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AutoCocker Low Pressure PDF Print E-mail
Written by Joe Rieger   
Thursday, 13 November 2008 03:08
Tech: Go Low Pressure (Why and How)

There is much raving going around about guns that run at ultra low pressure.  You can hear of people running their guns on like 190 psi at 280 fps.  You can hear people boasting that they have the best accuracy on the planet because of low pressure.  You can also hear them say that they never break a ball thanks to those wonderful LP (Low Pressure from here on out) parts.  But what is low pressure?  Why should you go low pressure?  Why shouldn't you go LP?  This tech article explores these questions and more.

The first question you would ask if you're new to cockers is "What is LP?"  Well, low pressure is exactly what it sounds like, using a high volume of low pressure gas to fire a paintball.  If you have a slight background in physics, there are three basic laws that define how gas acts under a certain temperature, pressure, and in a given volume.  The formula is

Volume=(Temp. of Gas)/(Pressure of Gas)

This also applies to the gas used to propel a paintball.  We can assume for the most part that the temperature of whatever gas we're using is constant.  Using the aformentioned formula, if we increase the volume of gas, the pressure of the gas has to go down to keep that temperature a constant number.  This is the concept of low pressure, to use a larger volume of low pressure gas to propel the paintball supposedly more gently than with normal pressures.

One misconception I think is that people think Autocockers aren't low pressure as a stock gun.  However, if you understand that the 2k and newer Autocockers shoot at about 350-400 psi & 280+ fps out of the box, and you consider that most open bolt blowbacks use around 800 psi (approximate Co2 tank pressure) most Autocockers are low pressure anyhow.  However, people seem to have a need to shoot the lowest possible pressure.

Why should you go lp?  The real thing you should be concerned about is how to get better efficiency out of your gun and gas setup.  You can shoot an autococker at the 200 psi range and at field limits, but you're only gonna get one hopper out of a 68/4500 psi nitro tank.  Going low pressure with an Autococker means precisely controlling how much air is used for recocking the gun and how much is used to fire the paintball.  There are two basic ideas for going low pressure.

The first idea is to just throw in the lightest valve spring and a heavier main spring, allowing the valve to stay open as long as possible and use as much gas as it can.  If you're just interested in having lp then you could use this.  However, it's horribly inefficient since it has to use so much gas.  You should be concerned moreso about getting better efficiency out of your cocker and getting a lower pressure as a side effect.  The second theory, which is more efficient I believe, is to use all high flow parts (ie hi-flow bolt, valve, regualtor, etc.) with a stiff valve spring and a softer main spring, and let all the hi-flow parts lower your pressure for you.  This allows a useful volume to flow and at a decent pressure.  This utilizes the best possible efficiency from those $200 worth of parts you bought.

To go lp, you really don't need more than 2 new springs and a valve removal tool.  Despite what this page used to say, the stock autcocker parts are just as good as 95% of the aftermarket internals.  You can do just fine with the stock valve and bolt, both are actually rather efficient.  The hammer doesn't need to be changed unless you would like to pinch balls, which will be explained in a minute.  The stock cocker regs are adjustable, but they're just a pain to do, I'd recommend replacing the regs if you have the cash or will.  So then, first object is to get a nice pair of matched valve and hammer springs.  Your valve spring should be slightly heavier than your hammer spring, so that the valve isn't being forced to stay open longer than needed.  Try either medium valve and med-light hammer or med-light valve and light hammer.  If you're not sure what springs to get I've heard good things about the matchings of the springs from FreeFlow.  Just get the whole spring set.  Nelson spring kits are also excellent and probably cheaper. For instructions on how to do this next part, go to the teardown page.  Remove your valve and replace the valve spring, put everything back together, screw your velocity adjuster in only about 1-2 turns, and sweetspot your primary reg (Instructions here).  Next, properly set your pneumatic pressure (instructions on same page as primary reg).  If you're shooting right at where you want to be, fine, you're done.  If you're shooting a bit hot, back out the velocity adjuster a turn or so.  If you're too low, go in a turn or 2 or 3.  If you're way too low, try a different spring combination, namely a lighter valve spring.  If you're too high, use a lighter hammer spring.  You're gun should now be set to be most air efficient.  As well as being efficient, if you have a light enough hammer spring, your pneumatic pressure should be low enough that if a ball is only partly fed, your bolt won't close all the way on it, just stop on it, effectively "pinching" paint.

If the above procedure doesn't work for you, then fine, try it with the softest valve and hardest mainspring, or just go back to stock setup.  The nice part about having an Autococker is that you can really reverse most of the stuff you change.  I hope this guide has helped.
Last Updated on Tuesday, 02 December 2008 20:04
 
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