This is one of my two 357 Super Mag (Max) Martini Cadet carbines I built. It has a 14" twist barrel, same as a Contender, aprox same pressure rating, depending on when the story was written and by whom it was written. I use the 200 RN and 200 grain RCBS cast FN bullet and 180 grain Sierra bullet in it with H-110/296 with Small Rifle primers.
The cartridge was designed by, developed by Elgin Gates for the use of heavy bullets, all of my SM 16 Revolvers and 4 SM single shots used heavy bullets well enought to win many matches and I used H-110 because it was cheaper than 296, but the same powder, also 4227 was a very good powder. Been shooting the Super Mag for more than a few decades. Steve Vogel, Ex VP Ruger sent me two, first month production guns a 10" and an 8".

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“To expect defeat is nine-tenths of defeat itself. It becomes a self-fulfilling prophecy. It is best to plan for all eventualities then believe in success, and only cross the failure bridge if you come to it."
Francis Marion - The Swamp Fox