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Old April 23rd, 2008, 08:23   #54
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Originally Posted by Bontic View Post
I think this may be stickied somewhere I remember reading, but just wanted to check. This is true up to a limit, right? Beyond a certain length of barrel, the volume of the barrel gets close to the volume of the cylinder stroke. Then the "suction effect" will reduce fps - the backpressure runs out before the bb has exited. The air rushing down the barrel has expanded to its normal atmospheric volume, so will not expand anymore. Now the exiting bb has to "pull" on the air behind it, creating a lower pressure behind it than the pressure in front. The bb is decelerated again before exiting and fps drops. Presumably there is an optimum barrel length for every cylinder/piston, where speed is at its maximum.
Yes Bontic I should have probably qualified that but I thought it was evident. Once you hit the end of your accelerate (ie: positively pressurized air) if it is still in the barrel, friction will begin to decelerate your BB, and the recycling piston will suck air into the barrel, further decelerating the BB. So it is critical that your bore size on your cylinder has enough volume to push the BB to the crown of the barrel.
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