you referring to this https://www.umarexusa.com/new-for-2022-the-airjavelin-hpa-adapter-blogi havent heard much about results either./. My guess is most people are buying off the shelp 850 psi tanks , which yeild no gains so they never post it.. id go 1200 psi , and maybe swap out the hammer spring. the reality is , all the tanks sold are generally 850, 1800, or 2200 on the major sites.. And the sweet spot is likely 1100 to 1400..
It looks like it would take down some good sized game too. Looking forward to your review Paul.
Iremember watching a YT video where the guy extended the folding stock and showed a slanting "port" that allows you to insert a round tip hex. That should allow you to increase/decrease the hammer spring tension. Starts at about the 1:50 - ish minute mark