-This is my first inscrutable- please don't be to harsh...
So what I did in this instructable is made a mine for airsoft out of a normal sprinkler.
What you're going to need:
Any size sprinkler longer than 1 foot long
A 3/16 or 13/64 size drill bit
Step 1: Step 2
So first what you're going to want to do is disassemble the sprinkler, you simply unscrew the top and remove the insides. The next thing you want to do is cut the long piece found inside with the spring wrapped around it down to about 1 inch below the larger top.
Step 2: Step 3
Then take that same piece that you cut and remove with the pliers the small white thing in it. After you do that put it down the sprinkler about 2/3 of the way down and drill a hole through it as shown in the next photo.
Step 3: Step 4
Place the spring in the sprinkler, align the small piece that you cut with the hole at the bottom of the sprinkler and screw the top back on. Then push the piece down with a small pipe or something so that you can kind of see through to the other side and push the nail through like so. Beware- it is a little difficult to get the nail all the way through, but if you do it right, you can do it.
Step 4: Step 4
Place a stick, wooden steak, or something like that in the ground pointed to the target, secure the sprinkler to it and fasten some string to the nail and connect that to a stick on the other side of the trail. Simply place the bb's down the top of the sprinkler. The goal is that when a person pulls on the string, the nails gets pulled out and releases the bb's.