How To Make Gel Ball BB Machine Gun - DIY Homemade Gel Blaster
This build was inspired by NightHawkInLight's series of videos making airsoft BB machine guns from basic parts and trash.
Soda bottle - 24 ounce or larger
Stainless Tube (7.5mm ID)
Gel blaster barrels are usually 7.5mm ID. This will allow a gel ball between 7 to 8 mm to pass through. Most gel balls average about 7.5mm when fully grown. A gel blaster barrel would cost more than a simple stainless tube. I found a 7.5mm ID tube on Amazon, and they cost $15 for 4, so that's only $3.75 each. The 300mm length is plenty long for gel blaster barrel. The tunes arrived straight, but the inside of the tubes was dirty and needed a little bit of cleaning. I use a small piece of abrasive scotchbright pad and a long rod to clean out the inside really well.
Brake Line -
NightHawkInLight used steel brake line for his airsoft BB machine guns. He used 5/16in brake line for airsoft BBs, but gel balls are slightly larger ~7.5mm, so a 3/8in OD brake line is needed). If 5/16in brake line has the same wall thickness as 3/8in brake line, it would have an ID of approximately 6.41mm (0.2525in), which is a too small and would be a tight squeeze for a gel ball (they will break trying to pass through).
Brake line that is 3/8" x 8" to 3/8" x 28" works for gel ball barrel. I measured the ID of 3/8 brake line to be about 7.8-8.0mm (0.3075-0.315in), which is a tiny bit large. THE wall thickness is about 0.762mm (0.03in). It works with gel balls, but delivers poor accuracy and FPS velocity due to air loss around the gel ball. A tighter barrel, like 7.5mm, will perform better.
Where to buy steel brake line: