The .820 OD spring actually installed easily in the new HW95 piston with liner that I recently installed in my "Franken9". The spring with the supplied spring guide, top hat, and steel thrust washer installed with almost no preload (about 1/2" of preload). Personally, I do like the low preload requirement. After assembly the gun cocked surprisingly smooth and the latch-up at the end of the cocking stroke was positive with secure safety functioning. The cocking stroke SEEMED similar to a factory setup, berhaps a bit harder but not excessive.
A few CPLs over the chrony sensors showed 935-945fps using a Vortek VAC seal on the piston! I pulled the piston and installed a factory R9 seal and the chrony showed CPLs flying at 890-900fps.
As expected, this spring kit with the sloppiest fitting guides I've seen gave the most horrendous shot cycle I've ever experienced with a springer! Along with the excessively loud TWANNNGGGGG was the duration of that twang!! By the way.....the caution on the package states "WARNING NOTE, FITTING THIS SPRING MAY TAKE YOUR RIFLE OVER 12ft/lbs".....LOL, this warning certainly applies to MY R9! Perhaps there should ALSO be a warning tthat "NOISE LEVELS MAY EXCEED SHOOTER COMFORT LEVELS" LOL
This spring kit would be hopelessly over sprung if I were to use my standard home turned oring sealed piston cap arrangement so this spring kit will go into the "parts bin", perhaps to revisit in the future. Perhaps this spring with a fitted guide and top hat would shine when shooting heavy pellets, but my experience in the past is that once the fpe of a R9 weight gun exceeds 15fpe it becomes too hold sensitive for ME. I don't imply "less accurate", just that it becomes difficult for ME to shoot as accurately.
I've learned through the years that my R9s tuned to shoot CPLs at around 880-900fps will do everything I require of a springer out to 55 yards, so I'm not very inclined to "suffer the slings and arrows" of harsh shooting springers that give "braggin' velocities" but no practical benefits for my airgunning interests.
MOST Euro springer shooters must be DEAF to spring noise judging by how noisy this spring kit is considering that the sales pitch on the package states "Of the 100,000 plus 'OX' sold around the world, it is almost unknown for one to fail".....and......"Spring powered airguns sold in the UK outsell pneumatic, pre-charged, or gas ram systems by probably 250-1" etc. Pretty strong "sales pitch" to my thinking!! I'm sure that tightly fitting guides could muffle the twang/vibration, but I'm thinking that it would take an exceptionally tight guide to quiet such a strong spring, sooooooo.....this 'OX' spring kit gets a "thumbs down" for MY purposes!!! I didn't take the time to accuracy test the arrangement due to the fact that such excessive and long lasting vibration couldn't be good for my new scope! LOL