Shoulder Cannon-Well, “torso cannon” is sort of the default for any major weapons used in powered armor (since only a few species have, well, hands).  Most suits of powered armor have two or three independently articulated mounts, usually mounting rifle-caliber weapons and/or light support weapons such as grenade launchers or rocket launchers.  There’s usually an ammo feed to a central ammo supply on the user’s body, and they always mount sensors on the weapons so they can be safely poked around corners and fired around hard cover.

This doesn’t count for heavy weapons, which are usually carried by one of any number of drones that can provide support and be expended as needed.