In 1908, Ole H.J. Krag  filed for a U.S. Patent, (954,441), granted in 1910. This allowed one-hand retraction of a semi-auto pistol 'slide', to facilitate single-loading or magazine loading of an empty chamber.

The drawing appears to show a rather generic looking 'blow-back' semi-auto pistol, with Ole's (moving front of) trigger-guard device. There is also a kind of 'Glock-like' trigger.

(As Jeff Cooper would say: "An interesting solution to a non-existent problem").