The Historical Firearms blog has a very interesting post on a forgotten John Browning patent for a (then-advanced) pump-action shotgun. The weapon features an enclosed hammer, dual extractors, and a tilting locking block reminiscent of the later M1918 automatic rifle. The gun in many ways foreshadows the “Perfect Repeater” Winchester 1912, but differs in a few tantalizing respects. First, the bolt locks via a separate block, like a BAR or MAG, not via tilting the entire bolt as in a Model 12. Secondly, the firing pin is raked at an angle, apparently to accommodate the low profile rear receiver. 

The design was never produced; Winchester bought the patent (as they did 43 others) from John Browning to ensure no rivals could use it to make a competing gun:

Browning’s relationship with Winchester was such that the company rather than paying him a salary paid for individual designs.  This was done to keepBrowning’s designs out of the hands of rival manufacturers.  As a result only ten of the forty-four designs purchased were actually produced.  Many of the designs were differing mechanisms and advancements of firearm types already in production. In the case of the shotgun patented in 1896 – if another company such as Remington had purchased the patent then Winchester would have had a major rival who was selling a similar, if not superior product.

The purchase of John Browning’s designs meant that Winchester was able to hold its nearest competitors at arms length while they sold some of America’s most popular shotguns and rifles, including the M1885 lever-action shotgun, the Model 1894 lever action rifle, the Model 1897 pump-action shotgun and a series of extremely popular .22 rifles.

Many, if not most of John Browning’s patented ideas did not get produced. This fact is a bit staggering how many not only did get made, but were pivotal in the history of small arms development.