I've always thought, for power beyond the .45 Colt loads the SAA is capable of, the .357 was the best choice due to the cylinder thickness. Mr. Johnson's post illustrates my thoughts well...
In theory, that makes sense. In practice, it requires much more chamber pressure in the 357 to come close to the observed game killing power of larger calibers at lower pressure/velocity.
The 44 spl ended up being a number of peoples choice to split the difference between larger caliber and chamber wall thickness for a useful increase in performance in the Colt SAA's. What many seem to consider insane level loads worked out by Keith and others was in the 19,000-20,000 CUP level (250 gr/1150-1200 fps), while the early 357 factory loads were in the 40,000 CUP or above level, and were shown as a 158 gr @ about 1500 fps from an 8 3/8" barrel. The slightly reduced 44 spl loads in the newer solid head cases that came out in the 50's gave slightly less velocity and slightly more pressure, the increased pressure being in the low-mid-ish 20,000's, but was still deemed quite acceptable by all the relevant authorities (NRA, Lyman etc) on reloading of that day. The 44 spls just chugged along nicely at that velocity/pressure level and gave a very noticeable improvement in power and range from the sedate factory loads that were really nothing more than a smokeless 44 Russian load from the black powder period. I find loads in the 250 gr/850 fps range very nice for most shooting, with getting to about 1000 fps gives noticeably flatter trajectory out in the open (to several hundred yards) and still very pleasant to shoot. The upper end loads I save for carry in bear country.
BTW, shooting black in the 44 spl is an absolute blast! I used to shoot black in my 4 3/4 nickel 44 spl. The echo of the report was very different than smokeless loads. The smokeless loads were a flat crack, at any level, compared to the deep booming report of the black loads, that seemed to have a rolling echo off the surrounding hills. The load level isn't that great compared to what can be gotten into a 45 Colt case, but is enough to shoot small game and have a ton of fun. With smokeless, the 44 spl case is a bit more practical and efficient unless looking for absolute top end, Ruger level loads. I've had flaky ignition in the 45 Colt with light-ish powder charges and lighter bullets. The 45 Colt case is best with the standard weight bullets and a charge that doesn't leave a lot of air space. Shooting a couple hundred yards, there was a noticeable difference in elevation consistency when I used such loads.
When attempting to duplicate the loads from "back in the day", keep in mind that both Unique and 2400 have changed somewhat since then, and loads should be worked up with a chronograph, not just taken as grain for grain loads from older sources. They may be just fine, but they are likely producing a little more pressure/velocity than the old loads did. Unique is fine for the medium range of loads, the top end Keith type loads should be with 2400 or H-110, though I have no data for H-110. I'm still using "old" Unique and 2400, so haven't had to convert loads to the modern versions of those powders.
