Rock Island Armory 56789: Rock Island Armory has taken the 1911 from a basic one-caliber design to a well-optioned, high quality, multi-caliber design over the past three decades with the development of the XT series. Intelligently engineered with a pinned solid state barrel design and delayed blow back slide that rivals accuracy. The XT series is backed by Rock Island Armory\'s closely-managed, hand-fitted quality process and created in 4140 steel.