The subject today is the Experimental Nail Propulsion Mechanism, usually shortened to XNP4, and colloquially known as the Spike Cannon.
It is in its prototype stage, but after the Type Five Forward Engineer Incident (where it was employed by said improperly programmed android to great effect), it will probably be either pushed into large scale production or scrapped.
It resembles a cross between an oversized sleeve cuff and a rotary cannon, and has nearly no barrel besides the cartridge chambers themselves, which are rifled. Because of this, accuracy is somewhat limited at medium and long ranges.
The cartridges are 25x1.5 cm cylinders, roughly a third of which is high explosive and the rest of which is a high tensile steel spike, causing great difficulty in suppressing the recoil, and earlier models showed a serious risk of broken or dislocated arms.
Its stated purpose was nailing armor plates to each other for rapid fortification deployment and repair, although the offensive uses are obvious.