potential velocity

[Tailgunner]

Are there any calculations/formulae available to determine POTENTIAL velocity out of a given barrel length/pressure/caliber.

For instance: if one were to introduce an initial pressure of 800psi to a piston in a tube (think bullet) of a caliber of .30 (3.14 x .30 x .30 = .282" squared).

In other words.......one would apply 800psi to an area of .282 square inches for a certain distance (barrel length) where the pressure would fall off (I think) as the bullet moved up the barrel and one would also have to take a friction coeficient into account.........what would happen????

The point being.........if I would want to build a gun that used CO2........and had a 30 cal barrel......... of 15" length.............I would need to supply CO2 at (about) 800PSI..........for a certain length of

time..........to an enclosed tube.............to a certain weight projectile........that encountered 'X' friction over the length of a 15" barrel...

are there any Rocket Surgeons out there........I'm making myself very confused.


any help is greatly appreciated - Cheers - Gus

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AW CRAP wrong thread

[webstien]

lol, moved to general chat, no worries.

[Voltar1]

Are there any calculations/formulae available to determine POTENTIAL velocity out of a given barrel length/pressure/caliber.

For instance: if one were to introduce an initial pressure of 800psi to a piston in a tube (think bullet) of a caliber of .30 (3.14 x .30 x .30 = .282" squared).

In other words.......one would apply 800psi to an area of .282 square inches for a certain distance (barrel length) where the pressure would fall off (I think) as the bullet moved up the barrel and one would also have to take a friction coeficient into account.........what would happen????

The point being.........if I would want to build a gun that used CO2........and had a 30 cal barrel......... of 15" length.............I would need to supply CO2 at (about) 800PSI..........for a certain length of

time..........to an enclosed tube.............to a certain weight projectile........that encountered 'X' friction over the length of a 15" barrel...

are there any Rocket Surgeons out there........I'm making myself very confused.


any help is greatly appreciated - Cheers - Gus

\
AW CRAP wrong thread

Gus, how you been man, long time no hear
Walter here....

I got this somewhere and works pretty good.

(fps/172)^2=(AvePressure*BarrelLength*Caliber^2)/(Grains(0.025(AvePressure*BarrelLength*Caliber^2)))

Try that with ave pressure at approx half available pressure.
Your example with 115 grains gives 360fps
24" barrel gets you to 442fps

Walter

[jezX]

check what you are doing with the math , i don't think you are doing what you want . R square ? or D square ?
the friction is little in the barrel after the first 1/2'' . i think the way to determine this is by loss of psi for each shot ,compared to volumes in barrel. a larger surface area .30 cal compared to a .22 should go alot faster ,then calculate the difference in weight .

[thudthumper]

[(fps/172)^2=(AvePressure*BarrelLength*Caliber^2)/(Grains(0.025(AvePressure*BarrelLength*Caliber^2)))

did you derive that or find it somewhere? i'm curious to see the math behind it.

[cozmos]

its not the pressure itself thats deside the velocity, its the amount of gas, and how fast the weapon can transport the co2 to the barrel.

[sniper]

don't forget to include in the calculation the size of the port.

I can get potential velocity about 90 fps by just opening the port with all
and the pressure stays the same and another 100 fps from co2 to hpa.
140 fps with the combo + 24" barrel ......
we need probability assumption calculation formula ...... what if and only if.

[Voltar1]

check what you are doing with the math , i don't think you are doing what you want . R square ? or D square ?
the friction is little in the barrel after the first 1/2'' . i think the way to determine this is by loss of psi for each shot ,compared to volumes in barrel. a larger surface area .30 cal compared to a .22 should go alot faster ,then calculate the difference in weight .

Did you try the formula? If so what did you get? If not, why not?
Comes very close to actual results and is useful when scheming and doing 'what-if' calcs. Which is what Gus wants to do.
BTW I do not recall where I found that formula but sure appreciate it.
Walter...

[jezX]

voltar ..... i ment for the orignal post to check math . (rennuliat)
i assume his idea is different then your formula .
i didn't check your formula , i think i have seen it before . i'm more of a hard fact person not a formula person . of corse most stuff i build is based on some math . i may try your fomula see what i get

[millerlight]

try here http://www1.iwvisp.com/thehalls/ggdt/

its ment for pneumatic cannons, but may also work for airguns.