I tried to introduce this about 20 years prior but the Internet wasn't ready for the concept.
Customers complained because the spring was super tight on their spring guide and back then to them it was the wrong spring.
Fast forward today and most now know or at least they can be directed on why this is a great FWB spring.
How to use this spring.
We have preset this spring for you to shorten it for an easier install.
Next take a file or Dremel tool and dress the inside of one end of the spring ID. that has the spur in the inside. That is where the wire winds tighter on the inside of the spring at the end of the shaved coil. Just carefully grind or file just the tip of the spur. Should take less than a half a minute. You are taking off the point only- maybe 10 thousands of an inch- just dressing it up and taking the point off of the wire. Don't make a mess and hog out the spring.
The spur end will be the biggest ID end of the spring so you will want to put this on the guide. The guide should have our moly paste on it and the spring will be twisted on which will yield much smoothness. And when you cock the gun the spring ID expands a bit anyway.
A very skilled airgun worker would also want to chamfer the OD of the spring guide as FWB didn't. No instructions will be given on this as you should be skilled before you attempt this although it isn't brain surgery.
Works great with our seals and moly paste ( sold separately)
*****You will want to put one of these on the spring guide ( trigger end) for more power and it reduces the chance of galling.