How to Build a Pen Gun

Co-authored by Hunter Rising

Last Updated: May 22, 2024 Tested

Pen guns fire small projectiles using either the built-in spring or a rubber band and make great improvised weapons that can fit in your pocket. While pen guns don’t fire actual bullets, you can still use them to shoot the ink cartridge tube. With a few simple tools you can find around your home, you can make one all by yourself in a short amount of time!

Making a Pen Gun

Take apart a retractable pen that has easy access to the interior spring.
Put the spring on the writing tip of the ink cartridge.
Put the ink cartridge back into the pen casing backward.
Screw the cap back on the end of the pen.
Press the button to shoot the pen.

Method 1

Method 1 of 2:

Making a Gun from a Retractable Pen

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1
Unscrew a retractable pen to take it apart. Use a pen that easily screws apart with a plunger, or click mechanism, at the top. Separate the top section with the plunger, tube, spring, and ink cartridge. Press down on the plunger to remove the small plastic piece inside the top section. Set all the pieces aside to use later on.^{[1]
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- The ink cartridge is the long white or clear tube in the middle of the pen.
2
Pinch the bottom of the top section with a pair of needle-nose pliers. Take the piece of the pen with the plunger on it and use your needle-nose pliers to bend the tube inwards to make the opening smaller. Pinch the opening in at least 4 places around the pen.^{[2]
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- Don’t bend the area with the screw threading, or else you won’t be able to put your pen gun back together.
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3
Put the spring and the small plastic piece back into the top piece. Hold the top piece upside-down so the pinched end it facing up. Push the pen’s spring into the top first, then feed the small plastic piece you removed earlier into the middle of the spring. Push the piece down until it is stuck in the tube.^{[3]
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- The bent edges on the tube should hold the plastic piece in place. If not, go back with your pliers and bend the edges further.
Reattach the main tube back onto the top piece. Leave the ink cartridge out since you will load it into the pen later as your ammunition.^{[4]
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Feed the ink cartridge into the end of the pen. Hold the pen upside-down, and put the ink cartridge into the pen through the hole at the tip. Make sure the back of the ink cartridge is touching the plastic piece inside the top section. Don’t tip the pen rightside-up or else the cartridge will fall out before you shoot it.^{[5]
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- If the ink cartridge doesn’t fit through the tip, remove the pen tip from the tube by unscrewing it or pulling it off with a pair of pliers.
6
Press down on the plunger to shoot the cartridge. Hold the pen gun sideways so the tip points in the direction you want to shoot. Press firmly on the plunger at the end of the pen to shoot the cartridge out.^{[6]
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- Only point the pen gun at a target. Avoid shooting any person or animal since you could cause them harm.
- Reset the gun by pushing the plastic piece back into the top section and reloading the ink cartridge.

Method 2

Method 2 of 2:

Using a Rubber Band with Any Pen

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1
Take the ink cartridge out of the pen and put it back together. Unscrew the pen to pull out the cartridge if it has threading in the middle. Otherwise, use needle-nose pliers to pull the end and tip out from the main tube. Set the ink cartridge aside before screwing the pen back together again or popping the pieces back into place. Make sure the pen tube is open at both ends.^{[7]
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- Any pen will work when you use a rubber band.
2
Cut the pen tip with scissors so it’s slightly wider than your ink cartridge. Put the tip of the pen between the blades and squeeze the scissors shut. Aim to remove at least ¹⁄₄ inch (6.4 mm) from the end of the pen if you only plan on shooting the ink cartridge.^{[8]
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- Only try to cut the tip if the pen is made of plastic.
- Use a utility knife if the scissors don’t cut through the pen tip.
Use a small drill bit between ¹⁄₈–¹⁄₄ inch (3.2–6.4 mm) wide to make the hole ³⁄₄ inch (19 mm) from the end of the tip. Drill through both sides of the pen using a slow speed so you don’t crack the pen.^{[9]
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4
Feed a rubber band through the drill holes and knot it. Pinch the end of the rubber band and push it through one of the holes you drilled. Pull the rubber band through the second hole until you have the same length on both sides. Feed one end of the band through the loop of the other and pull it tight to secure it.^{[10]
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- If you have trouble feeding the rubber band through the holes, bend a paperclip into a hook and use it to guide the band.
Pinch the plastic end of the ink cartridge in the middle of the rubber band loop. Stretch the rubber band towards the back of the pen until the tip of the cartridge can be fed into the tube. Keep holding onto the ink cartridge and rubber band while you take aim.^{[11]
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6
Let go of the cartridge to fire it. Once the ink is in the tube, release the rubber band and cartridge to shoot it out of the pen. If you want to shoot it again, collect the ink cartridge and reload the pen.^{[12]
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- Avoid aiming the gun at a person or animal since you could cause them harm.