Blowguns- .40 vs .625


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John79
August 2, 2010, 10:40 AM
I have owned both, and as expected, I progressed from .40 to .625. Now for hunting, (which I never did, due to the poor chance of a humane kill) I know the 625 is better in every way. But for accuracy and velocity, given the same length tube, which caliber has the upper hand? Having used both, I always got the feeling that the .40 pushed the dart faster.

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M-Cameron
August 2, 2010, 10:50 AM
ok, i really know nothing about blowguns...but that really shouldnt matter because its all pretty simple physics (usually)...

given both lengths are the same, you will theoretically get a higher pressure with the smaller caliber, which should translate into increased velocity......as for accuracy i really cant say, but given the .40 will have a higher velocity it should also have a flatter trajectory, which could lead to an increase in accuracy.

so if speed and accuracy is what you want, i would probably choose the .40

John79
August 9, 2010, 01:42 PM
Kinda what I gathered as well. Anyone experience this 1st hand?

RyanM
August 9, 2010, 05:42 PM
Actually, pressure will be the exact same in both tubes. The only way to increase the amount of pressure is to blow harder. Ever used a compressor at all? If it's set to 100 PSI, then it outputs 100 PSI, no matter what size lines you use.

That means that the .625 caliber one will have 2.44 times as much surface area, and 2.44 times as much force behind the dart. However, the square cube law says that if the darts are scaled up in every way, the .625 darts will be 3.81 times as heavy as the .40 ones. 2.44 times as much force on a dart 3.81 times as heavy, means a slower dart (but one with more energy and momentum).

M-Cameron
August 9, 2010, 06:54 PM
Actually, pressure will be the exact same in both tubes. The only way to increase the amount of pressure is to blow harder. Ever used a compressor at all? If it's set to 100 PSI, then it outputs 100 PSI, no matter what size lines you use.

thats because the compressor works harder to keep the pressure equal in larger lines.....

according to boyles law..(P1)(V1) = (P2)(v2)
P1 = pressure of your breath, im going to assume its constant for the purpose of this explanation

V1 = volume of your lungs, also a constant

P2 = the pressure in the blowgun

V2 = the volume of the blowgun

assuming both blowguns are 36 inches in length....

the .40 would have a volume of 4.5 cubic inches...

the .625 would have a volume of 11 cubic inches.....


for the .40

C = p2 (4.5)

thus P2 = C/4.5


and for the .624

C = P2 (11)

thus P2 = C/11

since the .40 has a smaller volume, it will theoretically have a higher pressure than the .625 given the the lung volume and breath pressure dont change.

RyanM
August 10, 2010, 07:00 PM
since the .40 has a smaller volume, it will theoretically have a higher pressure than the .625 given the the lung volume and breath pressure dont change.

You understand that pressure in the lungs doesn't change, but somehow think that pressure in the pipe changes? That's really not how compressed air, or any other fluid, works. Pressure in the lungs is exactly equal to pressure in the tube, no matter what size it is, unless it's larger than the lung capacity.

The pressure will only increase if you exhale through a valve, turn off the valve, then use a compressor or piston to re-compress the air you just breathed out. And the valve is necessary, otherwise the pressure would go back into your lungs. Boyle's law really doesn't work the way you think it does.

http://en.wikipedia.org/wiki/File:Boyles_Law_animated.gif

John79
August 13, 2010, 08:42 PM
Please don't let this degrade into a debate about your personal interpritation of physics. I just wanted to know if anyone aside from myself had experienced an increase in speed of the dart from .40 to .625

Joe Demko
August 13, 2010, 08:46 PM
None of the arguing about physics matters. This is exactly like archery hunting. The wounding mechanism is cutting/pierceing/bleeding. Speed and projectile weight only come into play with respect to trajectory. Increased kinetic energy is a complete non-issue.

boomer1911a1
August 13, 2010, 09:07 PM
John 79: Absolutely!
I've owned both, and I could push the .40 noticably faster than the .625. But due to the extra mass, the Sixty-two packs more wallop. (This sounds like the new 9mm vs .45 debate!) :)

ChaoSS
August 13, 2010, 11:52 PM
Ryan, I am afraid you are wrong.

Pressure, if given a chance, will equalize, however, as the projectile moves down the tube the fluid dynamics becomes very complicated, in fact, high powered air cannons often are found to work just as well as lower pressures because the air simply doesn't move fast enough for 100 psi to create any more pressure once the projectile starts moving than, say, 25.

RyanM
August 14, 2010, 01:11 AM
Ryan, I am afraid you are wrong.

Pressure, if given a chance, will equalize, however, as the projectile moves down the tube the fluid dynamics becomes very complicated, in fact, high powered air cannons often are found to work just as well as lower pressures because the air simply doesn't move fast enough for 100 psi to create any more pressure once the projectile starts moving than, say, 25.

Go weigh some darts, then check back in. .625 caliber darts actually do weigh more than 2.44 times as much as the .40 caliber ones, especially if you're comparing "hunting" quality ones. 2.44 times as much force on more than 2.44 times as much weight, means a slower dart with more force.

The lungs are only capable of 5 or 10 PSI, but several gallons of volume. In the context of airguns, that does mean continuous pressure for any reasonable caliber airgun. Human lungs are nothing like a precharged airgun. They're really more like CO2, which is fixed at about 800 PSI, until the cartridge runs low.

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Please don't let this degrade into a debate about your personal interpritation of physics.

Okay, this statement is exactly what's wrong with the education system these days. There is no personal interpretation of physics. Physics work the way they work. Air works the way it works. And it's a very simple fact that you cannot blow 5 PSIg into any bizarre shape of magical tube, and somehow end up with more than 5 PSIg anywhere in the system. If the public education system had done its job properly, you would know that a magical "force multiplier" like that would literally allow for a first-order perpetual motion machine, which draws infinite energy out of the aether.

John79
August 19, 2010, 08:11 PM
Ryan, someone else read up on physics, and interpreted what they read or learned in a different, and admittedly flawed manner. That is still their interpretation of what they read about physics. Just as you can misinterpret a foreign language, and you (your interpretation) is incorrect, that is still your interpretation nonetheless. (:

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