Agreed Alistair. I've worked on 7 or 8 Sports and this was certainly the case. Except strangely enough for one, owned by the late Ed W, whose Sport I agreed to fettle as part of a deal (for a BSA no.8 sight I think it was).
The rifle had stubbornly refused to go above about 8 ft/lbs, much to Ed's distress. I tried a Maccari sping, a Maccari seal, a Maccari Arctic spring, FWB factory seal and spring, polishing the piston and cylinder, etc etc. I just couldn't get more power whatever I did and finally had to admit defeat!