I originality got the Idea to make this after testing out the "Nerf Shotgun" instructable on this site. Half way though testing I thought "What if there was such thing as a Nerf mine?" I then searched the internet for such a device, but to no avail. Thus I made one, for under $2.

This is the first generation, I posted this so you guys can improve it.

You will need:

1 Roll of duct tape/ hockey tape
3-4 Small confetti launchers ("Party poppers" they can be bought at the dollar store.)
1 Wooden board, just use anything lying around.
4 Nails/ Screws
3-4 Pins (Need one for every party popper.)
2 Spikes (anything that can be stuck into the ground easily.)
Strong string, anything that cannot be ripped apart.

-Tools
A Drill
Scissors
A Hammer (If using nails)
Needle nose pliers (If pin is not long enough)
A lighter (if using the plastic string I used) NOTE: Not the string I used in the picture.

To take apart the confetti launchers

Pop it first
Take the wrapping off
Pull down at an angle on the back of it. (The side with the grooves on the outside)

It is pretty obvious how to reset it once the back is off, so I wont explain it.

Step 1: Duct Tape

First cut 2 strips of tape and put them across the confetti launcher as shown in the first picture.
Next place 2 strips of tape parallel to the tube,on either side. Over lapping the ends of the previously placed duct tape, as shown in the second picture.

Repeat 3 or 4 times (Try to leave a little room between each confetti launcher, it makes re-setting easier.)

Step 2: Pins & Holes

Drill a hole in every confetti launcher at an angle, your drill should be almost touching the confetti launcher in front of it. The holes should all be going the same way, the higher side holes should be on the same side on all launchers. (Refer to pictures 1 and 2)

Next attach one end of the string to the pins, tie it or melt it as long as it holds up to a strong tug. (I used around 50 feet of some plastic string I found in my garage.)
There should be little to no slack in the string between the pins, when fully inserted.

Picture 3 is what it should look like from the front after you get the pins in.

Note:
If your pins are not long enough, just spread one apart and straiten the prongs out. Then put a small loop in one end. (Pictures 3 and 4)

Step 3:

Last step, screw or nail onto the sides of your board the steaks.(Pictures 1-2)

Some darts will go farther than others, so keep that in mind.
The launchers I used are not that powerful thus I had to put it at such a weird angle.
45 degrees from the ground should work best for most of you.
The darts should travel in a sweeping motion across the ground, this should bring them into your foe's chest/ lower body.
Don't let the darts go too low or too high, they will be ineffective this way.

At this stage I suggest you give it some camouflage, it is kinda obvious left in this state.

In the final picture Is what It should look like when it is done, I am currently trying to add motors to it so it can be a wireless device or tripwire activated, thus the extra space on the board. (Sorry I forgot to put the pins in, but the holes are there)

To fire it just reset the launchers,
Then put the pins in
Next move the innards of the launchers to match that of a "fired" launcher (Turn the back until it gets to the point of where it should fire when you take out the pin)
Cram darts down the front of each launcher, 6 wiffle darts per launcher works best.
Finally, pull the string like you are starting a lawnmower.

Range

14 - 15 feet, unmodified.