C: Harpoon Cannon. We don't need to worry about packing powder or running out of ammunition if the turret uses ballista mechanisms to fire chained harpoons and then reels them (and any catches) back in.
You create a torsion driven firing unit, known to the common man as ballista! The common man probably wouldn't think of firing a harpoon from one of these babies, and he won't need to since it will do it itself!
First step is making the wooden parts. Wood is somewhat annoying to work with as far as golems are concerned, as the mesh has to be applied on its outside of the wooden structure then covered with either a lacquer or plaster when you can't sandwich it between two separate pieces of wood. At least those are the traditional methods. With your current project it will be unlikely to take a beating, so you don't lose much from the outside method. Cross beam, cross bars, arms, frame, and so on and so forth are carefully carved out of the quality wood offered by your contact.
Next is the metal portion. Harpoons and chains. Golem mesh is highly heat resistant and can be added during the smelting process, making it easier to add to metal than wood. Not that his portion particularly needs it, but this will allow it to move around obstacles when being pulled back in and to detach from targets at will. You make three harpoons alongside three long chains.
Finally, the rope. As with the metal it is fairly easy to weave golem mesh in with your rope. It will let the golem control the tension of the firing unit a bit more, mostly to prevent catastrophic failures in the skein.
With all the parts made you get to construction, starting at the ground with a sturdy four-footed stool. You place the Animal core, a first sized bronze ball with a glowing red gem in its center, in the middle of the stool where it won't get away. You insure the swivel works and begin adding the mess to the woodwork, with the core disabled for safety. You build the ballista up from that position, continually connecting it to the golem core. It looks much like a standard ballista, though its "paintjob" would give it away as a self-driving weapon. This includes the crank, which allows the golem the same mechanical advantage as a human user. You then attach three harpoon mechanisms to the front underbelly, including the harpoon, the chain, and a second/third/forth crank for returning each harpoon. At least I think this is what the design calls for, I think "harpoons" is meant to be more than one rather than one big harpoon? The firing ark is designed so that it will shoot above previously fired chains, though there is a high chance of the second or third shot colliding with previous shot's harpoons and the Animal core isn't smart enough to avoid such impacts without direct human intervention. Before firing the harpoons are held on wooden platforms to the side, the golem tipping them into firing position when necessary.
With crossed fingers you turn on the Animal core and register yourself as its user with a drop of blood. It hops to life with a shudder. You test it against some hay bales in your Master's testing range. Movement is stable, the harpoon cannon is capable of turning 360 degrees without issue. It is capable of accurately picking a target and firing. Shots go slightly under 100 meters. You had hoped for more, but the chains add a significant amount of extra mass and end up making the projectile significantly heavier than competitors. Testing against some armor scraps, you find it is able to pierce standard armor at under 50 meters. Against heavy armor or things tougher than humans it won't be reliable at this distance, but it should be able to damage lesser threats reliably past it.
Overall all your hopes and fears are both realized. It is weaker than a black powder weapon of equivalent size, but it is fully capable of firing and reloading without issues (so long as the harpoon chains don't get tangled together in a way it can't reverse).
Are you happy with this as you masterpiece submission, or do you want to make modifications?