It occurred to me that perhaps I could tell what caliber my 1873's breech bolt was for by using a cartridge case to compare size. A 32-20 cartridge rim resting on the cartridge support nub at the bottom of the bolt face did not align the primer hole with the firing pin. A .44-40 cartridge case aligned perfectly. OK, now I know it really IS a correct .44-40 breech bolt.
I compared the firing pin to a known model 1873 .44-40 pin that a local gunsmith had in his parts bins. It was a match, so the firing pin was eliminated as an issue. The only thing not fitting in was the bushing in the nose of the breech block. It did not allow the firing pin to go far enough forward, so that is where I decided to concentrate my efforts.
After an extensive internet search I could find no mention anywhere of a Winchester Model 1873 Breech Block Bushing. My only remaining choice was to modify the Bushing I had. One of my older brothers is a lifelong machinist, so I took my Firing Pin, Breech Block, and Bushing to his shop to see what could be done. He has a keen understanding of all things metal, and with an explanation from me of what I was trying to accomplish, he took a few quick measurments with a dial caliper and determined that the hole in the Bushing needed to be opened .005" to accept the firing pin nose, and the Bushing was .040" too long to clear the shoulder on the firing pin. He centered the Bushing up in his lathe, opened the hole with a drill bit, and turned off the length at the threaded portion on the back side. This removed the internal 60° bevel needed for the Firing Pin's shoulder, so he carefully recut the shoulder area back into the Bushing. In about twenty minutes time, I had a recut Breech Block Bushing that accepted the Firing Pin perfectly, and the Firing Pin protruded just the right amount.
I took the parts home and reinstalled them in the rifle. Inserting a primed empty cartridge, the primer fired off just fine. Whew! Another piece of the puzzle solved. Now all I have to do is come up with a Cartridge Extractor, and the rifle will be ready to speak again after who knows how many years.
SHASTA