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Author Topic: Gamo CFR transfer port enlargement  (Read 334 times))

Offline James340

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Gamo CFR transfer port enlargement
« on: May 07, 2022, 12:03:13 AM »
I have a CFR . velocity is low.I have tried new springs ect ... anyone enlarged the transfer port? it's accurate but slow.I was curious.thanks for your time
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Offline Roadworthy

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Re: Gamo CFR transfer port enlargement
« Reply #1 on: May 07, 2022, 12:06:25 PM »
You do not indicate the caliber of the gun, the weight of your pellets,  the current velocity, or your expected velocity.  You can certainly enlarge the transfer port and doing so MAY result in a velocity increase.  If you go too far you will experience a reduction in velocity.  You do not mention which spring you are trying for a velocity increase nor what you have done with piston seal sizing if anything.  Have you checked your breech seal?  There are several avenues to explore before modifying the transfer port.  That operation can be really hard to reverse if you go too far.
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Offline James340

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Re: Gamo CFR transfer port enlargement
« Reply #2 on: May 07, 2022, 03:15:42 PM »
650 fps w/8.3 grain rws Superdome.all seals/o rings are new.piston seal is snug not a free fall fit."custom air seal"gas ram replaced the spring.
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Offline Novagun

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Re: Gamo CFR transfer port enlargement
« Reply #3 on: May 07, 2022, 09:50:44 PM »
I have just tested three CFX/CFR rifles all using JSB  .177 pellets at 8.44 GNS.
The rifle holding a Custom Airseals ram clocked 757 fps. The one with the standard CFR ram clocked756 fps and the one with a lower powered Challenger ram clocked 690 fps.
I don't know if this helps much as all have shortened barrels and have modified piston to use Weihrach piston seals.  I cant give any numbers from months or years ago because I have only just bought a chronograph.

I wonder if the rams lose a bit of pressure over time.
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Offline James340

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Re: Gamo CFR transfer port enlargement
« Reply #4 on: May 08, 2022, 12:02:53 PM »
I have just tested three CFX/CFR rifles all using JSB  .177 pellets at 8.44 GNS.
The rifle holding a Custom Airseals ram clocked 757 fps. The one with the standard CFR ram clocked756 fps and the one with a lower powered Challenger ram clocked 690 fps.
I don't know if this helps much as all have shortened barrels and have modified piston to use Weihrach piston seals.  I cant give any numbers from months or years ago because I have only just bought a chronograph.

I wonder if the rams lose a bit of pressure over time.
I want a little more fps.rifle is accurate so I will probably just leave it alone.I have had the igr for a year and it's been consistent
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Offline OleTomCat

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Re: Gamo CFR transfer port enlargement
« Reply #5 on: May 11, 2022, 11:20:56 PM »
I wouldn't mess with the transfer port.  I usually get about 700 fps our of .22 CFR/CFX yours should be shooting much faster than that, I would suspect that the seals in the rotary breach are not holding pressure.
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Offline Novagun

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Re: Gamo CFR transfer port enlargement
« Reply #6 on: May 14, 2022, 05:10:12 PM »
I recall there was an article or two in the Bristish magazine _ Airgun world    Somebody called Jim did some experimenting with various port sizes.  it affects or interacts with springpower and piston weights and can really mess things up  up.  He threaded the port so he could screw in various sizes.
Quite an undertaking for an amateur.
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Offline Airnut

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Re: Gamo CFR transfer port enlargement
« Reply #7 on: May 14, 2022, 07:54:56 PM »
Leave the transfer port alone messing with it usualy turns out bad. Don't Ask me how I know!
Sounds like your piston seal is a little tight.
No big deal. Either resize it or just shoot the snot out of it. It should loosen up after a few hundred shots.
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Offline James340

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Re: Gamo CFR transfer port enlargement
« Reply #8 on: May 18, 2022, 06:29:30 PM »
Leave the transfer port alone messing with it usualy turns out bad. Don't Ask me how I know!
Sounds like your piston seal is a little tight.
No big deal. Either resize it or just shoot the snot out of it. It should loosen up after a few hundred shots.
Frank
I resized it&lost velocity so went to snug.
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Offline Airnut

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Re: Gamo CFR transfer port enlargement
« Reply #9 on: May 19, 2022, 05:30:31 AM »
Sometimes it does not take much to go from snug to loose.
What chrono are you using and at what distance?
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Offline James340

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Re: Gamo CFR transfer port enlargement
« Reply #10 on: May 28, 2022, 01:55:18 PM »
Sometimes it does not take much to go from snug to loose.
What chrono are you using and at what distance?
crony f1 & point blank.I am getting 700 fps with 8.3 gr Superdome pellet.The o ring on the breach is leaking some.blows tissue off .I tried a looser piston seal but actually lost 50 fps so went with back to the snug fit
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Offline OleTomCat

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Re: Gamo CFR transfer port enlargement
« Reply #11 on: May 30, 2022, 10:24:18 PM »
Sometimes it does not take much to go from snug to loose.
What chrono are you using and at what distance?
crony f1 & point blank.I am getting 700 fps with 8.3 gr Superdome pellet.The o ring on the breach is leaking some.blows tissue off .I tried a looser piston seal but actually lost 50 fps so went with back to the snug fit

This is the kit you need, make sure you debur the tube up to the rotating breach, do not do any sanding or polishing where the breach rotates or you won't be able to get it sealed up..

You will have to pull the rotating breach plug all the way out to replace he O-ring around the outside, make sure you lube the tube all they way up and under where the rotating breach sits or you will damage the O-Ring installing it.

https://www.customairseals.com/product/gamo-cfx-cfr-royal-rotary-breech-seal/
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