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[Tundra Tiger]

I had to go back to see I was the person who started this thread.

My goal is a modern (Miroku?) rifle and modern loads - something that shoots at 4000 ft pds+, and there is ammo available that achieves that.

 

[fourfive8]

OP’s question- easy answer. Get a Lyman 48th Edition (or newer) Reloading Handbook. Two examples of “pictures for bigger words” attached.

 

[Daryl S]

One way would be to buy a box of THAT ammo and take one or two apart and try to identify the powder & weigh it.
Aside from that, start with max loads for a Marlin lever gun in .45/70, go from there, if pressure signs indicate you can. You will not find the data you seek from any powder company or a loading manual, unless you can find an old AA(Accurate Arms) manual with the red covers. They had the data you are looking for. The top loads for a Marlin .45/70 or .458 Marlin are likely 40,000psi to not over 43,000psi. This 43,000psi is the maximum suggested for the Marlins. The 86 WILL 'take" a bit more. These cases are immensely strong in the head area due to the rim diameter(mostly). Marlin noted some time ago, they loaded a case to 70,000psi and had no problems with the rifle or the case. 70,000 is not loading data, but they did that to show what the rifle with it's small barrel diameter and the ctg. would 'stand'.

 

[Daryl S]

I forgot I had a #51 Lyman book. It lists cast bullet loads for .45/90 in Modern Guns designed for Smokeless powder.
The velocities shown are higher than data for modern Lever Gun .45/70 loads.
385gr. @ 2,134fps
400gr. @ 1,948fps
500gr. @ 1,772fps
535gr. @ 1,707fps
These are the highest vel. posted for these cast bullets.

 

[Don458]

1960 Lyman vol 42 has some general loads. But seems like you’re looking for power load. Let me know if you want the load data.

 

[Rafiki]

I've had my 45-90 Rollingblock shooting 500gr Interlocks at over 2000fps. Shot clear through a bison; way too much power.