The Winchester Model 50 Shotgun is an interesting artifact. Other than the aluminum alloy trigger guard housing, the piece is constructed of machined, forged-steel parts. No less than David “Carbine” Williams (of WWII M1 Carbine fame) was responsible for the operating system, that used a “floating chamber insert” very similar in both design and execution of the more famous Colt “Service Model Ace” or their Government Model .22 “Conversion Unit” that allowed inexpensive practice once upon a time.
The Winchester Model 50 Shotgun represents a transition of technology of sorts. Up to this point, other than the aforementioned Auto-5, all repeating shotguns from Winchester used a tilting bolt that locked into a receiver mortise in its inside-top surface. Think “Winchester Model 12.” This is a very solid way to lock the bolt, but it is quite a bit more difficult to properly manufacture, compared to what is today’s standard, a bolt that locks into a barrel extension.
The Winchester Model 50 Shotgun is a technological “half-step.” In most recoil-operated arms, the bolt is delayed from rearward travel by the weight of the barrel that is affixed to it, and the barrel recoils a short distance with the locked bolt before the bolt’s timing allows it to disconnect from the barrel on its way back in full recoil.
The Model 50 Shotgun instead uses its floating chamber insert as the locking abutment as well as the piece that moves rearward, leaving the barrel “fixed.” As the bolt and insert move to the rear, a portion of the gases envelope the outside of the bottleneck-shaped insert that help “float” the assembly rearward via that gas pressure.