First of all avoid using Magnum Primers unless the reloading data says so.

And second, find out what other shooters shooting competition are using then verify the load and carefully start working those loads up weighing each load.

Of the reloading books to have, Hornady 3rd Edition is a must and I cross reference it with Lyman. I haven’t found any errors in them, But I strongly recommend you do need Hornady 3rd Edition, Lyman, IMR Reloading data, Winchester and Hodgens. You can down load IMR reloading from their web site.

The Ruger #1 and the Ruger #3 I would use Magnum primers because you can pump up the loads on these two.

I prefer Federal 210’s for what you’re doing and runner up is Winchester Large Rifle Primers.

Back in 86 when I found I was going to Alaska I started to buy a 45-70 instead I bought a 444 Marlin. Reloading for the 45-70 is probably the most cautious cartridge I know of due to make and model you have. Examples of max loads are below for using what I’ve found to be common load throughout the loading data I’ve found and I will list the Reloading Book, Rifle and the Primers used. Please note, depending on the fire arm used the load is different as to whom did the research and development of that load. Also notice the reloading data for the Ruger #1, this fire arm you can “HOT ROD”!!! Bill Ruger owner of Ruger Firearms tried to blow up a 45-70 Ruger #3. The stock was busted in 3 places and melted the casing in the chamber! But I don’t think I would even go there!!!
Reloading book Lyman
Rifle: Springfield Model 1873 Trap Door
Primer: Remington 9 ½ Large Rifle Primers
Bullet Weight 300 Grain
Powder: IMR4198 Max load 36.0 grains at 1647 fps
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Reloading book Lyman
Rifle: Winchester 1886
Primer: Remington 9 ½ Large Rifle Primers
Bullet Weight 300 Grain
Powder: IMR4198 Max load 41.0 grains at 1779 fps

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Reloading book Hornady Third Edition
Rifle: Springfield Model 1873 Trap Door
Primer: Federal 210 Large Rifle Primers
Bullet Weight 300 Grain
Powder: IMR4198 Max load 42.5 grains at 1900 fps
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Reloading book Hornady Third Edition
Rifle: Marlin 1895
Primer: Federal 210 Large Rifle Primers
Bullet Weight 300 Grain
Powder: IMR4198 Max load 51.2 grains at 2100 fps
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Reloading book Hornady Third Edition
Rifle: Ruger #1
Primer: Federal 210 Large Rifle Primers
Different weight listed 350 Grain
Powder: IMR4198 Max load 53.3 grains at 2200 fps
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Reloading book Hornady Third Edition
Rifle: Ruger #1
Primer: Federal 210 Large Rifle Primers
Different weight listed 500 Grain
Powder: IMR4198 Max load 47.6 grains at 1800 fps

If you intend to utilize any of their powder you
can also download a good source of informaion from Hodgdon's website. Easy to use and lots of choices which are well documented by the company and its somewhat exchaustive testing. This data is handy to cross reference with that obtained from your manuals when working up loads. This does not apply to Clay's statements but don't bother using just anybody's loads without first checking them for yourself.

Repeat, Hodgdon and IMR powder numbers are not interchangeable.

Jim in Mo

Hodgdon and IMR powder numbers are not interchangeable

My stupid Brother found that out the hard way, the bolt had to be forced open