In this tutorial you will learn how to make a semi-automatic rubber band pistol out of K'NEX.
Depending on the rubber bands you use, the gun can hold up to about 8 rounds of ammunition. One shot is fired for each pull of the trigger.
In a previous Instructable, I shared a design for a large Rubber Band Gatling Gun (link will open in a new tab).
I realize that while it is more impressive than this pistol, a lot of people might not have enough pieces to make the Gatling gun. This pistol is one of the most basic semi-automatic rubber band gun designs I have, and it still looks good and works well. It can also serve as a starting point for many other rubber band guns (including the Gatling gun).
Step 1: Some Notes Before We Start
Throughout the instructions I will refer to certain pieces, mainly the rods and connectors, by a color in order to specify their size or shape. The colors I refer to will usually be the original colors used by K'NEX for these pieces (see labeled photo above). However, keep in mind that a given piece will often be available in more than one color, and that the photos in my instructions will often feature these multiple colors. I may or may not make note of the color difference in the text. I may also refer to the shape (e.g. a "circle" connector = a "white" connector). In general, the color that you use won't matter as long as the part is the same size or shape, unless I explicitly say otherwise.
Note that I've decided to make this gun entirely from metallic pieces because it looks cool that way.
There may be instances where you don't have an exact part that I call for in the instructions. If this is the case, use substitutions as appropriate. I will try to provide some guidance for certain aspects of the build, but I can't accommodate every unique situation you may face, and so I will trust that your common sense will guide you through the rest.
I use some spacers (e.g. blue spacers and silver spacers) in this build. Following from the discussion on substitution, keep in mind that one silver spacer equals three blue spacers, so you can always make that substitution if needed. If you don't have enough spacers, you can try to use something like a small grey connector to replace two blue spacers, as long as the size of the connector doesn't get in the way of something else. However, there are places where you will need at least some blue spacers, so if you don't have any, you may be out of luck unless you are willing to cut some connectors in half. If you have none, I would highly recommend buying some before starting.
I suppose I should also throw in the obligatory "don't use the rubber band gun on people or animals" statement. However, let's be realistic here - you're going to want to shoot rubber bands at your friends, your parents, your little sister, and pretty much anyone that walks through the front door, right? Just use common sense if you do - don't aim for the face, make sure your targets are willing participants, and it helps if you all wear some safety goggles. And leave your pets out of it. I won't be held responsible for any damage you cause with this thing.
Now, if you're ready, let's get started.
Step 2: Starting the Handle
Start by making/gathering the parts shown in the photo. I've provided some close ups of the larger assemblies.
Note: The silver spacers (and one blue spacer) on the larger assemblies in the top of the group photo aren't technically necessary. However, I find that they make the handle more comfortable to hold.
Step 3: Handle (cont'd)
Next, connect the bottom ends of the two assemblies shown with the orange connector.
Step 4: Handle (cont'd)
Then, add the other assembly between the first two, connecting with a white rod as shown to the bottom of the left assembly. Line up the top grey connector of the middle part between the top grey connectors of the rear part.
Step 5: Handle (cont'd)
On the top of the rear side, slide a blue rod through the three grey connectors along with the two blue spacers as shown.
On the top of the front side, slide a blue rod through the two grey connectors along with 4 blue spacers between them.
The handle is now complete, and you can set it aside while we start the next part.
Step 6: Barrel
Start the barrel by making the two identical halves as shown in the photo. Note the gaps in the top edge where it looks like two white rods should go. Leave those empty - we'll fill them in a later step.
Note: It's important to use the blue connectors, as opposed to white ones, at least toward the rear, since we need that extra space they provide. I later realized that the front blue connectors could be replaced by white/circle connectors without affecting the design, so it's your choice.
Step 7: Barrel (cont'd)
Next, connect the front ends of the barrel halves together with a white rod, and then add on the additional yellow connector and white rod shown.
Step 8: Barrel (cont'd)
Add a red connector to each side of the white rod below the yellow connector. Then, fill in the gaps on each side with the green and white connectors as shown.
Step 9: Barrel (cont'd)
Assemble the grey connectors, white rods and blue spacers as shown (two each). Note that the grey connectors are facing opposite directions (probably not necessary, but I like the symmetry). Now, remember those gaps I told you to leave empty in the first barrel step? Add this part to the front-most gap at the top edge of the barrel.
Step 10: Barrel (cont'd)
Similarly to the previous step, assemble the orange connectors, white rods, and blue spacers shown (two each), and then add it to the second gap on the top edge of the barrel assembly. You'll notice that the barrel now has a taper to its width.
