We made a NERF chaingun fire about as fast as a 7.62mm M60 Machine gun. That's around 500 rounds per minute (RPM). We did two major modifications, increasing the voltage to the firing motor, and adding a round counter and a paint job.

The total cost on this hack was about $79

Step 1: What You Need

For this modification, you need the following:

Upping Voltage:

1 x Nerf Vulcan EBF-25 ($50)
2 x 9.6v battery packs
2 x 9.6v battery pack connectors (RadioShack)
2 x Alligator clips
3 x Wire nuts
1 x Ballpoint pen
1 x Chopstick
1 x Mana Energy Potion
1 x A hint of stupidity

Painting/LED Mod:

1 x LED counter from QKit ($18)
1 x Lever/Roller microswitch
1 x LED
3 x Momentary pushbutton switches
1 x 12v miniature battery
1 x Coil of wire
1 x Various paints

Step 2: Cranking It Up

The first modification was to increase the voltage to the motor. More voltage with available amperage means a faster spinning motor. Faster motor means more rounds down range, or into a co-workers face, as the case may be.
The Nerf Vulcan EBF-25 starts with a requirement for 6 D-Cell batteries. That's an expensive number of big cells. When wired, they yield about 9v.
To connect the battery packs to the gun, we actually had to make a little tool. The power terminals are too deep inside the gun to clip on the alligator clips, so I took apart a ball point pen, slit up the side, put a compressed alligator clip in it with the lead hanging out the slit. I put the alligator clip on the battery terminal and then pushed a tie-wrap (or chopstick) through the back of the pen, slipping the alligator clip out and hooking it on to the power terminals. it worked like a charm.

Step 3: Wiring the Beast

Hook the battery packs together like in the photo. *WARNING: If you hook this up wrong, you could dead short the battery packs together which could make them explode or do other scary/injurious things.* Hook the negative power terminal from the gun to the black lead on pack A, hook the red lead from pack A to the black lead on pack B, and then hook the red lead from pack B to the positive power terminal on the Nerf gun. Voila. It's done. Now separate the alligator clips with a piece of cardboard to keep them from shorting. Stuff everything back into the gun and close the door. Now you have a 500 round per minute cube warfare weapon of mass destruction.

Step 4: Adding the LED Round Counter

It took me about a half hour to solder together the counter from QKit. A big part of that time was trying to figure out which resistors were which, so make sure you have a guide before you start. Instead of using the microswitches from QKit, I soldered leads from their locations on the circuit board to pushbutton switches mounted on the gun. The three switches are Set, Program, and Reset. The LED comes on when you run out of ammo, which was accomplished by just hooking it to the "out" pin on the counter.

Step 5: Add the Counter House

We took the top of the ammo box off and used it to house the counter. Dremel out the spot for the LED counter out. We dremeled part of the chain-gripping assembly to mount the roller switch. This way the links would hit the switch each time the belt advanced. The leads from that switch go to the counter through holes Dremeled in the top of the chain guide.

Step 6: Paint the Gun

This was accomplished with a base matte black primer coat, and then metallic silver paints mixed with various levels of black to give variety to the metal pieces. Put metallic silver on black parts that would show wear, like behind the charging bolt or near buttons. This was our variation, but the sky is the limit with design possibilities.

Step 7: Attach Round Counter to Finished Gun

Take the round counter and insert it into the dremeled out top piece. This can be accomplished with velcro, or another adhesive. There is enough room to tuck all wiring underneath the casing. Attach the top piece to the body of the gun, and you should be all set.

Step 8: Fire Away!

Now that everything is set, switch the gun to automatic and have a blast! Literally.
You can check out the video of our gun in action here:

We are also giving away a 12-pack of mana to the first person to send us a video of getting this gun past the elusive 600RPM mark. Details are in the video. ****UPDATE***** Someone already won the contest. Thank you everyone for trying!

Disclaimers:

1) We're not affiliated with Nerf, Radio Shack, QKits, Dremel, or anything else you saw us use to build this. Mana Energy Potion is the exception, because that's who we are.

2) There's a very real danger to doing this mod. Dead-shorting battery packs like these can cause them to explode and injure you. Nerf even has a "Do not modify this dart blaster" warning on the gun itself. That's where we used the Dremel to cut out the panel for the LED counter.

3) You will probably ruin your Nerf dart blaster. We could smell the motor burning when we fired it with 4x the voltage. Eventually, the motor coil will probably melt. Also, the gears will probably strip out.

4) Don't paint over your orange tip. That's illegal as far as we know. Fortunately, the orange tip is separate, so you can paint your gun and then attach the orange tip.