Hello Tim,
I want to cast my own. The story I hear is that the nose needs to fit the bore dia well or it slumps to one side when fired giving poor accuracy. An old timer cast me some nice bullets many years ago. They were the 500 grain Lyman govt style bullet. The nose is very sloppy in every 45/70 I have tried them in. They do not shoot very well either.
If the bullet isn't seated straight in the case, or doesn't fit the bore well to begin with, you're gonna have accuracy issues. If a load has a noticeable bulge in the case on one side that's not even all the way around, the bullets aren't seated straight and that will definitely get things off to a bad start, and is a common complaint with cast bullets in the 45-70. A deep rifled Ballard bore would probably be more forgiving tho, but I've not shot one, so have no personal experience with them cept in muzzleloaders. I've shot numerous cast bullets in my 45-70 and 45-120, haven't had accuracy issues yet, but I choose bullets that are proper for the bore. My next bullet will be 700gr Ranger Ricks in both the .500 S&W Handi and 45-120, the .458" may not shoot well, but I'll give em a try anyway, they're bore riders I'm pretty sure.
Tim