Step 11: Add the Handle
Now, take the handle you made previously and connect it to the bottom of the barrel assembly at the green and white (black shown) connectors.
The gun now looks like a gun. The remaining steps are just adding in the mechanical bits and pieces to make it work.
Now assemble the grey and red connectors and blue rods (two each) as shown, and attach the assembly right behind the handle on the white/circle connectors.
Now make the assembly shown (two red connectors, two blue and two silver spacers, and a blue rod), and attach it to the previous part off the back of the gun. The rod with the spacers should be on the bottom, and the free end of the red connectors are attached to the free ends of the blue rod from the previous step.
Then fill in the gap between the red and white/circle connectors with green rods (black shown, both sides).
Now make the two parts shown. The first one is made from two green connectors, two white rods, two blue spacers, and a small metallic blue connector. Unfortunately you can't substitute a tan lock here since the small pin would get in the way. If you don't have the metallic blue piece, you could cut off the pin from a tan lock. Preferably the tan lock has a round top and not a square one.
The second part is simply a yellow rod with a light grey connector connected to its middle.
Now connect the two parts from the previous step into one assembly as shown. Note the direction of the light grey connector.
Then, gather two blue spacers, a blue rod, and two metallic blue connectors (you can use tan locks here instead), and use them to attach the previous part to the back of the gun. The blue rod goes through the red connectors on the back of the gun and through the green connectors on the previous part. A blue spacer is placed on the blue rod in the gap on either side between the red and green connectors. The light grey connector should be towards the top/front.
The previous part should now pivot with respect to the gun assembly about the blue rod.
Step 16: Trigger
Next, assemble the trigger as shown. Then assemble it into the gun assembly. The blue rod of the trigger assembly goes through the green connectors in front of the handle. You'll have to temporarily disconnect one of the green connectors to get the trigger in (sorry!). The trigger should pivot, and the yellow rod moves within the space between the blue connectors.
To hold the trigger in, cap off the ends of the blue rod with metallic blue connectors or tan locks.
Now, make TWO of the piece shown above.
Then, add a silver spacer to each end of the yellow rod at the rear of the gun. Push them in toward the center.
Now, add one of the diamond-shaped pieces to each side of the gun. The light grey connectors at the corners pass over the yellow rods at the rear of the gun and the trigger. Cap off the end of each yellow rod with a blue spacer and a grey connector a shown (both sides).
Give the trigger a wiggle. It should move the pivoting piece at the rear of the gun.
Now make the piece shown and attach it in front of the trigger, under the blue connectors. the black piece should point to the front. You could use something other than the black ball-end piece here. Ultimately, a rubber band has to be able to wrap over it.
Step 21: Spoke
To attach the spoke, assemble the parts as shown. Slide the blue rod through the light grey connectors at the rear of the gun, along with the spoke assembly and two silver spacers (one on each side). Cap off the blue rod with the metallic blue connectors or tan locks.
Note: The black pieces between the white rods on the spoke fill in the empty gaps in the circle connector and help to hold the white rods in tight. Otherwise they might break out under the stress of the loaded rubber bands. As an alternative, you could also cut some green rods in half and snap them in instead of the black pieces. This may be a better option since they get less in the way of the rubber bands as they slip of the spoke when fired.
Now just add an extra blue rod to the yellow connectors in front of the orange connector portion. This adds some extra reinforcement to the barrel.
Step 23: Finishing Touches
Finally, add a rubber band between the trigger and the black ball-end piece to bias the trigger forward. Then, wrap a rubber band around the tip of the barrel. This will prevent the ammunition rubber bands from wedging themselves between the yellow connectors at the tip.
Step 24: How to Load and Fire
Congratulations, your pistol is done! Now it's time to load and fire it.
Start by placing a rubber band over the tip in the opening of the front yellow connector. Then, stretch the rubber band back and place the other end on the spoke BEHIND the small black piece. I wouldn't recommend putting the rubber band in the notch of the small black piece as it would place too much torque on the spoke once all of the rubber bands are loaded.
Cock the spoke back until it catches and the next black piece is presented. Then repeat the loading process until you have the desired number of rubber bands loaded. How many you can load will depend on the rubber bands you use.
To fire, simply pull the trigger. Depending on the rubber bands you use, and whether or not you used the small black pieces or something with a lower profile (e.g. cut-in-half green rods), the rubber band should fire on either the initial trigger pull or once you let go. Each pull of the trigger will fire one rubber band.
Step 25: Conclusion
Hopefully by now you've got a nice new rubber band pistol. This gun is small and simple, but it serves as a building block for many other rubber band guns. You can easily extend the barrel, add a stock, change the handle, add a scope, etc. Feel free to modify it to your heart's content.