I had been disappointed with accuracy of the T-tempest in comparison with my senior - caused by very varied power, so full strip and noticed how extremely stiff the piston/seal was. On examination saw leading edge of seal had I assumed been chamfered very rough, I assume to enable it to enter the bore. Anyway, progressively emeried the seal till it was a smooth fit, then lubed (a touch of Nicks bumslide) & reassembled. Cocking much smoother, firing felt 'nicer' (and quieter!?), with consistent power (3.8 with JSB RS) and finally within my limited shooting powers has at last become reliably accurate - where before was a shotgun spread.