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Thread: Effective barrel length

  1. #1

    Effective barrel length

    I read this a question came up

    Barrels are only there to accelerate the ball from a standstill to 300 fps. In theory they also help with accuracy but that's another post. The ball goes through incredible acceleration on its way down the barrel. The balls acceleration rate is approx. 50,000 feet per second to get to 300 feet per second in 10 inches. The entire barrel travel time is about 6 thousandths of a second and this means the ball is seeing about 1500 G's when its getting pushed out the gun. Although this may sound incredible if someone out there would like to do the math you will see that I'm close.

    Air pressure behind the ball is what causes this acceleration to happen. This pressure varies between the different guns but is generally between 50 to 125 pounds per square inch at its peak. The air pressure peaks right when the ball starts moving down the barrel, after that, the ball moving down the barrel creates a bigger chamber so the pressure drops. This is why low pressure guns are a myth, in reality all guns shoot at considerably lower pressure than 200 psi.

    Peak pressures above 150 psi tends to break balls down the barrel due to really high acceleration and G forces. If you don't have any way to control the peak pressure behind the ball, the only way you can change it is to go with lower pressure in the air chamber, hence low pressure guns. AGD uses the precise contour of the power tube tip to release air in a controlled manner behind the ball to limit peak pressures to around 60-80 psi..

    It is simple to understand that the harder you push something the faster it will accelerate and get up to speed in a shorter distance. So what distance do we have to get the ball up to speed? The effective length of the barrel is from the balls position before it's fired, to the place in the barrel where the pressure gets released, This is usually at the first porting holes or the step in the barrel. Porting is there to release gas pressure!! You are effectively stopping the acceleration at the ports so your 14" barrel that is half full of holes only has an effective length of 7".

    Now we understand that we need to limit the peak pressure behind the ball to keep it from blowing up, and that the pressure drops as the ball moves down the barrel. The next question we need to ask is, how far down the barrel does the ball have to go before the pressure gets to low to do anything useful? That answer is 8-10 inches. We know this from looking at the graphs that our gun dyno puts out. If your peak pressure is higher, say over 100 psi you can get away with a shorter barrel, if it's lower then you need a longer barrel. Since AGD is the only gun manufacturer to actually test their pressures behind the ball you might have a hard time getting this info for other guns.

    So as far as our guns are concerned, the best efficiency would be had with an 8-10" effective length barrel. Since two piece ported barrels with an effective length of about 5-6" are the rage right now you hear a lot of complaints about gas efficiency. Under some circumstances there is a good reason to use a short effective length barrel. Short barrels cut off the acceleration abruptly by venting and this has the effect of tightening up the shot to shot velocity variation. If you need this at the expense of efficiency then go ahead. Tighter velocity control usually translates into some improvement in accuracy due to better consistency.

    So if you want the best of all worlds, limit your peak pressure, let your ball accelerate all it wants, don't follow the crowd and keep asking questions.

    ---Tom Kaye

    And a question came up in my mind about this part.

    Porting is there to release gas pressure!! You are effectively stopping the acceleration at the ports so your 14" barrel that is half full of holes only has an effective length of 7".
    I was thinking of getting a 18in Freak barrel. Since the freak barrel has some porting what is the effective length of that barrel. In other words is there a good reason to get a 18in freak?

  2. #2
    Join Date
    Oct 2002
    Marion, IN

    Re: Effective barrel length

    Originally posted by rakshasagenn
    . In other words is there a good reason to get a 18in freak?
    Feedback from: AO,PBN

  3. #3
    Join Date
    Jul 2002
    Pissin on your steps, Shelton, CT
    i dont like long barrels, hence the 8 inch barrel i own.

  4. #4
    Join Date
    Oct 2002
    Marion, IN
    Ok a little more info. I just measured some freak tips for ya. A 14" has 4 1/2" tip and a 16" has a 5 1/2" tip, that makes me guess that an 18" tip would have 6 1/2" worth of porting, just a guess tho! I don't notice much of a diff. between 10-14".

  5. #5
    Join Date
    Jan 2002
    Halifax, N.S., Canada
    The longer barrel helps in sighting down the barrel and that is all.
    Except for the Automag in front, its usually the man behind the equipment that counts.

  6. #6
    Join Date
    Dec 2001
    Silicon Valley, Ca
    You can use it as a lance for jousting later on.

    "When you get married, you learn really quick that there's a good time, and a not so good time, to start playin' snap-shooting-from-behind-the-couch moves with a brand new $1,000 paintball gun." -Jack & Coke

  7. #7

    will the ref at the tourney allow that?
    DO they have paintball jousting touneys were everyone brings their longest barrels and try to stab each other?

  8. #8
    Join Date
    Oct 2001
    Durham, NC
    well, a 18" barrel does have use, you can move Sup'Air bunkers around with it but thats about all...other than that...get a 10-12" freak, itll work just as well

  9. #9
    alright thanks

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