[Bb] Centre of Gravity, ha ha. No, mine isn't the start, end or middle of anything. Or the second. Or even "a letter in the word 'open'".
[Blob] I said not when I said "No-one's got mine yet".

[MF] Too direct a clue there, Martha ! ;-)
Quick joky one : çontrol mechanism (6,6)

BTW, there is a definition for "Bust down reason" - it's not just a device. I can't tell if there is for "Case bust", which could just mean something that encases a bust ie. "Playtex Brassiere", which is wrong.

[MF] No. Slightly more amusing in a schoolboy humour sort of way.

[Blob] I think brassière would be clued as "Bust up reason (9)". [MF] "Case bust" wasn't meant to be a clue.