Upgrades for Star L85?

[Bazzerker]

Hello all,
New to upgrading but want to take small steps. What I want is better range and accuracy.

I was thinking of buying a tight bore barrel but what is best? 6.01, 6.02, 6.03? very confusing. At this time should i change the bucking and nub? the standard one is very good in design as it has a flat surface.

Also I am not sure if I should upgrade the motor and gear box parts? Should i look at changing the piston head and increase

I have tried a M100 spring but that threw the FPS upto 410-440. It current fires at 310.

any help would be appreciated.

thanks