Ork guns should basically all be Borderlands guns: "Reverse Recoil" that increases accuracy the longer you shoot, rebounding bullets, recoil patterns (dis gun shoots in a skull formation 'cause it's extra killy!), and other wacky stuff that works because the Orks believe it works.
Dis is what id expect to see from some flash gits rolling around and id love to do this myself! silly humans don't even know how much DAKKA and ork can bring!
If an Ork believes enough that it can shoot, it can shoot. If an Ork believes enough that red bullets shoot faster, they shoot faster. If an Ork believes that somehow his gun can jam, it will jam.
This is true, but what Ork would believe in something as silly as a jam? Jamming interrupts the dakka. No good shoota is ever gonna interrupt the dakka.
Orks that get told that guns sometimes Jam. And they then think their shootas can jam. Which would in turn make the shootas jam.