The gun carriage was developed by Gribeauval as early as 1748 and was copied by at least the Austrians.
While the Artillerie Gardes Cotes manned coastal fortifications and batteries, the naval artillery manned those that protected harbors and naval bases.
The gun tubes were the same that were used for siege artillery, so they were cast with brass and not iron, as the navy used iron aboard ship and in some shore installations.
Brass/bronze was 'sturdier' than iron, as iron had a tendency to fail catastrophically with the smaller calibers.
The pieces were as accurate as any others used by other belligerents, and were cast solid and then bored out for uniformity of caliber, windage, and ensuring that the bore was centered on the gun tube. They were usually either 16- or 24-pounders, both pieces having good range to reach their targets. Ships usually didn't do too well against permanent fortifications. And the fortresses would also have ovens to heat hot shot (red bullets).
The model does not have a traversing bar (handspike) on the rear of the carriage. The wood portruding at the rear is part of the slide for the recoil of the piece.
The second picture does have a handspike at the rear for traversing as the gun carriage has small wheels at the rear to allow for traversing the piece. The front of the carriage would be 'pinned' to allow it to traverse.
