The Winchester Catalogue No. 81 (dated 1918) shows that the WRA factory loading for the 25-20SS used an 86 grain bullet with 19 grains of Black Powder.
You could duplicate this black powder loading with enough rounds to obtain chronograph data, and then work up some factory equivalent loadings.

Max load in a 44 depends a LOT on how well set-up the rifle is.  If the breechblock is tight to the shoulders in the frame, and locks up to the breech face with .003" to .005" interference, it can take regular loads of twice what a rifle that is loose can handle.  By tight, I mean that the breechbloch-to-shoulder fit will trap a feeler gage made from 0.4 mil plastic film, (.0004").   When the shoulders are loose, so that they take none of the thrust load, it is all thrown on the linkage and the pivot pin. Due to the angle of the linkage, the load on the pivot pin, is amplified to about 1.5 times the direct load at the breech face.   Been studying on this issue for some time in the context of the "lugged hammer" feature that some early 44s chambered in .32-40 and .38-55 were given.  

That said, a "loose" 44 probably is capable of handing black-powder pressures only in the .25-20 cartridge.  Say, 12K psi, or 1400 fps using the 86 grain bullet.  Quickload says that equates to about 6 grains of AA#9 (my pet load) or 8 grains of 4227.  

Properly set up, the old 44 should handle double that pressure in the .25-20 cartridge, (Quickload says about 8 grains with the same powder and bullets), with relative ease, even without the lugged hammer.   

I'll have much more to write on this subject as time goes forward.  Chuck Deats has been kind (and clever) enough to generate some free-body force diagrams, which are the basis for the above statements.  Here is the most basic variation.  Keep in mind that this analysis takes no account of elastic deformation, and thus can only be considered an approximation.

MT Chambers wrote on Mar 16^th, 2015 at 10:29pm:


Running some Quickload scenarios, I find that the pressure needed to push a 120 grain bullet to 1450 fps through a 24 inch barrel is only a bit short of 15000 psi.  Still well within the safe range for a properly fitted 44.  Indeed, even a not-so-well-fitted 44 would probably take it for several hundred rounds. Stevens did, after all, keep on chambering for the .32-20 right into the 1930s.  Unless there is an underlying problem such as a pre-existing crack in the frame, it appears that the failure mode is that the breechblock fractures at the pivot bore.  (John Taylor has posted pics of such.) No catastrophic blowup such as the notorious Quigley-Ballard incident.  Now, if the 44 is chambered for .40-65 as that Ballard was, all bets are off.  Although I recently bought a 44 that had been rebarreled to...(wait for it)... .45-70!     Don't know how many times it may have been fired, but it's not the wreck that you might expect.