EXPECTED POWER: 14.5 Ft/Lbs OR 19.65 Joules
Once I have received the Gamo Bigcat, I checked the muzzle energy of the gun immediately. It was giving 13.3 fpe with CP 7.9g Not bad!!The shooting experience however not so pleasing. Twanging and unpleasant vibration. Being a very lightweight airgun, the vibration actually transferring to my hand. So decided if I can do something. I striped it down.
It is very natural to see a Bend spring from GAMO like this. And next the seal
One may choose to change the seal.
As we all know Piston is the Heart of the Powerplant.
The better the piston =Better the gun shoot
So lets have a look at the piston.
So the progressive bulged. All piston of gamo has this problem. And I don’t know the reason why the spring has to be exposed so much.
The more the spring exposed the more sound it will create while shooting and also while cocking and de-cocking.
I noticed the OD of the piston also bulged. have a look.
So the end of the piston looks better? Wobbling is guaranteed and a definite impact on SD. Therefore accuracy will be compromised.
Lets see what else we can spot.
Not BAD. 2.5mm gap. While it will be cocked, think in a slow motion. The spring guide getting pushed forward and the spring that is inside of the piston will buckling heavily like this: 
Which will create, harsh, twangy airgun. It will reduce the power and spring life. Spring will bend, crack.
I just did a small thing to change the GAMO characteristic entirely.
I CHANGED the Piston!!.
I took this piston http://target-tune.in/international/products/GAMO-High-Speed-Piston.html
The OD for TTI Piston is 24.85mm is an excellent sliding fit for 25mm GAMO. No Wobbling so better shot consistency thus the accuracy.
The ID of TTI piston is carefully made so while cocking the spring will enter inside the piston very smoothly. As you see the piston ID smaller than GAMO OEM piston for arresting bucking for better axial force and longer spring life. It also eliminates unessential twang.
Natural Spring Guide. You don’t have to but any extra spring guide. Your existing spring guide should do the magic with this piston,
After the piston installed, look at the compressed spring. There are still gap between coil to coil even though see how straight the spring is. More interestingly, you will be noticing immediately the smoothness while cocking and a solid piston smashing sound while firing. You will feel like you are shooting an expensive gun. As I told before the GAMO characteristic entirely changed after this.
I have got a 911 fps with crosman premier 7.9gr with TTI’s GAMO FULL POWER SPRING and that makes 14.5 fpe with a undoubtedly shooting pleasure.
Targettune's Weblog 
Sounds good to me,I have a stoeger x20 and Gamo magnum .22..
But very informative read it all.
I think, both can use this piston.
will it work on a gamo silent cat
Certainly!
Very nice piston.The Gamo has virtually the same fitting parts as the Stoeger XS10 / 20 Perfecta55 SMK XS18-19 Crosman Shadow / Phantom and also many of the KRAL rifles. These are very good value for money pistons that I will soon be using.
do you have a nitro kit converter for gamo silent cat spring piston
Hi Jack, not yet but we are going to introduce soon the nitro parts.
Can you also make spring guide for later model Gamo, ( plastic spring guide) and how much it will cost
Not at this moment we are making but we have a plan to make any moment soon.
here we are http://target-tune.in/international/products/GAMO-Tune-kit-for-ATS-trigger.html
Do not go by this picture. We have done a little more modification after this pic is uploaded.
Hi
Will your metal trigger tuning kit and the piston you manufacture fir the Gamo CF20 ?
Cheers
Carl.
Yes
Hello, I am from Romania and I try to launch an order for a piston and spring but it is impossible to finalize my command. It is a problem with delivery in my country?
Thank you.
We deliver throughout most parts of the world. However, our key fulfillment person is sick at this moment. Hence we are not accepting any orders at present. We are process of getting alternative arrangement. Once the same is done, We will start taking order. Our sincere apologies for any inconvenience.
Hi Guys, Sorry to hear about your Sick employee/employer, I hope they are recovering well. Im just curious if you are taking orders again now? If not, all the best.
Thanks Steve, for your wishes. Our technical director Raymond is still sick – as you know recovery is slow when the disease is cancer. He has undergone Bone Marrow transplantation.
Thank you very much for supporting us during these challenging times. We are planning to announce resumption of business as usual activities, hopefully, soon in the future.
Regards,
Pamela Singh