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My C:B is it correct?

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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My C:B is it correct?

Unread postAuthor: CannonBall » Mon Jul 23, 2007 3:27 pm

Hi my hybrid chamber has a volume of 535 ml my barrel is 2 meters long 22mm wide.. radius is 11mm
Chamber cubic inches = 32.64
Barrel1 cubic inches 22mm wide = 38.34
Barrel2 cubic inches 28mm wide = 75.15

How i calculate what my chamber to barrel ratio is?
and should i stick with my 22mm barrel or get a 28 mm>?
For the 28 mm 2 meter long the volume is
1231.50 ml = 75.1507409 cubic inch

I am asking this because i think my hybrid is under its max performace it makes alot of damage and noice with flames out of the barrel.
But i think it can do better

I shoot my hybrid at 5x or 6 x

Thanks :lol:
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Unread postAuthor: boilingleadbath » Mon Jul 23, 2007 3:44 pm

You divide your CHAMBER volume by your BARREL volume.
I suggest you get a flame-resistant suit, because there are alot of people around here who really don't like it when... slow people build and use hybrids.


Anyways, this means that your barrels give you C:B ratios of .86:1 and .44:1.

Which means that both of the barrels are smaller than they could be, and that the larger barrel (28mm) will give you higher muzzle enerergies. (in most cases)
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Unread postAuthor: CannonBall » Mon Jul 23, 2007 3:55 pm

Yes thanks i found out the calculation..
But one question

A bit hard to explain im not so good in english..\
ehmm let's say
my barrel stays the same lenght but the volume increases wy would the muzzle velocitie go up?
if i would use a 1 meter barrel bit a C:B 0f 0.2/1 the muzzle velocitie wouldn't be high because of the barrel is short... correct?

So can i conclude?
That if i extend my barrel to something like 4/5 meter to a c:b of 0.2/1
i would increase my muzzle velocitie much more.. than getting a more wide and short barrel?
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Unread postAuthor: Pilgrimman » Mon Jul 23, 2007 5:31 pm

The projectile accelerates until the friction from the barrel starts to decelerate it. The ratio is determined by how much impetus is behind the projectile, and at what point the gas expands enought to the point that the impetus no longer overcomes the effects of friction, and the friction decelerates the projectile. I've heard of cases in low-powered combustions where the projectile is actually sucked down back in the barrel when the gas behind it cools!

To all smart people: make corrections to my post as needed. I'm not 100% sure on everything I said, but I think it's right.
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Unread postAuthor: boilingleadbath » Mon Jul 23, 2007 8:58 pm

Your are correct that a larger diameter barrel will give you a higher muzzle energy. (under the fast-combustion model, assuming the flow isn't choked)

There are two ways to look at this:
1) The larger barrel has more cross-sectional area, so there is more force on the back of the projectile... more force times the same distance equals more energy.

2) The larger-volumed barrel allows more efficient energy transfer due to less residual pressure at the end of the shot. Higher efficiency times the same energy input (same chamber) equals more muzzle energy.
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