Follow the Hodgdon recommendation strictly: precisely the same brass, primer, bullet, powder, powder charge, case length and so on.
Any change in these variables can jump pressure markedly.
And therein lies the bugaboo: too many reloaders don't follow the load precisely and get into problems.
Also, be very aware that every gun is an individual. I have a Marlin 1895 .45-70 I bought new in 1977. The oft-quoted load of 53.0 grains of IMR3031 under a jacketed bullet creates excessive pressure in this rifle.
It may not in yours, do so in your neighbor's, and yet be perfectly fine again in a rifle clear across the country.
Each gun is an individual. Too many reloaders forget that.
I am very wary of any loads listed on the Internet, especially those recommended on sites that do not belong to ammunition, powder or component manufacturers.
Too many reloaders toss about loads, especially high-intensity loads, without regard to the individuality of guns or listing the specifics.
Never, ever use a load off the internet without checking it against a reputable, recently published reloading manual or the website of a company that publishes reloading manuals.
Also, just because the .444 Marlin and .450 Marlin MAY work at 40,000 CUP the .45-70 may not. And there may be a very good reason the manufacturer why it won't. I'd suggest you contact Marlin and ask if it can be loaded the same pressure as the .444 or .450 Marlin.
My personal philosophy: Heavy, maximum or near-maximum loads are not needed in the .45-70. A 400 grain bullet at 1,700 fps will take anything in North or South America.
The .45-70 was reliably killing elk, moose, grizzly and buffalo at under 150 yards when its 405 gr. lead bullet was propelled at 1,200 fps.
The .45-70, because of its rainbow trajectory, is limited to 200 yards, preferably 150 yards maximum, in the game fields.
The 350 gr. bullet at 1,800 fps is plenty for big game. If you need more power, use the heavier 400 or 420 gr. bullet at 1,700 fps or so.
