gun carriage

lavetti A metal frame on which a piece of ordnance is mounted for firing or transportation.
(RQ:RJfrs AmtrPqr)

But then I had the massive flintlock by me for protection. ¶(..)The linen-press and a chest on the top of it formed, however, a very good gun-carriage; and, thus mounted, aim could be taken out of the window at the old mare feeding in the meadow below by the brook, and a 'bead' could be drawn upon Molly, the dairymaid, kissing the fogger behind the hedge, little dreaming that the deadly tube was levelled at them.