SpudFiles

Here it is in pure pneumatic configuration and somewhat finished, the epoxy is more or less cured but I'm giving it at least another 24 hours before further testing.

You're not going to get much higher velocities than you already are anyway. Don't you just hate the speed of sound problem?

What kind of damage can it do with a .12 gram?

very nice. how loud is it?

Nice gun jack. I pondered the same thing earlier today. Think you could break the sound barrier?

Nice velocities,only 12 FPS off the sound barrier(Sea Level)if I remember correct.There is no reason why you couldn't break the sound barrier,but could you be getting incorrect results from having the chrono to close the the muzzle?I did that with one of my pneumatics and I thought I broke the sound barrier but I was really about 200 FPS shy.

The reason that he couldn't break the sound barrier is because he is using room temperature air. Unheated air will not push a projectile past the speed of sound under normal circumstances.

DYI wrote:The reason that he couldn't break the sound barrier is because he is using room temperature air. Unheated air will not push a projectile past the speed of sound under normal circumstances.

Not necessarily. As it's being pumped in, the temperature will have risen quite a bit.

It's also not impossible to achieve supersonic air currents in a smooth enough barrel. If the pressure differential at the valve is high enough, and the projectile is really light, the supersonic air currents generated at the valve could continue down the barrel. And if your airflow is supersonic, you can get a projectile to go supersonic.

Take something like this MTU.
That uses supersonic airflows to generate vacuums. (Actually, that 6.3mm version might be useful to enhance a BBMG...)

With that C:B ratio, the smoothbore brass barrel, a burst disk and 400 psi of air at above room temp, it's far from impossible.

What kind of damage can it do with a .12 gram?

I certainly wouldn't want to be hit by one, here's some 0.25 gram BB tests:


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0.25g BB at 1017 fps straight through a steel (empty!) lighter fluid can

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0.12g BB at the same can, only penetrated one side. Sadly the chrony didn't get a reading.

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0.25g BB at 982 fps straight through a plastic toy container

very nice. how loud is it?

Actually not that loud, thanks to the approximately 1:1 chamber/barrel ratio and long barrel.

could you be getting incorrect results from having the chrono to close the the muzzle

That's the way this particular chrony is meant to be used, and as I've said I've compared it to other chronies at high velocities and got consistent results.

The reason that he couldn't break the sound barrier is because he is using room temperature air. Unheated air will not push a projectile past the speed of sound under normal circumstances.

Not so, commercially available air rifles like the Airforce Condor can break the sound barrier using unheated air and a hammer valve.

I don't think it is impossible to push a projectile pass the speed of sound with air pressure, it is just difficult. I will be trying it soon, and hopefully I can make it happen.

Those are some great videos Jack, but what happened to the sound?

No sound unfortunately, 3 digital cameras in this house and none of them have a microphone

I tried a Diabolo Baracuda extra heavy 31 grain 0.25 pellet (6.35 mm, needs to be rolled down a little to fit the barrel) and got 577 feet per second, an impressive 23 foot pounds

Sadly I still can't get a velocity reading for the 0.12 gram BB, the chrony keeps saying "bad"

Impressive energy figures for something so small. Considering how that stacks up at about 20% of the .22 LR round, I'm damn impressed.
Yeah, I know the .22 LR is pretty wimpy, but I still wouldn't want to get hit with it.

Any idea why the chrony is objecting to the .12g?

It's also not impossible to achieve supersonic air currents in a smooth enough barrel. If the pressure differential at the valve is high enough, and the projectile is really light, the supersonic air currents generated at the valve could continue down the barrel. And if your airflow is supersonic, you can get a projectile to go supersonic.

Has anyone ever tried drawing a vaccuum in the barrel to increase the initial pressure difference? A thin burst disk on the end would be used to seal it before the projectile hits.
A better question is, how much difference would it make?

(Oh, and nice Plinker from Hell)

You would of nailed mach 2 in Hybrid form (jokes).
Well done with those velocities, the lighter bb that the chrony can't read must be going super-sonic
Let us know when you get bored and turn it into a hybrid 8)
Nice work.

how are you using tape as a burst disk? can you demonstrate in any way?

Have you tried using PBA Raptor pellets? 25% increase in velocity