Okay guys many thanks for all your help. now stage two if i put a flugel mouthpiece in my cornet (thirty year old Getzen Capri which Getzen have confirmed is a Bb) it plays centered (ie the mouthpiece only just goes in and therefore makes the cornet that bit longer). However if i put my Bach cornet mouthpiece in (1&1/2 C) and pull the tuning slide out 25 mm ( one inch) it is in tune. The question is.. is 25 mm too long indicating that perhaps thirty years ago cornet mouthpieces were slightly different in length? Many thanks for all the previous replies.