jipi2084@hotmail.com wrote:Thanks so can you help me ?

Chamber : 4'' X 18'' = 226 ci.

my two first one were really not well made lol

volume chamber = PiR<sup>2</sup>L = (Pi)*22*18 = 226 ci

volume barrel = PiR<sup>2</sup>L = (Pi)*12*25 = 78.5 ci

CB = (chamber volume)/(barrel volume)

Rearrange the equation to;

(barrel volume) = (chamber volume)/(CB)

A reasonable CB is anything from about 0.6 to 1.0, we'll choose the oft quoted 0.8. You've already figured out that the chamber volume is 226 ci. Plug these number into the equation;

(226 ci)(0.80) = 180.8 ci

Use the formula for the volume of a cylinder;

(volume barrel) = Pi*r<sup>2</sup>L

Since we want find L (i.e., solve for L), rearrange the equation to;

L = (volume barrel)/(Pi*r<sup>2</sup>)

Plug in the values for the volume of the barrel (180.8 ci), and the barrel radius (1");

L = (180.80)/(Pi*1<sup>2</sup>) = 57.6 inches

So the barrel should be ~58 inches long. Going up or down ~15" inches in the barrel length won't make much difference in the gun's performance.

Always a good idea to make sure the units check out. Looking at the equation above in terms of

just the units;

L = (in<sup>3</sup>)/(in<sup>2</sup>) = inches

So the units are correct.

jipi2084@hotmail.com wrote:I read that your barrel should not be 1.5 time smaller than the chamber size like 4'' should not be plugged with smaller than 1.5'' barrel Is that true ?

Not really. There is really no safety issues with say a 1" barrel on a 4" chamber. There also really isn't any choke issues, the amount of choke is really just a function of the barrel diameter. A 1" barrel will have basically the the same degree of choke whtether it is attached to a 2"D or a 4"D chamber.

In general, combustions don't preform very well with barrel IDs of less than an inch or so. To get decent performance the barrel would have to be very long.