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How Does Barrel Length Affect Power?

Discussion in 'Technical' started by Josh K, Aug 16, 2019.

  1. Josh K

    Josh K Self proclaimed AGF luckiest member

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    Firstly this is not a post about how to increase power on a rifle.

    I was looking through threads earlier when I started reading about another members Crosman 2250 and that he had put a 22 inch barrel on it. Someone else urged caution about it potentially increasing the ft lb above the legal limit.

    Why does increasing the barrel length increase the power? I assumed that the propellant ( co2 in this case) along with the mechanics of the gun itself dictated the power? What is the physics etc behind it?
     
  2. Popgun

    Popgun Donator

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    the propellant ( air ) is behind the pellet for longer, unlike a bullet where the propellant is expended in a predetermined distance within the barrel
     
    Josh K likes this.
  3. John Harrigan

    John Harrigan Verified Dinosaur

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    Succinct
     
  4. Josh K

    Josh K Self proclaimed AGF luckiest member

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    That makes sense! Thank you.
     
  5. Cinimod

    Cinimod Busy Member

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    I think it's all to do with amount of time that the Co2 has to build up its max pressure in an enclosed space i.e the barrel. As soon as the pellet exits, no more push behind and that's it at it's max power.
    That's why crosman can use the same mechanical bits it's the length that ups the power plus a few other self tune things that can be done.
    There does become a point that the co2 will expand no more and then friction takes over with the pellet still in the barrel and starts to slow. I think if memory serve me will that for a crocs an rifle 18" is best length and taking an inch off at a time decreased power in a specific time. I'll see if I can find it.........dom
     
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  6. Josh K

    Josh K Self proclaimed AGF luckiest member

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    Very useful to know. Using those principles, I'm assuming that a silencer doesn't add to the power due to the internal design with baffles etc as there is room for the air to expand inside?
     
  7. Cinimod

    Cinimod Busy Member

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    It's also to do with the initial working pressure of the gun. A pcp runs at high pressure so delivers a sharp force to the pellet which can accelerate the pellet more quickly whereas co2 runs at lower pressure so needs the enclosed length of barrel to help build up pressure, a bit more 'torquey'......dom
     
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  8. Cinimod

    Cinimod Busy Member

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    Correct, as soon as the skirt of the pellet leaves the crown no more power will be transferred.....dom
     
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  9. robs5230

    robs5230 леший

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    In PCP and C02 the propellant is still expanding when the pellet exits the barrel. Power continues to develop whilst that expansion is still taking place.
    I'm unaware of a co2 or PCP rifle that has a barrel that long, that air or co2 stops expanding before pellet exits.
     
  10. Cinimod

    Cinimod Busy Member

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    Also, especially with co2, temp will also add to the equation........dom
     
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  11. Cinimod

    Cinimod Busy Member

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  12. Jay Butts

    Jay Butts Donator

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  13. Simonix

    Simonix Engaging Member

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    I had a SMK CP2 pistol/carbine kit.

    As soon as you fitted the longer barrel in the kit, it upped the power from just under 6ft/lbs, to about 8-9ft/lbs.

    Clever these Chinese..... ;-)
     
    Rincewind666 likes this.
  14. short-carabine

    short-carabine Engaging Member

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    18" best for 2250s- IIRC some guy on the Crosman Owners Forum did a series of tests showing minimal gain beyond that. Hmm the Pyramidair link contradicts that!!
     
    Last edited: Aug 16, 2019
  15. ped

    ped Posting Addict

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    Carls data was on a pumper where he cut down a 24" barrel an 1" at a time and recorded the data
    Tom Gaylords article that 18" is the optimum length is incorrect also for co2 as provided you can supply the co2 the longer barrel will give more fps
    you do start getting into diminishing returns eventually
    I do have a copy of the pumper data and this will be comparable to a pcp
    I may still have the results of testing some std valves versus tuned valves using 3 length barrels -14.5" - 18" - 24" using co2 and regulated air @ 850psi using a powerlet eliminator so a small plenum
    to test the co2 I used a fresh co2 for each barrel and valve type- I'm told Tom used the same cart for his testing the barrels and by the time he got to the long barrel he was low on co2 and got the results he did
    one thing to note is 2250's with barrels longer than 14.5" look pretty silly especially when a silencer is added
     
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  16. short-carabine

    short-carabine Engaging Member

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    Looks like the article I read was flawed then, Ped.:oops: I upgraded my 2250 to an 18" barrel this year which yielded more FPS...as you say lobbing a really long barrel on a 2250 does look a bit silly. Mine doesn't look too bad with a slightly longer barrel and a mod on the end. Like to keep my Ratty portable and pointable!
     
    Jay Butts likes this.
  17. pjgtech

    pjgtech Bah Humbug.......

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    Yep, longer barrel = more power.
    My SMK Victory CP2 puts out less than 6ft/lb in its pistol format, eg: shorter barrel and puts out about 8ft/lb in its carbine format, eg: longer barrel.
     
  18. Lev Levvin

    Lev Levvin Pro Poster

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    Interesting...

    Is this also why amazon tribesmen’s really long blowpipes are so effective ?

    I’ve often wondered how a little native guy can get the puff to drive a poisoned dart a few inches long into a monkeys hide way up in a tree canopy

    A decent PCP would struggle !
     
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  19. hmangphilly

    hmangphilly Busy Member

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    If i were an amazon monkey ......

    I'd be keeping an eye out for a native guy with a big puff.
     
    Lev Levvin likes this.
  20. TopDog

    TopDog Well-Known Member

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    Hi all

    Just stumbled across this on one of my all too infrequent trawls and it reminded me of some work I did a while ago, albeit with springer test rifles.

    I think it generally bears out the notions mentioned so far and also may add some more food for thought!

    The report is available as a PDF at;

    http://freepdfhosting.com/9c935e9e65.pdf

    Hope you enjoy it! May even start looking at some of these issues again sin ce it's been a while!

    Happy Airgunning.

    atvb
    David
     
    John Harrigan likes this.

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