After Jonathan Edward "Ed" Browning had his 1929 rifle dropped form US military testing, he took the design back to his shop in Utah and kept working on it. By 1938 he had made enough improvements that he was ready to present the gun to Winchester, hoping they would be interested in purchasing the design. Specifically, he redesigned the receiver to move much of the bolt travel into the wrist of the stock, shortening the action. He also replaced the short recoil action with an annular gas piston. He made two sample rifles, one in military configuration and one in sporting configuration.
Winchester was looking for a self-loading rifle to market at the time, because they could see that war in Europe appeared to be imminent. They had been caught without a military rifle of their own during World War One, and did not want to be in that situation again. They thought that Ed Browning's design showed merit, so they agreed to purchase it, and brought Browning onboard to help continue development.
With Winchester's resources, it was possible to make the guns more professionally. Winchester designated the rifle the G30, and we have one of the examples made by Winchester in the video as well.
The tilting bolt mechanism took inspiration from John Moses Browning's 1911 pistol, and the trigger housing bears an interesting resemblance to that of the French Berthier rifles (which may or may not be coincidental). The rifles appear to have worked reasonably well, although the annular gas piston was a hindrance which Browning apparently was unwilling to abandon. With his death in 1939, the project moved on to a new phase with David Marshall Williams taking on the job of improving it.