I shy away from proprietary calibers. There as many other cartridges that do the same job the .300 RCM. With oddball calibers, unless you handload, you cannot be guarenteed a steady supply of ammo.
G - Guns, PG - Plenty of Guns, PG-13 - More than 13 Guns.
"Though defensive violence will always be 'a sad necessity' in the eyes of men of principle, it would be still more unfortunate if wrongdoers should dominate just men." - St. Augustine