I began my love of cowboy lever guns by buying a '73 short rifle in .44 Special, my favorite handgun cartridge. It was such a heavy little rifle though, so I sold it to fund the purchase of a Uberti carbine in .44 Magnum. It feels much lighter and is so much handier.
I worked up loads in the .44 Special that ran into the 25,000 psi range, same as I use in my Ruger Flat Top Blackhawk .44 Special. Once I reached this pressure level I experienced a case head separation of two, so I backed off a couple of grains which would have put the loads probably in the 18-20,000 psi range. Everything was fine from then on. I attribute the case separations not to the strength or lack thereof of the action, but rather the skinny, unsupported bolt. Anyone familiar with and who have handloaded for the old British SMLE's know this problem well. Those rifles have a relatively small bolt that is supported by only one lug. This causes the bolt to flex which leads to premature case head separation. Just yesterday I was reading an article in an old handloader (1975)in which Ken Waters developed loads for the 38-40. He used an original '92 Winchester and even with that rifle experienced case head separations. He owed this to the bolt flexing under pressure.
I've read a couple of articles/columns in Handloader and Rifle magazines in which they developed loads for the '73 Uberti's. In Handloader #261, the author tested some loads in the 45 Colt using AL2400 that exceeds "book" loads by about 10%. Likewise in Handloader #218 loads were tested in a '73 Uberti .44 Special that exceeded 15,000 psi loads by around 20% with Unique and 15% +/- with AL2400.
Undoubtedly todays '73's are infinitely stronger and safer than those made 130+ years ago as is evidenced by their chambering the .44 Magnum, and for that matter the .357 Magnum which operates at similar pressures. Is the.44 Magnum receiver some "special" hardened receiver? Probably, but one would think from a manufacturing standpoint the logical thing to do would be to make all the receivers to the higher standard.
If it were me, and I wanted to work up the 44-40, I'd do so slowly and carefully. I personally think the brass is going to go far, far before the rifle. Let's not forget that Uberti's, as well as all European manufactured firearms, are required to proofed with a load generating pressure 30% greater than CIP (Europe's version of SAAMI). So that means a 44-40 would have been proofed with a load generating roughly 17,000 psi.
Request a signed letter from the manufacturer that the proposed load is safe in your rifle.
Ha!! They won't even warrant their firearms if they've been fired with handloads!
Keep us posted. This sort of thing is interesting!
CHT