Possible Clues:

• Exhaust quietener
• Attachment to arm when bent, reclines
• One helps to hush up a report
• Mr Goodman, interrupting, cries out for muffler
• A car spares outlet may have one over a barrel!
• Because round leg not quite right, one's attached to arm
• One suppressing inconvenient report on firing?
• Keeps it quiet taking someone out for a few shots without making a racket
• A car spares shop may have one over a barrel!
• Takes away sound of what judge says in court, right?