In the latest issue - Jan / Feb 2012 of Bear Hunting Magazine, Ralph Lemayer has his article on .458 SOCOM that reads, in part:
"The rising popularity of the AR15 and its rapid move to the dark timber has generated a need for that kind of muscle in the AR. Other cartridges like .450 Bushmaster or .50 Beowolf were created to fill this void and they are fine cartridges that get the job done, but they both require the rifle be modified. Parts need to be changed to make them function. Buffer springs, unique magazines, different bolt, etc. are all required.
The real cleverness in the design of the .458 SOCOM is that nothing need to be changed but the upper; same magazine as the .223, same buffer spring in the buttstock, same everything. Just get a .458 upper available from Rock River Arms, Teppo Jutsu or other custom builder, get loaded ammo from SBR Ammunition, Corbon or Reeds and go. Your .223 AR has just morphed from a varmint getter to a full-fledged bear stopper by simply changing the upper and no new FFL transfer required. Basically, one gun with two barrels."
What a load of crap!