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Thread: Shorter barrel, does it mean that the rifle will be louder? Pcp specific.

  1. #1
    REP: Xhariep Jagters Colesberg

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    Default Shorter barrel, does it mean that the rifle will be louder? Pcp specific.

    I fitted a longer barrel from a 4.5mm Gamo CFX(memory loss) on my PP700 pcp pistol and a laminated stock to convert it to a "carbine".
    I had to thread the barrel around 40mm from the crown and now the barrel screws a lot deeper into the silencer than the normal rifle. The Gamo barrel had the plastic front sight which I removed obviously. The "carbine" is a lot louder than with the standard 5.5mm standard pistol barrel. Sound like you are popping a plastic bag, even with JSB Heavies. Am thinking of pulling a sleeve over the front barrel to bring it up to standard size and then thread it again. I'm a bit scared of just cutting the barrel to where its a uniform diameter, dont want to lose the "choke" the standard rifle have.

    I build rifle silencers from steel for hunting rifles on a weekly basis almost but ain't so sure about airrifle silencers as there is a lot less pressure and no flame involved.

    Any advice or opinions?
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  2. #2
    Sharp Shooter

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    Speculating......
    You've changed a 5.5 pistol to a 4.5 carbine without retuning the plenum volume, hammer spring tension or transfer port so multiple effects come into play.
    The caliber change : generally one needs more air (and maybe less pressure) to move a 5.5 compared to a 4.5. It's likely that your action, set up for 5.5, is pushing the lighter 4.5 pellet a lot faster.
    Barrel length change : If enough air is released a longer barrel will allow the pellet to accelerate to a higher speed.
    Silencer geometry : fitting the barrel deeper into the silencer reduces the internal volume and places the source of noise closer to the outlet. Sound attenuation will likely be reduced because there is less expansion volume and the air must therefore pass through faster. The silencer is sized for a 5.5 but now using a 4.5 pellet. Maybe this also allows more sound to get out past any internal baffles.

    So I reckon the higher pellet speed and changes to the silencer are causing more of a bark.
    Difficult to say what mod will be most effective but I would first use a chrony to check the pellet is not going supersonic and then restore the silencer to original geometry if possible.

    Sourcing a transfer port from a 4.5mm version of the same pistol might also help.
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  3. #3
    Sharp Shooter

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    Quote Originally Posted by wildeboer View Post
    I fitted a longer barrel from a 4.5mm Gamo CFX(memory loss) on my PP700 pcp pistol and a laminated stock to convert it to a "carbine".
    I had to thread the barrel around 40mm from the crown and now the barrel screws a lot deeper into the silencer than the normal rifle. The Gamo barrel had the plastic front sight which I removed obviously. The "carbine" is a lot louder than with the standard 5.5mm standard pistol barrel. Sound like you are popping a plastic bag, even with JSB Heavies. Am thinking of pulling a sleeve over the front barrel to bring it up to standard size and then thread it again. I'm a bit scared of just cutting the barrel to where its a uniform diameter, dont want to lose the "choke" the standard rifle have.

    I build rifle silencers from steel for hunting rifles on a weekly basis almost but ain't so sure about airrifle silencers as there is a lot less pressure and no flame involved.

    Any advice or opinions?
    Looking purely at the title of your thread. Yes, a shorter barrel will always be louder with the same power. Just compare the sound of a .22lr rifle to a .22lr pistol using the same ammo. It's a huge difference in sound.
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  4. #4
    Sharp Shooter
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    Ek het een van jou dempers, jy kan gerus maar een monteer op jou pcp hulle werk mooi. ;-)
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  5. #5
    REP: Xhariep Jagters Colesberg

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    Seems I will have to dust the chrony off and go test the little bugger, it packs a punch with the AA Heavies. Did a few unmentionables and was quite impressed....
    No ports on the PP700, but adjustable via a screw on the loading port.
    My thoughts on the smaller volume in the silencer also with the barrel screwing in so deep, maybe a new one from alum - reflex type as I don't want to lengthen the rifle as its a lekker compact size at this stage. Maybe a shorter, bigger diameter suppressor can do the job.

    Dankie DSF, ek het agter gekom dat die staal dempers n metaal-klank afgee op pcp's. Sal egter probeer met alum, ek het op n staduim alum dempers probeer vir jaggewere maar dit doen nie die ding vir my nie. Skroefdraad pak te vinnig op met carbon ens
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  6. #6
    Sharp Shooter
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    Jip, kry ook daai metaal stemvurk effek maar dit pla nie te veel nie.
    My oorlede pa het vir my dempers gebou soos joune out Alu vir die pcp's en met die dikker wande van die ligter materiaal raak jy ontslae van die stemvurk effek. Maak n paar en stuur hulle vir my ek sal hulle toets vir jou. ;-)
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