Hello BKS, I have checked the following and verified by scale (weighing).
If you are using a jacketed 350 grain bullet (I use Hornady 350 Grain RNFP's and RN's, I think they make them in HP's as well) ahead of 2400 I have found info for a starting load of 2400 of 27.0 grains and a Max load of 29.0 grains (conservative IMO). I have settled on 28.0 grains with great results.
My newer 45-70 Lee Loader has a 3.1 cc scoop in it which is too large for 2400 powder. My older set of lee powder scoops indicate a #129 scoop at 28.5 grains of 2400 but for me on my equipment it is closer to an even 28.0 when weighed. I believe the #129 scoop corresponds to the newer marked scoop numbered 2.5 cc.
If your scoops are numbered in cc's check how much 2400 a 2.5cc scoop throws to verify it is advertised at 28.5 grains, if so, you are GTG.
Have fun and all the best....<><....
I do not, and never have, used any over powder wadding when reloading