Harrington & Richardson was one of the main contractors for the M14 rifle program, and they also had been a major producer of the M1 Garand rifle. In particular, H&R had produced a .22 rimfire training rifle to mimic the handling of the M1 Garand, which was adopted by the US military as the MC-58. When H&R got into the M14 game, they figured they could easily adapt the MC-58 into a training rifle for the new M14.
In May 1958, H&R proposed the “Simulator, M14, .22 Caliber, Mark I” to the US military. It was tested that summer, and in December 1958 a report issued on the trials. The Simulator was not ultimately adopted, and only a few prototypes were made of which this is serial number 1.