[MaciekA]

The rating of a spring is just a rating of a spring... A lot of things can happen in your cylinder (ports? lack of seal?), along your piston rails (slowing down the piston with friction?), behind your cylinder head (sorbo stealing volume?), along your nozzle (crap seal?), in your hop chamber (crap seal?), and in your barrel (too short?)... that can reduce your output velocity.