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 Post subject: .8:1 vs. 1.5:1?
 Post Posted: Fri Jul 11, 2003 9:00 am 
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Originaly posted by aire,
So I just want to make sure I have my math correct.
If I use a 4" x 12" combustion chamber, and a 2" barrel diameter, my barrel length would be:

32" at 1.5:1 ratio
60" at 0.8:1 ratio

So it seems like this .8 ratio will result in some pretty mondo barrels.
I guess this is the dilemma between convenience and performance?

Maybe I could do a 1.1 ratio as a compromise?


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 Post subject: or
 Post Posted: Fri Jul 11, 2003 10:00 am 
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Originaly posted by Freefall,
you could just use a smaller chamber


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 Post subject: your math is wrong
 Post Posted: Fri Jul 11, 2003 10:00 am 
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Originaly posted by Orangekid13,
if you go the other way, and find barrel volume and multiply by .8, it ends up giving you a chamber of 4"x24". For the 1.5, the math is right as far as i can tell. I think that the proper barrel length for a 12"x4" chamber at .8:1 is 30". I could be wrong, and if i am, please correct me, but not with ratcalc, cause that's messed up.

~Orangekid13


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 Post subject: I get ~38" for 0.8:1
 Post Posted: Fri Jul 11, 2003 12:00 pm 
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Originaly posted by jimmy,
chamber vol * 0.8 = barrel vol


(4/2)2*pi*12*0.8 = (2/2)2*pi*L (L= barrel length)


L = (4/2)2*pi*12*0.8 / (2/2)2*pi


L = 4*12*0.8 = 38.4"


But you should do the calc with the actual ID of the 4" and 2" pipe instead of the nominal IDs.



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 Post subject: in other words ...
 Post Posted: Fri Jul 11, 2003 1:00 pm 
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Originaly posted by aire,
When the two ratios are talked about, people say it incorrectly.

A C:B ratio of 1.5:1 could also be expressed as C*0.6667=B

So, when you say C*0.8=B, that is like a C:B ratio of 1.25:1

When people wrote about "0.8 ratio", I had thought they meant C*1.25=B ...

See where I was confused?

I now see that C should always be larger than B (which makes sense) ... anyway, thanks for helping me understand.


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 Post Posted: Fri Jul 11, 2003 4:00 pm 
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Originaly posted by andeh,


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 Post subject: oops .. i hosed it up
 Post Posted: Fri Jul 11, 2003 5:00 pm 
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Originaly posted by jimmy,
C:B ratio of 0.8 means (vol chamber)/(vol barrel) = 0.8


So the formulas are


chamber vol = 0.8 * barrel vol


(4/2)2*pi*12 = 0.8*(2/2)2*pi*L (L= barrel length)


L = (4/2)2*pi*12 / 0.8*(2/2)2*pi


L = 4*12/0.8 = 60"


(and aire was correct)


But you should do the calc with the actual ID of the 4" and 2" pipe instead of the nominal IDs.



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 Post subject: you dont HAVE to...
 Post Posted: Fri Jul 11, 2003 11:00 pm 
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Originaly posted by Orangekid13,
using the pipe size is close enough usually, there's not too big enough of a difference to count it unless you're testing like latke, or getting really exact.

whatever

~Orangekid13


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 Post Posted: Sun Jul 13, 2003 7:00 pm 
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Originaly posted by man_o_brass,
A proper 0.8:1 ratio will result in a long barrel with more volume than the chamber. But you HAVE to start your calculations from the chamber volume. If you start with a normal barrel and then match a chamber to it with a 0.8:1 ratio, the gun will be very underpowered. Read my theory page:

http://www.geocities.com/man_o_brass2/main_page.html

It should take care of the details.


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