A clank gun (or machine cannon) is, simply, a projectile weapon used by a clank soldier-unit; specifically, what a Wulfenbach clank wields. It's set apart from "normal" gunnery by its size and power. Theoretically this weapon can only be lifted, positioned and fired by a clank built to handle the weight and recoil of such a weapon. As such, units wielding it possess both the mobility of (heavy) infantry and the firepower of (light) artillery. It appears to be a single-barrel autocannon weapon enveloped in a barrel jacket.
It is not possible to determine at this time how the ammunition is fed into the clank gun's chamber; when the clank soldiers use them, there is a possibility it might be fed from a storage chamber in the clank's casing rather than a cartridge installed on the gun.
Use by non-clanksEdit
As you can see from the demonstration below, a single clank gun is awkward for even three Jägerkin to handle...and the recoil is rather more than a human-sized leverage can compensate. However, Jäger generals, with their significantly larger size and strength, may be able to handle a clank gun. 
Given that even the Jägers have difficulty wielding, let alone using a clank gun, it is indeed remarkable that Baron Klaus Wulfenbach carried - and continuously fired - such a weapon without assistance.[note 1]
- ↑ Though the weapon carried by Baron Wulfenbach was not identified as a clank gun, it is identical to the one utilized by the Jägerkin (see above), down to the same firing sound. Additionally, the Baron is a gigantic man possessed of great strength, making his use of a clank gun more believable.