The airsoft land mine that I bought was a pitiful waste of $50. The self proclaimed "loud boom followed by a large blast of powder" was a tiny pop and half inch high puff. Enemies didn't even notice that they triggered it. Frustrated, I built a better, more powerful mine. It's easy to replicate and simple to use. It shoots BBs twenty-eight (28) feet and powder six (6).

Step 1: Materials.

This project is fairly inexpensive, depending on the materials you already have. I only had to buy the springs.

You will need:

1 inch diameter pipe.
3/4 inch diameter wooden dowel.
3/4 inch diameter washer.
3/4 inch diameter spring (ID # C-756).
Screws, 1/4 inch diameter.
Fishing line.
Smaller dowel.
Small metal dowel.
Suitable safety pin wire.

Step 2: Cut to Length.

Cut your pipe to lengths of 61/4 inches, or about 21/2 inches longer than your spring. Cut your 3/4 inch diameter wooden dowel into 3/4 inch length plugs. You will use two of these plugs.

Step 3: Build the Mechanism.

This is the heart of the trip mine. The device acts like a piston, the spring is compressed and held in place by the pin. When released it springs back, inertia causing the contents to fly out.

First you need to drill a 1/8 inch guide hole through the center of both your plugs. Use a clamp to hold the plug in place. Now for the tricky part. Place your 3/4 inch washer over the base of your spring and line it up with the plug, try to make it as flush as possible. Tightly screw the washer and spring in place, you can do this through the side of the spring. Repeat this for both ends of your spring.

Step 4: Safety Pin Hole and Securing the Mechanism.

Stand the pipe upright and drop your mechanism inside. Push down the mechanism as far as possible with your smaller dowel (the plunger). Keep your thumb on the dowel where it meets the end of the pipe. Remove the plunger, keeping your thumb on the spot, and place alongside the pipe. Mark where the end of the plunger is, this is where the compressed mechanism will end. Remove the mechanism from the pipe so it does not get in the way of the drill bit. Drill a hole with a diameter equal to the safety pin through both sides of the pipe, slightly above your mark. This will account for any error.
. Reinsert the mechanism, making sure it slides smoothly. Make sure that the base plug is flush with the bottom of the pipe. Drill a guide hole through both sides of the pipe and plug, roughly 3/16 inch from the bottom. Secure the mechanism with a screw on both sides of the pipe.

Step 5: Finishing Touches.

Search the house for an appropriate safety pin. I was lucky enough to find these beauties. Cut the pin to length with wire cutters. It should pass through the pipe with about 1/4 inch to spare.

Epoxy a 71/2 inch metal dowel slightly below the pin hole. This serves as a stake, allowing the trip mine to be secured to the ground.

Use another small wooden dowel for the tripwire's stake. Whittle one end to a point and split the other end. The tripwire will be fastened to the split. Tie the other end of the tripwire to the safety pin.

Optional:
You can spray paint the trip mine to blend in with it's surroundings. I did a base coat of black and misted light green over it. The prototype is a base paint of green with a mist of black. I used some ghillie left over from my ghillie suit to further camouflage it. You can also attach local flora with a black rubber band.

Step 6: Operation.

As I said, this is basically a piston. It uses inertia to fling it's contents out of the pipe. Plant the trip mine at roughly a forty-five degree angle. String out the tripwire and plant the stake on the opposite side of the path. Push the mechanism down with the plunger and insert the pin. Make sure as little of the pin as possible is holding the plug in place. Then pour the appropriate amount of BBs and powder into the trip mine.

View the video below to see the trip mine in action. _{YouTube's quality is horrible, I'm using Metacafe instead.}

This is the detonation of the trip mine at 1200 frames per second:

Step 7: Measurements.

This land mine shoots baking soda an average of six feet with one spoonful, but the powder effect isn't as impressive. I find that two spoonfuls is a good balance between distance and powder effect. Three spoonfuls would be good at close quarters, it will cover you with powder. You're victim won't know what hit him.
You can pour a good amount of BBs into this, I'd say about twenty or thirty. These average twenty-eight feet. Combine BB's and powder for the best effect.