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Supersonic Nerf Cannon

submitted by Mordhaus

5 years 12 months ago

A few more thoughts on the Nerf Cannon.
Yes, I know if I used a longer barrel I could get higher speeds, but I did not want to deal with a 20ft long gun. I think a 6ft barrel was enough to show what a supersonic nerf dart can do.

Davekni got a pingpong ball going 2000mph which is 2930 ft/s!! (mach 2.5). His barrel was 20ft long. It can shoot through 3/4in plywood! You can see that video here- https://www.youtube.com/watch?v=5xuwu...

I always thought the speed of sound was the limiting factor, because the flow 'chokes' at mach 1. Its a big controversy among air-gunners, and theres like a 900 post topic on it here https://www.gatewaytoairguns.org/GTA/.... Some guy got one going like 2100 ft/s which I thought was impossible. https://www.youtube.com/watch?v=qUq4O... So it prompted me to do some research.

It turns out flow does choke at mach 1, but its only the mass flow that chokes. The gas can still expand supersonically.