When Winchester introduced their 300, 270, 7mm, and 325 WSM cartridges a few years ago they were picked up by several manufacturers and sold for a year or so. But the man (Rick Jamison) who developed the idea for the WSM cartridges sued Winchester claiming they had stolen his idea. Jamison had approached Winchester a few months earlier with his idea and offered to sell them the rights. Winchester declined, but the cartridges they introduced were identical. Jamison won the lawsuit and at the time received a royalty for every WSM rifle and box of ammo sold. I'm not sure if that still applies. I know there was a time limit.
Winchester was required to keep manufacturing the WSM's, but Remington and Ruger didn't want to pay the royalties so they developed their own short magnum cartridges that were enough different that they could sell them and not have to pay Jamison.
All of those cartridges will shoot the same bullet weights around 50 fps slower than a conventional magnum in the same caliber. But they are a little more efficient burning less powder with a little less recoil. They are also in short action rifles which can mean a little lighter more compact rifle. In a nutshell it will come VERY close to 7mm RM performance.
But none of the Remington or Ruger short magnums ever caught on. Finding ammo or even brass to reload could be a challenge in the not so distant future. The 300 and 270 WSM's have a strong enough following that they are going to be around. Maybe never an extremely popular cartridge, but they won't die off like the SAUM and RCM cartridges have.
