The gas cylinders, pistons, magazine tubes, and slides are all different between these two guns, but they still function in the same way.
There is a small hole in the bottom of the barrel, which, when the gun is fired, vents gas from the burning powder into the cylinder. This in turn forces the piston rearward, which clobbers the front end of the slide and causes it to move backwards. This causes the bolt to open, extracting and ejecting the empty shell, and feeding another round from the magazine, if one is present.
At that point, the action spring takes over the work. It forces the slide (and thus the bolt) forward, chambering any round which may have been fed from the magazine.
In order for all of this to work, the gas piston should be a loose fit in the cylinder, and it's normal for it to slip back and forth with a slight clunk as you point the barrel up or down. This is a good thing! If yours doesn't do this, or if you've been having problems with the functioning of your rifle, then now you need to make a decision.
Take a look at the following steps, and decide whether you are able (and willing) to perform these operations. If not, then put ol' Betsy back together and tote your firearm to a qualified gunsmith to have it thoroughly cleaned, and don't forget to mention you'd like the gas port and cylinder assembly to be included in the cleaning.
