This prototype carbine was designed by Eugene Reising, and produced by the Harrington and Richardson Arms Company. It was basically a copy of the H&R Reising submachine gun chambered in .30 carbine, and shared many of its 48 parts with that weapon. It weighed 5.81 pounds with a sling and 5 round magazine, and had an overall length of 38 inches with a 15 inch barrel.
The gun was acceptably accurate, simple, and durable. However, its overall functioning was poor due to a large number of ruptured cases. Manual operation was difficult when attempting to clear malfunctions (it was often necessary to hit the butt against the ground or shooting table to open the bolt), magazines fed poorly, and the gun was not tolerant of non-uniform ammunition.
Thanks to a Ronaldo in Brazil, we also have a series of color photos of another example of this rifle. You may notice that this example is slightly different. In addition to the scope, it has an upper handguard and sling attachment reminiscent of the final military version of the M1 Carbine.
We also have an article on the H&R/Reising carbine written by Sgt. Gary Paul Johnson, who had the opportunity to test fire this prototype (reprinted with his permission – thanks Gary!).