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Thread: Gamo CFX after fettling

  1. #1
    Marksman

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    Default Gamo CFX after fettling

    Hi all

    Have put new spring from Gamo and new Gamo piston seal. New breech seals.

    i am only getting about 14.3 fpe with gamo pro magnum pellets 15.43 grain. have shot about 200 pellets through it. i was hoping for about 16fpe

    breech seals not leaking , (i actually took in and out several times to make sure was not getting nicked, all perfect) checked with talc powder around breech

    wonder if i should keep shooting to bed in more or put couple power washers on spring

    i did all the polishing and de burring etc and used moly paste 60% very very sparingly , actually burnished it into the piston and cylinder etc and made sure was non left in. basically is running dry but very slippery

    not sure why is lowish on power
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  2. #2
    Sharp Shooter
    WP HFT/Springer Champ '15

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    No where in your post do you talk about the accuracy
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  3. #3
    Marksman

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    its accurate, but i am wondering why is low on power compared to what is expected. am not going to get into debate about accuracy and power , i am well aware that accurate is good and springers shoot better at 12fpe etc etc.

    i am trying to understand why the power is low thats all. maybe an out of round cylinder , etc etc. am also trying to determine if i have right spring in it. they make spring for 12fpe and 16fpe. but when i ask about which spring i need..... i get the why do i want more power discussion instead of which spring it is. have asked Gamo direct for serial number of full power spring to make sure i have right one installed...no answer
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  4. #4
    REP: WS Airguns

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    Did you install the new spring as is? The shape you got it from supplier, or did you polished the ends? Did you check for coilbinding when the rifle is cocked?
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  5. #5
    Marksman

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    i polished ends and polished tophat etc. i bought spring from gamo dealer in Portugal, so i assume is the 16fpe version, but who knows. i may have 12fpe version and fettling is great or 16fpe version and something is wrong.

    spring coil binding , i havent checked, as i assumed would be ok from Gamo OEM dealer
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  6. #6
    Sharp Shooter

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    Hello,

    Your loss of perceived power could be because the seals in the rotary loading bit is leaking , this is not the small breech seal but the larger O-ring , these seals sometimes blow out.

    To replace these seals the complete rotary bit must be removed and replaced , it is a real swine of a job to do this.
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  7. #7
    Marksman

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    Quote Originally Posted by Juniper View Post
    Hello,

    Your loss of perceived power could be because the seals in the rotary loading bit is leaking , this is not the small breech seal but the larger O-ring , these seals sometimes blow out.

    To replace these seals the complete rotary bit must be removed and replaced , it is a real swine of a job to do this.
    see original post have replaced these breech seals and checked them for leaks. wonder if new piston seal is leaking
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  8. #8
    Sharp Shooter

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    Quote Originally Posted by busanga View Post
    see original post have replaced these breech seals and checked them for leaks. wonder if new piston seal is leaking
    ene

    There is also a small "neoprene" seal that seals between the barrel and breech block that could be leaking.
    Also check the tolerances between the rotary breech block and compression cylinder , I was forced to use oversized O-rings when doing mine and I still could not achieve a perfect seal.

    In my experience Gamo compression cylinder tolerances are REALLY sloppy , If all else fails you may have to have the compression cylinder honed and trued up , in my opinion this is not worth doing on this rifle.
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  9. #9
    Marksman

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    Quote Originally Posted by Juniper View Post
    ene

    There is also a small "neoprene" seal that seals between the barrel and breech block that could be leaking.
    Also check the tolerances between the rotary breech block and compression cylinder , I was forced to use oversized O-rings when doing mine and I still could not achieve a perfect seal.

    In my experience Gamo compression cylinder tolerances are REALLY sloppy , If all else fails you may have to have the compression cylinder honed and trued up , in my opinion this is not worth doing on this rifle.
    if you are talking about the seal on the front of the rotating breech block, i have changed that as well as the bigger O-ring on back of breech. it had crossed my mind on getting a slightly thicker O-ring i believe standard is 22 x 1.5mm

    what i really don´t understand about the rotating breech design is what pushes the front breech seal tight against barrel.
    when not cocked piston seal pushes against breech , hence you cant rotate it, but when cocked there is nothing pushing breech tight against barrel. so when you fire surely some air escapes before the air pressure pushes the breech enough to seal...
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  10. #10
    Sharp Shooter

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    According to your forum profile you own a Pro sport. So why spend time and efford on a Gamo CFX?
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  11. #11
    Marksman

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    Quote Originally Posted by Juan View Post
    According to your forum profile you own a Pro sport. So why spend time and efford on a Gamo CFX?
    because the prosport works perfectly already, no need to fettle it any more than it has been
    i also own an HW100 SK that works perfectly too and has had lots done to it
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  12. #12
    Cadet

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    The CFR is even worse than the CFX.
    Not sure you will get much more than the 14fpe you are getting unless you can re engineer the way that rotary breech locks in place.
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  13. #13
    Marksman

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    Quote Originally Posted by Sableman View Post
    The CFR is even worse than the CFX.
    Not sure you will get much more than the 14fpe you are getting unless you can re engineer the way that rotary breech locks in place.
    chap in Ireland claims was getting 18 fpe out of the CFX , i have my doubts, but 16fpe seems fairly common.

    am going to try thicker O ring on back of breech

    a way to engineer the rotating breech would be to have a threaded insert so when the breech was rotated closed the thread would pull the breech front seal tight against the barrel end.

    i believe some air pressure is lost because the rotating breech (RB) is not held tight against the barrel while the gun is cocked and when fired the air pressure pushes the RB against the barrel end, but some air must be lost before the pressure seals the front seal tight enough ??

    could even engineer a lip in the cylinder so the back of the RB is pulled onto the lip with an o ring seal... RB would be perfectly sealed then

    not that difficult to engineer really ..just a lip in the cylinder and either thread in front of breech into barrel or thread in lip so breech pulls into it.....
    Last edited by busanga; 06-02-18 at 22:35.
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