When I'm not at work I'll see what I can find for that (my firewall blocks too many things for effective searches of that kind of thing!).

Basically it's a hook-shaped rammer that allows the rammer, sponger, etc. to be entirely behind the muzzle at all times.

Aboard ship it also has the advantage of not requiring the gun crew to lean over the rail (since most captains do NOT want the gun muzzle inboard of the rail at all, to protect the public aboard).