I play in a youth orchestra and so they`ve loaned me an A Clarinet to use for the year. The problem is that the barrel is too big for my mouth piece so it wobbles around and if I try to use the barrel from my Bb it doesn`t fit on the clarinet properally and sends the tuning all wonky. Any suggestions that don`t envolve buying a different mouthpiece would be appreciated.

foam padding around mouth piece cork probably would work.