In the aftermath of World War II, the United States spent 12 years looking for a successor to the M1 Garand rifle. The new standard infantry arm was expected to be select-fire, lightweight, accurate, controllable, and fire a heavy .30-caliber projectile. It would replace not just the M1, but also the BAR and perhaps the M1 Carbine as well - a true universal weapon. Of course, these requirements were complete fantasy, unachievable in the real world - but that did not prevent Remington, Springfield Arsenal, and Winchester from trying to meet them.
This rifle is a Winchester prototype, which has been substantially lightened from the M1 it began life as. A pistol grip has been added, along with a fire selector lever and a box magazine system. A detachable lightweight bipod allows it to be used for supporting fire. I do not know exactly when it was made, but it is chambered for the T65 or 7.62 NATO cartridge, which dates it as definitely post-WWII.
Thanks to the Cody Firearms Museum for allowing me access to film it! Check them out here: https://centerofthewest.org/explore/firearms/