Failed attempt at a silent TB launcher

[lozz08]

You need to understand what makes the noise in the first place in order to understand how it is silenced, Hilo.

Spudguns make a bang because the gas that pushes the projectile out of the barrel is at a different pressure to the atmosphere, even after it leaves the barrel.

When you fire a spudgun, the gas that is travelling down the barrel is decreasing in pressure, because it is being exposed to more empty volume in the barrel.

If you use the right amount of gas to fire, it's pressure will have dropped to the point where it is equal to the pressure outside the barrel when it exits, and so, in theory, there won't be a bang.

[Technician1002]

Since this thread is kicked up again, I did some more testing and confirmend that GGDT was correct in stating the barrel is too long. With pop cans the drop in speed is dramatic. When testing the ability to demolish empty pop cans at 100 PSI the 3 foot barrel provided reasonable power on the 1 inch valve on the Marshmallow cannon.

This pop can was launched at the edge of the handle on a propane tank. Trying the same thing with the 7 footer at 100 PSI yielded very disappointing results. The much slower launch is evident in the lack of damage to the cans. I tried twice. The center can was launched from the 3 foot barrel and the two outside cans were launched from the 7 footer. Why the 7 foot is so quiet with a tennis ball with an obvious vacuum is still a mystery to me.

Note the obvious slight implosion on both cans on the sides.

The mass of the tennis ball still provided a decent launch at 110 PSI, but pop cans don't do so well. Does anyone have a clue why it was quiet?

Another can launched from the 3 foot barrel provides an interesting wrecked can.

[Hilo]

The mass of the tennis ball still provided a decent launch at 110 PSI, but pop cans don't do so well. Does anyone have a clue why it was quiet?

If I'm interpreting the results from GGDT correctly, changing the mass of the projectile will also change its position within the barrel, at a given pressure. For example, a 50 G projectile may be at about the 1" position at 32 pounds. A 100 G projectile may be at 12" at 32 pounds. If the barrel is 12" long, the 100G projectile would make no noise since muzzle pressure = atmospheric pressure. The 50 G projectile, on the other hand, would make noise since the muzzle pressure would be about 22 lb, creating a vacuum.

Is this correct? I'm trying to determine if I understand how to figure it out.

[jackssmirkingrevenge]

A heavier projectile will accelerate at a slower rate, giving the propelling gas more time to expand in the barrel and therefore lowering the pressure when it eventually exits the muzzle. The speed of the valve is also a factor here as it also affects the rate at which chamber pressure falls and barrel pressure rises.