Metallurgy has come a long way in the last decades, and it was not until such became much stronger that S&W started to even think about building magnum revolvers.

Hence the 45acp has the same working pressure of a colt 45 long, being it only 18,000psi.  The Colt 45 longs where loaded with black power, and when the smokeless power came along, since it required less case volume to achieve the same pressures, the ACP was born (rimless and to the same working pressures since at the time, it was about the max that the frames/pistol could withstand).  

As for mag loaded 45 colt long loads, if you take a good look, will come to understand that it was not until Ruger built a 45 colt long hand gun that could withstand these higher than 18K pressures that any loading data hotter than 18k PSI data loads where published (and only to be run in the Ruger hand guns).

So on that note, if you are looking to build a magnum hand gun, then start off with a frame that the Metallurgy is new enough/ designed to withstand mag pressures.

As for the 1917 frame, reserve it for the standard 18K psi loads that is was design to withstand.