Thepitchedlink, I have one of those, they are a fine handling, lightweight gun in 28 gauge.
Unscrew the nut at the end of the fore end and remove the fore end wood by pulling forward. You should see the recoil spring with some rings at the front end.
There should actually be 3 rings, a silver one (smallest), a brass one (largest) and a black one. The black and brass rings are split, the silver one is not. Pull the rings off and look at the silver one - you will notice that the ring is flat on one side, and beveled on the other. This is important.
The silver ring is the load regulator. It is the first ring to be put in place, it should be in direct contact with the recoil spring. To shoot normal 28 gauge loads (3/4 oz.) the beveled part should face the spring. To shoot heavy (1 oz.) loads, the beveled part should face the muzzle. Take a minute to get it right.
The brass (largest) ring goes on next. It is identical on both ends, you cannot get it backwards. Finally, the black ring goes over top of the brass ring - again, no backwards installation is possible.
Once the rings are in place, pull the bolt back until it locks open. Keep the gun pointing up so that the rings do not slide off. Slide the barrel on and apply some pressure to compress the recoil spring an inch or two. While holding the barrel in compression, slide the fore end wood on and screw on the nut.
A note about the nut - if you screw it on too tight and go shoot the gun, it will be a real bear to undo. Get the nut firmly seated, but do not apply a lot of torque or you will need pliers and a rag to get it off again.
The fore end wood is thin and can be easily damaged when not on the gun, so keep the wood attached even when the barrel is off, as for storage.
Another thing you will need to know is that the magazine feed only works when the gun has been fired. If you try to unload an unfired gun, the shell in the chamber will eject, but shells from the magazine will remain in place.
To get the shells out of the magazine, close the bolt, turn the gun over and press the bolt release button. This allows you to stick your finger in the feed gate and press on the piece of metal on the inside of the receiver, on the same side as the bolt. The shell(s) will pop out. This process is more difficult to describe than it is to do.
It really pays to play with the choke tubes and the loads you want to shoot. Go to a patterning board and try the different tubes with your shells, there can be large variations in the pattern depending on the load, more so than with a 12 or 20 gauge.
One final bit of advice - check the tightness of the stock bolt. For some reason they are not firmly bolted down from the factory. Just about every one I have seen needs tightening. Just remove the butt pad, get a big screwdriver an snug it up.
Properly set up, the gun is very rewarding to shoot and a delight to carry. I use 3/4 oz. loads exclusively, I never found satisfaction with the 1 oz. loads. Grouse, huns and farmed pheasants can't tell the difference anyway.
Enjoy the gun and shoot it in good health.
(Corsair, the gun is recoil driven, not gas, but it is similar in concept to the A5.)
Sharptail