Heavy automatic cannons built from alien technology, too many teef, or usually both. Deffguns are heavy Ork weapons, fine examples of the Mek's craft that are made from all kinds of materials, mainly scavenged heavy weaponry of other races. Deffguns are so large they must be mounted on a special firing rig strapped to to an Ork's broad shoulders. No man could hope to fit into a Deffgun's rig without heavy augmetics or thick slabs of vat-grown muscle. This cumbersome rig is needed to absorb bone-breaking recoil each time the Deffgun is fired.
These provide most of the Ork's (heavy) ranged firepower, and deafen the wielder and anyone nearby. These guns buck, spark, spin and flash like no other, and are the second-deadliest infantry-portable Ork weapon. They are Imperial Autocannons in function, and sometimes in fact, but with random rate of fire because of ORKY influences.
Two known variants (or rather classification groups) of Deffgun are the Shooty Deffgun, which has an extremely high rate of fire and is mainly used against infantry; and the Beamy Deffgun, an energy weapon often made from a scavenged lascannon and very effective against armored target, although countless other variants like Plasma Deffgun are also known to exist. Deffguns are mainly used in battle by Lootas, who can gather enough heavy weapons so that Meks can make it for them, but they can also be mounted on Ork Warkoptas. The damage done by both can be very high and they are the epitome of dakka. For example, each shooty deffgun can do 12 damage a turn with six shots dealing 2 damage each, for each loota, in a squad. This gun is for when you need MOAR DAKKA