Elgin Gates developed a range of SuperMag cartridges based on the 357 Maximum case (OK the truth is slightly more complex and contraversial, I'm not going there today).
This is what it looks like, flanked by a standard 357 Magnum and a 30-30. Note the extremely short neck.
The 270 SuperMax has a much longer neck.
300 Bellm Whisp-R case, 270 Max / SuperMag, and a 5,6x50R case.
One load for the 7mm SuperMag
139 grain Hornady #2820 17.5 gr S265 Federal small rifle primers
The Super Mag Story scanned from Metallic Silhouette Shooting, 2nd Edition, downloaded from http://dwcollectors.org/dwca-content/articles/414_Gates_Super_Mag_Story.pdf and more on the 357 SuperMag / Maximum
"Paul Gauthier 12-23-2003, 08:22 AM I have one caliber in my TC Contender in that new cases must be annealed before the first loading. It is the 7mm Supermag. This caliber died a quick death after being intro'ed as the next best thing to sex. But I got a brand new barrel and redding dies real cheap so I fool around with every now and then. It's made from .357 Maximum brass necked down to 7mm with a 1/8' neck and 90* shoulder. Case life is almost non existent. Accuracy sucks to say the least. That little neck just ain't got enough surface to hold the bullet concentric. But it is LOUD, you can sure impresse your friends with muzzle flash and noise. A longer barrel might help, only got a 10". But it came and went so quickly that I don't know if they ever made any longer.If I remember correctly it was intoduced to compete with the 7mm TCU, The only difference is the supermag has more case capacity. I haven't been able to determine if that is a plus or a minus as I don't have a TCU. I think there is little doubt that either case has enough capapcity to properly utilize a 7mm bullet. Later."