Consider the little RWS "Manders" silencer.

Only about 2.5 / 3 inches long, very light, just use a male-male UNF adapter and you're away <img src="http://jsramsbottom.co.uk/bbs/e/icon_smile.gif" alt="Smile" width="15" height="15"><!--graemlin:-->

Ditto Bob's "soundbiter".