The .44 magnum is the final descendant of the moribund .44 American. The .44 American was .44” being a heel based bullet like the .22 Long Rifle. When S&W got a substantial contract to produce breaktop revolvers for the Russians in the late 1800’s, the Russians stipulated that the bullet should be more enclosed by the case, which reduced bullet size to .429” and became the .44 Russian cartridge. This was later lengthened and called the .44 Special around the turn of the century. The .44 Mag, introduced in 1955, is the Special once again lengthened and hot-rodded.
Slim, where does the .44-40 fit into there. Its my understanding that it was the fore-runner of the .44 special...which is one of my personal favorite pistola rounds.