Let me share some technical details:
Piston ID: 21.25mm
Guide ID: 12.93mm
Allowable Solid height of spring: 96.28 mm (I will discuss Solid height and allowable solid height in another post)
Considering the Spring guide ID, a supplier of mine has sent me a spring whose spec is as follows:
Wire ID: 3.048mm
Coil ID : 13.43
Number of Coil: 31.5 and almost 10 inch long
Seems to be a good fit for the spring ID and very easy to cock the gun.
I was trying to insert it inside the gun…and oops…very hard. I could not do it by hand. Like most GAMO’s, the B40 has almost nil preload length and you don’t need a spring compressor to dismantle the gun. The spring was hard because the spring was not set. So I decided to SET the spring by using a spring compressor.
This is what I did. I inserted the spring in a tube and then inserted a rod almost the same size as spring ID behind the spring and put them under compression, in solid height state for almost an hour.
The picture below shows the spring under compression.
Once the spring was removed from compressor chamber, I found the spring reduced by 20%. This is absolutely normal!! If you do not preset and try to inset the spring directly in to the gun, there is a high chance of accidents, and moreover greater chance of structural defect of the spring. Therefore “setting” spring is very important and has to be done very carefully.
After setting the spring, I found it is very easy to assemble the gun. Once assembled, I found the gun to be very easy to cock and very less recoil. And power??? Yes the power has increased.
The picture below shows the impact.
Yes, that’s true; the pellet is IN a wall made of solid concrete. BAM!!!