I went surfing with some serious intent yesterday, and turned up this book:
"Treatise on Ordnance and Naval Gunnery" by Lieut. Edward Simpson. First printed in 1861, it was used as a text-book at the U.S. Naval Academy until 1868. The drawings of a 4-truck carriage used in this book are identical to the carriage shown in this thread.
"166. Breast Piece. The inner part of the breast piece slides into a mortice in the brackets in front of the transom ; the height of its position in the carriage equals that of the lower sill of the port. The outer part hinges on the inner part. When the outer part is turned up, the carriage can be run out so as to have its fore trucks resting against the waterways, while the breasts of the brackets rest against the spirketting; by this means the weight of the gun and carriage is not allowed to concentrate on any one point of the side, a consideration of much importance when the guns are secured for sea, and the ship rolling heavily; when the outer part of the breast-piece is down, the fore trucks are brought well inboard, clear of the waterways, and the arc which the breast piece then presents to the spirketting enables the gun to be trained laterally, which is impossible when the gun is run out with the breast piece up."
Adrian, the drawings of this state of the art (soon to be phased out), 4-truck wooden carriage certainly do seem to display all the bells and whistles.
"167. Bed and Quoin. The bed and quoin are arranged to produce all the elevation and depression that the port admits; and, to prevent the quoin from flying out under the shock of firing, it is furnished with an iron projection on the bottom, which catches in the ratchett secured to the bed. The bed is kept in its place by being keyed to the bed bolt, as under fire it tends to fly forward. The inner end of the bed is supported by the stool, which rests on the rear axle-tree."