Machine Gun - Dual Barrel

Assembly:

I got the inspiration to build and design this project after seeing anti-aircraft cannons, and their dual barrel mechanism to double their rate of fire. I wanted to transform this idea into a 3D printable toy that has a high rate of fire. This mechanism uses dual rack and pinion mechanisms with incomplete gears so the hammers can be pulled back, and once the gear runs out of teeth, the hammer is enabled to fly forward and launch the 3D printed bullets. 

The magazine is also powered by a single rubber band, this is so that bullets can move downward fast enough and evenly to not disrupt the motion of the hammer. The sliders in the magazines exist to help push them deeper into the barrel and also to get a little more power at lower levels.

The print profile contains brims for tall and skinny parts (Like the bullets), and for very long and skinny parts (Cannons and firing hammers). You should use a blade like a boxcutter to remove them, or some cutters work okay. Ensure the finish is smooth at the bottom.  Without the brims I have experienced disruptive warping.

You can put as many rubber bands on this thing as you like, with the only tradeoffs being how hard it is to pull back and how much it might hurt if you have an accident. I personally prefer 2 per cannon as it is a good balance for firing power vs ease of use. 

I highly recommend you print some targets or use stacks of cups to shoot at, it makes the print far more enjoyable to use, and you can also test other models on your printed targets.

Safety notice

• I am not responsible for any misuse or modifications that could cause harm to anyone, do not aim at people, pets, or anything that is dangerous.  
• Keep out of reach for children under 3 years old. The small parts could present a choking hazard.
• Adult supervision is recommended for children or young users.
• Only operate the toy manually and do not motorize or automate it.
• Do not reach into the gears
• Ensure you are not using very old and used up rubber bands, doing so can result it in snapping unexpectedly. 
• Do not put an extreme number of rubber bands on each launcher (4-5+)