Results of said Rapax spring testing!
So firstly let me pre-requisite, yes I know my J are a little warm for the UK, this will be resolved once the new barrel goes in along with a longer airbrake to bring them back under control. The gun is stored without a spring so no it's not a firearm sitting there. My testing 0.2's are a mixed bag, it does look like there was an inconsistency.
All shots fired on a 20" Sport with FAST hop set for 0.43s on it's last outing with SBA 60° bucking and a SBA airbrake piston head with medium brake inserted.
Silverback M150 using 0.2 in fps
470
475.9
476.1
437.5
475
Silverback M150 using 0.43 in fps
348.4
347.9
347.5
346
345.6
Rapax 2J using 0.2 in fps
479.9
476.9
477.2
441.7
476.5
Rapax 2J using 0.43 in fps
345.7
345.4
347.8
348.3
350.1
Other points to mention
So in a one after the other test I was wrong with my previous statement, the Rapax does feel a bit easier to pull than the SBA M150.
The Silverback spring has had 2 game days (read 1000) bolt pulls so is likely better bedded in than the brand new Rapax.
There was no spring twang!