They are both very good guns, the SX1 is a great gun after some fiddling. The 50 is a short recoil gun with a floating chamber,there is a tapered chamber that holds the cartridge into a recess in the barrel. The Floating Chamber moves under recoil to unlock, and recharge the gun. The Recoil Spring is in the Butt, and the bolt is adjust by turning a nut like thing housed in the Butt. The gun was design by Marshall "Carbine" Williams.
Model 50s tend to be a little Butt heavy, the floating chamber require frequent and thorough cleaning, and the adjustment of the bolt is different, not hard, just different. But they are good old walnut and steel Winchesters.
The SX-1 was the last "Real" WInchester Shotgun in the opinion of many. It is gas operated and hell for strong. The Buffer needs to be replaced before you shoot it as the originals degraded very quickly, and there are some other minor improved replacement parts that it may need, improved trigger, bolt retaining spring, magazine tubes etc. Don't let this scare you off of one. The only thing you must have is the new buffer and they are cheap.
I own both, and I find I like the Model 50 better than the SX-1, however if I was planning to go out to the range every week for the rest of my life with one semi-auto it would be a SX-1.
Now my good friend Ole Cowboy will be by soon I expect to tell us what I missed
In the meantime go to the link below, and search around on the SX-1, for the rest of the story.
http://www.shotgunworld.com/bbs/viewforum.php?f=60&sid=593786e71359cbc5c6b654bb56bfb806
