Just like nobody can sight in a rifle for you. ...somebody else's pet load will probably not be the most accurate lod for your rifle.. even if it the exact same make and model.
IMR 4198 and H 4198 are not the same powder.. you cannot substitute the data for one for the other.
Some reloading books describe the rifle used to test the loads published in that book.. make model barrel length some don't.. some reloading books give specific info on type of primer, make of brass, as well as bullet design and powder weight... you cannot substitute cast bullet data and jacketed bullet data.
So start with load data that is somewhat close to your rifle's spec's barrel length is the most important spec .. and as you know from what you have posted so far .. with 45-70 there is old gun data and modern gun data.. make sure you are using the correct chart
Some reloading books give a range of powder weight and some only give the max permissible load. Either start with the lightest published load or 10% less than the max load.
Divide the weights of powder into 6 to 10 equally spaced powder weights ... ie. minimum published is 30 grains and max is 40 grains then 1 grin increments ... max is 35 grains back off 10% starting weight is 31.5 grains .. you break it down into 8 weights .5 grain apart.
You load 5 rounds at each weight between starting weight and max weight.
You shoot the 5 rounds at each powder weight at it's own target and you label that target as to powder charge bullet weight date . This is important you inspect the brass for any over pressure signs, even the first and lightest powder weight before you move on to the next higher powder weight
http://www.massreloading.com/reading_pr ... signs.html if you see pressure signs YOU DO NOT SHOOT A HEAVIER CHARGE you stop shooting
You continue shooting each group of 5 into it's own target inspect for pressure label target until you run out of loads or see pressure signs.
You then take each target and lay them out on a table lowest to highest powder weight in order.
Examine the groups .. you will notice they will either get larger then smaller of smaller then larger.. and you may also notice the point of impact/ center of the group may move around on each target... this is because different powder loads will change the rifles barrels harmonics and different velocities will affect the speed of rotation of the bullet. .. You may see the groups get larger then smaller again .. with 45-70 I would go with the smallest group with the lightest charge
if you have to choose between two equally small groups. that would be your roughly most accurate load.... but that will only be true to the extent that you use Identical components and powder... change you brand of primer .. you got to start all over .. some buy powder in the 8 pound jugs and when they start a new jug they go thru the whole rigmarole all over again .. but definitely if you change brand or style of bullet ( even if you keep the weight the same) or brand or type of primer.
Okay now.. if for some reason you need extreme or maximum accuracy .. long distance shooting or competition .. hunting ... or if you just happen to be a very accurate shooter to start with, and want the most from your weapon
You do a second round of test loads using the weight of powder you used in the target before you smallest group target and go in 0.1 grain increments up to the powder weight used in the target right after the target with the smallest group shoot those in sequence lowest to high and apply the same analysis .. if you are going to do the second round for max accuracy... then any time you change any component you really should start over .. consistency is accuracy when it comes to reloading. Folks who are going for max accuracy also as a minimum sort their bullets by weight and only use bullets closely matched by weight for any serious work. Some also sort their brass by weight.. I don't do that.. I do use all the same brand of brass for accuracy work.
I sort bullets into three groups, first I sort completely by weight 0.1 grain increments .. I usually get a long line of bullets across the table with identical weight lined up one behind the other vertically .. I make a reasonable decision and cull out the very lightest and very heaviest bullets .. it's a judgement call.. there is normally some resemblance to a bell curve weight wise and how picky I am depends if there will be money involved.. either prize money or side bets ... if it just beers, I'm less picky also depends who I am shooting against or how badly my ego needs strokes.
Hope this helps.. if anything is not clear, please ask questions, and I will do my best to clarify .
if you see pressure signs YOU DO NOT SHOOT A HEAVIER CHARGE you stop shooting