This thread has been quiet for awhile but I have read it with great interest.
This is one mans opinion and rational for limiting the Marlin 45-70 to 40,000 psi.
I have read that one before and yet some of his loads are over 40,000 CUP.I think someone mentioned his load data is 45,000 or less for the 45-70 as you can see with a 400 grain bullet going over 2,000 fps out of a guide gun.
Something else interesting is the requirements of a dangerous game cartridge for Africa.4500 ft lbs of energy and they say a levergun can't do it? Rick Jaimeson tested the 450 Marlin in a 24 inch barrel.One of his loads was a 300 Nosler with 2488 fps and 4124 ft lbs of energy with 40,900 PSI.Now thats in a 24 inch barrel as most mags are.You have about 3,000 PSI to play with and you have to reach 2600 fps to get the 4500 ft lbs of energy.It can be done but it would probably be a hair over the 43,500 PSI but very shootable in the 1895 action and probably under the 45,000 that some manufactureres load to.
Just my opinion.Jayco.
http://www.real-guns.com/Commentary/comar52.htm 
