A Ruger patent for a “Firearm Barrel Retaining System”, filed in 2009, was published by the USTPO yesterday. The patent application (#20120017483) describes a quick change barrel system that includes an old school machine gun carry handle that help facilitate hot barrel changes.
I wonder if Ruger had planned to enter a quick barrel change variant of their SR-556 into the Marines IAR competition that was won by H&K.