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GAMO Bigcat Airgun Tuning

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.  

Fixing scope rail

If you have purchased scope-rail from here http://target-tune.in/international/products/IHP-scope-mount.html then follow this DYI

This is all what you need Yes screw and drill machine is not shown here. Just follow the picture.

Place the rail (the side marked in red) as shown in the picture:

for 4mm Tap you need 3.2mm drill

Once done, dismantle (You can use the following link) the gun.  File off and wash out  unnecessary material. Assemble them back. Once done, use the screw to fix the rail, check if you can cock. If not remove the screw which is located towards the back sight file off a little (say 1mm) and screw it back. You should be able to cock now.

Reason to change Spring guide for HW30

This is what you usually cannot see with naked eyes.

In the picture below, you see on the original (OEM) spring guide hof HW30 showing some bucking.

The reason is very simple. The OEM spring guide is way below the required OD size for the spring.

Secondly, the Material that used for the guide is not strong enough to hold the power of the spring.

This picture shows the custom made spring guide.

No bucking observed. Alignment of the tophat is not inline with the guide thus the little difference you see down there.

How to remove rust

This is what I am going to restore.

Rusted object

Rusted Object Anothe view

Now going to Add Cooking salt 1 spoon in a mug filled with water so much so that the object submerged it fully. Then I add equal amount of vinegar. Mix it well and the put the object.

Salt

Vinegar

submerged in water

Keep it for 1 hr. and then remove it and then wipe it off with a wet cloth. See the result..

Rust is removed

Rust removed

Understanding airrifle Barrel.

A rifled barrel means a few helical grooves around a hole.  Usually the grooves are all in even numbers viz. (4, 6, 8, 10, 12 etc).

The diameter of the head of a pellet is usually the same diameter as that of the groove, and the diameter of the pellet skirt about .2mm more. This allows the pellet to sit firmly on the breech and its travel path through the helical groves gives it a twist in it’s axis which in turn gives stability while traveling a long distance.  Continue reading →