Dear MDF,
An interesting question, one that I've been curious about myself.
What Terry said is true, certainly of the original 1873 Winchester's. The .44 W.C.F. (.44-40) blackpowder cartridge developed about 15,000 p.s.i. so that is about what the originals are rated for.
Today, the steel that is used in the modern day 1873's is much superior and stronger than the steel used in the originals, so much so, that one of the calibers available for the 1873 Winchester reproductions made today, is the .357 Magnum which is a 35,000 + p.s.i. cartridge!
Having said that however, the .357 Magnum case is much smaller than the .45 Colt. Theoretically, the .357 Magnum case has a total chamber wall internal case area of 1.436" (.357x3.1417x1.28). The .45 Colt has a chamber wall internal case area of 1.818" (.452x3.1417x1.28).
So, theoretically speaking, the .45 Colt has 26.6% more chamber wall internal case area so the .357 Magnum pressure of 35,000 p.s.i. would have to be reduced by 26.6% or a 9,310 p.s.i reduction. Call it 10,000 p.s.i. to be safe.
This means that the .45 Colt at 25,000 p.s.i. puts the same total pressure against the chamber wall that the .357 Magnum does at 35,000 p.s.i.
Okay, what about the thrust of the case head upon the bolt? The 1873 Winchester has a toggle link action which is inherently weak. Let’s see how the pressure against the bottom of the interior of the cases compare. The bottom of a .357 magnum case measures .320” internal diameter . At 35,000 p.s.i. chamber pressure, there is 2,815 .p.s.i. against the base of the case. The .45 Colt has a .430” internal case diameter at the bottom. At 25,000 p.s.i. there is 3,630 p.s.i. against the base of the case. Using this criteria, the .45 Colt pressure would need to be lowered to 19,380 p.s.i. to achieve the same total pressure at the case head as the .357 Magnum, or 2,814 p.s.i.
However, P.O. Ackley proved that the pressure against the chamber walls was sufficient enough to hold the cartridge case in place with little support from the bolt resting against the case head. This is because the total pressure against the case wall is much greater than that against the base of the cartridge as we can see by examining the above data.
What does all this mean? Yes, the .45 Colt, and for that matter, the .44-40 can be safely loaded to higher pressures in a current production 1873 Winchester than in the original 1873’s, but one is on his own if he decides to experiment in this endeavor.
Perhaps the folks that currently produce these rifles, can shed some light on this subject?
Sincerely,
John
