This double-length rifle uses a pair of trunnions to mount its barrel into a swiveling mechanism fastened to a lightweight, two-wheeled carriage.
It takes a full-round action to set up the carriage. The carriage has a hind leg, allowing the wielder to wheel the device about and immediately prop it for stability during combat. Unlike other two-handed firearms, you must fire the double hackbut while it is mounted, or else firing it imparts a –4 penalty on attack rolls and the recoil knocks the wielder prone. A Large or larger creature can fire a double hackbut one size smaller than it is without its mounting as a normal two-handed weapon and without the danger of being knocked prone, but takes the normal penalty for firing an inappropriately sized weapon.