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Copper chamber question

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Copper chamber question

Unread postAuthor: us sniper » Mon Feb 18, 2008 6:32 pm

How long of a 1 inch chamber do you think I need for a piston gun firing a 7 mm metal ball through a 3' 1/2'' foot barrel? The chamber is type L copper with a 1 inch tee for the piston.
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Unread postAuthor: Ragnarok » Mon Feb 18, 2008 6:35 pm

No more than a foot I would say, and even that might be huge overkill.
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Unread postAuthor: SpudFarm » Mon Feb 18, 2008 6:52 pm

it depends on your barrel size.
are you going to use a bigger barrel an wad it up or do you have a barrel that fits you ammo?
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Unread postAuthor: Ragnarok » Mon Feb 18, 2008 7:02 pm

spudfarm wrote:it depends on your barrel size.

I assumed it to be around the 7mm that the ammo will be.
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Unread postAuthor: Velocity » Mon Feb 18, 2008 8:06 pm

If your chamber length was 5", that would be pretty good performance wise, and it would not be too wasteful (chamber to barrel ratio would be 1.5:1).
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Unread postAuthor: Hotwired » Mon Feb 18, 2008 8:12 pm

1.5:1 is an odd CB ratio that seems to appear fairly often...

I know I've got it but I wasn't following a ratio intentionally.
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Unread postAuthor: Ragnarok » Mon Feb 18, 2008 8:33 pm

Hotwired wrote:I know I've got it but I wasn't following a ratio intentionally.

Same here. HEAL's 120 cm barrel gives a ratio of about 1.5:1.

It was originally a case of the longest chamber I could neatly fit under a 100 cm barrel, then I decided to switch up to 125cm (later got trimmed back by 2" to reduce the frequency of me nearly bashing it on things) for a little more power, and that created the infamous ratio.

Not the most efficent ratio, but not too extreme in either direction.
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Unread postAuthor: Velocity » Mon Feb 18, 2008 10:11 pm

Most people think that 4:1 and above gives you the most power for pneumatics... while a 4:1 ratio will give you more power than a 2:1 ratio for the same barrel, it still annoys me, all that wasted air.

I usually go for 2:1... somewhat inefficient, but its all good. In my opinion, anything 2:1 and below is fine for a pneumatic. I think Jimmy 101 calculated that the ideal ratio (most efficient) for a pneumatic was like 0.2:1... but still, efficiency in pneumatic isn't quite as important.

OK, none of that might have made sense, but thats OK because I am tired.

/rambling and incorrect statements and things that inexcusable in the eyes of God
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Unread postAuthor: Gippeto » Mon Feb 18, 2008 11:49 pm

Wow, you guys like to sweat don't you! :lol:

After crunching numbers for the co-ax I'm building, I came up with a c:b of 0.613:1 (this is the smallest that still gave the performance I am looking for)

With your 7mm barrel and 1" chamber diameter, this works out to roughly 1 7/8" chamber length.
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