How long a barrel before pellet starts to decelerate?
- Thread starter Peep
- Start date
I think he wanted to know how long of a barrel to get maximum velocity without barrel being too long so that frictional losses come into play. There’s a lot of variables involved.I have wandered this a lot my self.
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Does seem to be what he was asking. There must be a maximum acceleration length for any particular powerplant and caliber but it would seem to be different for every combination.
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It’s dependent on valve dwell…how long the valve stays open. If the valve keeps dispensing CO2 (or air) for a long time, it will continue to accelerate the pellet through an ever increasingly longer barrel. As a practical matter, it isn’t something you need to be concerned about. With most OEM CO2 airguns, the problem is usually at the complete opposite end of the spectrum…far too much dwell causing it to waste CO2.
Only if you are making extensive modifications is it likely to become a consideration. For example, installing a valve with a pressure-assisted closing cycle (e.g. Cobra valve).
Only if you are making extensive modifications is it likely to become a consideration. For example, installing a valve with a pressure-assisted closing cycle (e.g. Cobra valve).
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Jim Giles of Crooked Barn fame recommended max 14.5" bbl for stock gun. My collection of CB's . +1 on what Nervous trig said. 
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Hi neroustrig, I want to cut the barrel back 5" so I can add a suppressor with out exceeding the stock length. Plan to lighten the hammer and spring to work more efficiently with the short barrel. What kind of fps do you think I'll get?
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For the most part with a stock gun with an 18 to 20 inch barrel you will loose 10-15fps per inch. For shorter barrels in the 14 or less inch range you will loose more. If your valve is modified for more power you will loose more velocity.
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It's going to depend on a lot of things. Go to www.scribd.com and look for The Airgun From Trigger to Target by Gerald Cardew. He has a great discussion on barrel length. Some of the factors include the transfer port, the barrel breech opening radius, the type of rifling, and many others. I joined Scribd just to get that one book. They have more airgun books too.
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That the first one I thought of when I saw the thread title! But Cardew's classic book is exclusively for spring-piston, not CO2 guns.
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This may partially answer your question: https://hardairmagazine.com/ham-columns/pcp-airgun-internal-ballistics/
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Cardew's book is focused on spring pistons. But much is applicable to CO2 and PCP. For example, his discussion of porting, barrel design, pellet design, and the basic considerations of energy management. I point people to Cardew's book every chance I get.
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