Two diameter GG bullets

[Don McDowell]

Richard as you are just getting started, I would really caution you to keep it simple. If you don't want to go with the bullet I use from BACO then simply go with the lyman postel.
There's an awful lot of internet fluff tossed around about the 45-70 not having "enough case capacity" and like most things if someone with a large post count posts something then it has to be real, whether or not that person even owns a rifle , or if he does, even shoots that rifle is another question that seldom brings a satisfactory answer.
With the energetic powders we have available to us from Swiss, Schuetzen and others, the case capacity of the 45-70 is more than adequate to produce velocity enough to shoot to 1000 yds just fine.
You mentioned a bullet that shoots well at the rams might not shoot at 1000 yds, this is an especially true statement when folks try to push more bullet than the twist in their barrel can stabilize. This will become more pronounced if there is wind present.
All this was laid out for us over 100 years ago, and all we need do is don't over think this stuff.