This is for a short range, high volume airsoft shotgun. It fires 50-60 pellets, depending on how many you load. It's small, so it's very maneuverable, but has a limited range of about 25 feet.

Step 1: Materials Needed:

Stuff needed to start:
1: A spring. This needs to be stiff enough to fire the pelets a good distance, but not so stiff as to make it impossible to load. Best test is if you can compress it to half it's length with your bare hands, it'll work ok for this.
2: A length of PVC pipe. it needs to have an inside diameter that will fit your spring tightly, and a length to completely hold the spring when its not compressed, plus about an inch.
3: A 1/4 inch bolt that is 1.5 inches long.
4: Two nuts that fit the bolt's threads
5: A retaining pin. This can be any kind of pin, but I recommend getting one with some kind of safety devise to keep it from working it's way out. You'll see what I'm talking about later on
6: Some cardboard
7: Lots of ammo.
8: Some kind of tube or rod to fit inside the PVC but not inside the spring.

For Tools:
It can be made with a hacksaw and a 1/4 inch push drill, but a Dremel and a power drill help a lot. Also, unless you like the 'plumber' look, some spray paint helps.

Step 2: It Begins!

To start, cut a 1/4 inch chunk off, put this aside till later.

Step 3: Drilling

To start, drill a 1/4 inch hole at the bottom of the PVC pipe. Make it about 1/4 inch from the bottom. Drill another 1/4 inch from the top. The third hole you see will come in a few steps.

Step 4: Sprangs!

Next, put the spring in the PVC and push the bolt through the spring, locking it in place. Put the nuts on and tighten them together to lock them into place. You can also use a lock nut if you want, but I like being able to take it apart and put it together without replacing the nylon nut every time.

Step 5: Third Hole!!

Now that your spring is locked into place, take whatever thing you used to compress the spring and do that. Hold your thumb against the compressy-tool and hold that against your pvc to figure out where the spring stops compressing. this is where your retaining pin will go.

Step 6: Retaining Pin

This is the pin that will hold the spring in place, till you pull it and unleash plastic death on those in front of you. The wire clip is what I was talking about for the safety. It keeps the pin from being pulled until you remove it, and is also re-usable, making it cheaper to operate.

Step 7: Fixing the Pushy-compression Tool

Use your Dremel or hacksaw to cut a notch into the end of your tool thing. this is so you can compress the spring and put in your retaining pin, then remove the tool.

Step 8: Cutting Your Cardboard

Remember the 1/4 inch chunk you cut? use this as a stencil so you can cut two circles of cardboard that will fit inside your PVC.

Step 9: Assembly!

Put a cardboard circle in on top of the spring and use your compression tool to press it down. Insert the retaining pin and pull the compression tool out. It should look a bit like the first pic. Then, pour in as many pellets as you think it can fire. Then, push the second cardboard disc in with the compression tool. Now, when you want to fire, just pull the pin out. It took me four tries to hit a target at 10 feet, but after mounting it on a weapon, this is the spread I got with it. I figure range to be 25 feet at best.