to be bigger?

If that were the case then why is there cast bullets as small as .22 cal?? I don't think that's the reason.

I called Sierra Bullet Company. Well,no one there has any idea why either ??????????????