Hatsan 60S with shortened barrel (obviously pictured without silencer):
SMK XS19 with shortened barrel:
5 shots from the SMK at 25 metres - I draw a small dot with a Sharpie to aim at, and the 5p is for scale (I used to love shooting this one in front of people who loudly proclaimed Chinese guns as being junk )
Both guns benefited massively from the WW kits, but the Hatsan by far enjoyed the most noticeable change. The SMK was smooth and sedate from the off, while the Hatsan was a grinding pig and took the most work of any gun that I've tuned to date to get shooting nicely. Predictably, once I was happy with it, I sold it
I'm not agreeing or disagreeing with the longer spring theory - by and large a longer, lazier spring will produce a less lively shot cycle and can generate more power. This is how the FWB Sport took the world by storm in the power stakes and left everyone else, Weihrauch included, for dust. They basically used a longer spring with a softer action out of narrower gauge wire. Obviously that's a gross oversimplification and there's a lot more to it than that, but changing the spring might do the trick.
I've had instances where a Titan number 2 in an HW80 was downright nasty while another Titan number 2 (same number of coils, diameter of wire, overall length, inside and outside diameter) resulted in a sweet shooting gun.
Anyhoo, good luck - Will is a gent in every sense and he will get you where you need to be. Keep us posted