Open the gun. It needs a smaller phillips head than most Nerf guns. You have to pry off the orange pieces on the back of the gun and on the front (between the pump and the gun itself, you can see it hanging there). The barrel assembly is not shown, but you don't have to take it out yet.

Slide the pump plunger all the way out. On the end of it is a little hole. Plug it up. There are also little holes on the sides of the plunger; these should be plugged as well.

Take the barrel assembly out. This is the bottom of it. See those little holes? Those are where the screws are that hold this thing together. Take them out.

Now that the screws are out, you can take the black thing out. Save this: you will need it later.

Take the barrels off. This takes some doing. Most of them should just pull out, but one or two might be glued in real tight. I whacked these with a hammer. It doesn't matter if they get broken--you won't use them later.

Now comes the hard part. Using a hacksaw, cut the barrels off. Make sure you don't cut the thing in the middle. This thing houses a spring that allows the barrels to rotate. Also cut your PVC barrels: use 1/2" sched 40 PVC and make the barrels about 5" long. Much longer and the gun won't be able to get the darts out, but this length gives good range and accuracy.

Get out your hot glue gun. Put hot glue on the bottom of one PVC barrel and push it on. Make sure you line it up correctly. Hold it on for a minute, then spread more glue around the edge of the joint. It should be relatively solid, but don't press on it. Make sure the barrel is straight; if it's not, pull the barrel off and try again.

Here, all four barrels have been glued on. It should look pretty straight like the picture.

Now, you need to put the black thing on. This will help hold the barrels straight and prevent them from coming off. Because of the black thing, we don't need to use epoxy; it holds the barrels well enough that hot glue is enough. You will need to sand it a little to get it to fit over the PVC, but it's not that hard. I did it with a little piece of sandpaper that I shaped into a cylinder.

Put the new barrel assembly in and hook everything up the way it was.

Close it up. Now you have a super long range sniper rifle with a great ROF in a small package! It shoots stefans great--this was my main objective. It works really well for me.