If you remove the forend, the recoil spring is underneath. There is a metal (brass/bronze/steel) ring around the mag tube. This is designed to allow the use of high base, or low base shells depending on whether the friction ring is against the receiver, or at the far end of the mag tube.
Here is some good info that I pulled off of "Shotgunworld.com"
"The heart of the Browning long-recoil system is the friction ring assembly. With enough friction, the action works without beating itself up. Too much friction causes malfunctions, and too little leads to excessive felt recoil, a cracked forearm and broken internal parts"
For Browning, Rem 11 and Savage 720. "The standard shell guns will have two friction rings, one of which is a two part assembly. The steel ring is beveled in the inner edge like the beveled gas ring of an 1100, but is solid, and without a gap in it. The bronze ring is segmented on its indside face, and has a spring steel clip-ring around it. The bronze ring and its steel clip-ring each have a gap."
"On the standard guns, there are three settings that all the literature mention, heavy, light and lightest. By far the largest number of guns are left in the heavy configuration, and work well that way. The heavy configuration is with the recoil spring on the magazine tube, then the steel bevel ring over the spring with the bevel towards the muzzle. The bronze friction ring with its steel clip-ring goes on next and then the barrel hanger. Once the forearm goes on, the bronze friction ring is sandwiched in between the bevel of the rear ring and the bevel machined into the rear face of the barrel hanger.
"Upon recoil, the two bevels act to squeeze the friction ring against the magazine tube. The heavier the recoil, the greater the friction."
"The other two settings for the standard guns are light and lightest. However, I have never had to use them. The light setting simply takes the steel bevel ring and moves it from between the recoil spring and the bronze ring to between the rear of the spring and the receiver. Obviously, back there it does nothing to influence the amount of friction. It rests there simply to keep it out of the way without losing it. I have never used it because every gun I have fired worked fine in the heavy setting, even with 3 dram target loads. However, if your gun does not cycle with the light target loads and the friction rings set in the heavy configuration, change the rings. While I always had good luck with my various A5s and clones (a total of nine guns I owned, and several hundred customer guns) yours may be different. And, I test fired them all with a 3 dram equivalent handload. You may be using a target load that is even lighter."
"The lightest setting for the Browning A5 (Rem 11) is meant for shotguns with a Cutts Compensator installed. The Cutts is an external choke combined with a recoil reducing cage. In the Cutts setting you remove the bronze ring entirely, and leave the steel ring in back of the recoil spring. (Why not sotre the bronze ring back there too? The bronze ring wold prevent the barrel from recoiling all the way back in its proper stroke.) The extra weight of the Cutts unit i only part of the reason you have to decrease friction. When the wad and shot leave the muzzle inside the cage, their recoil generating work is done. When the wad and shot strike the choke, they jerk the barrel forward. On any other shotgun the forward force would be imparted to the whole gun, dampening felt recoil. On the A5 the force is imparted to the barrel, decreasing its ability to cycle the action."
He recommends to set it to the heaviest configuration that will work to avoid cracking the forearm and other damage.
From Gunsmithing: Shotguns, by Pat Sweeney. If you have a Rem 11 or Browning A5 or Savage 720 you should own this book.