Stubber

Stubbers, or stub guns, are weapons from as early as M1, but mostly 20th century guns (our times) in the 41st millennium. Needless to say, most haven't aged very well when you consider how powerful everything else is. The only thing that they have going for them is they are cheap, they can still kill an unarmored humanoid target, and are durable as hell and depending on its mechanics and care, can be and have been in use SINCE M2. They are incredibly weak against much of the universe's people - in fact, they are the only thing that a Guardsman's paper armor will reliably stop. This should give you an indication of exactly how weak they are. But just remember - every dog has their day.

Variants

Stub Pistol

God made men, Sam Colt made them equal, and John Browning made them civilized. It's a basic pistol in two variants: the stub automatic which is like a 9mm handgun and the stub revolver which is, of course, a generic revolver. If you're in a gang on a hive world, it'll work pretty well because you're probably going to be shooting at other people without armor, or unarmored Arbites. Very reliable, unlikely to jam, manufacture is a breeze, and ammo is plentiful. However, if you're trying to shoot an Ork, even headshots might just bounce off his skull.

Stub Gun

Though not technically defined, these are basically Stub-type guns that are bigger than pistol-size and smaller than Heavy Stubbers. This category likely includes our semi/automatic rifles, submachine guns, and the like. Still basically mid 20th century firearms - think M-14s/16s, H&K G36, Uzis, Tec-9s and Mac-10s (as ghetto now as they were in our time), Stens, and the ever ubiquous AK-47/AKM and its derivatives... many of which are probably still working as good as new. It should be noted that this has been used as another name for the Autogun, and even if they aren't technically the same thing, both are very similar to each other.

Heavy Stubber

Well-known is the Heavy Stubber, a machine gun used as a vehicle mount in the Imperial Guard, because in 40,000+ years, humanity has still been unable to top the genius of John Browning's legendary M2 (who's surprised?). Just ask the goddamned Orks.

It is basically a Browning M2 .50 cal Heavy Machine Gun. Hell, a few are probably still working since the ancient days. Unlike the smaller Stub guns, Heavy Stubbers actually contain enough mass to do similar damage to a Bolter round, and will reliably blow people's limbs off now as easy as they did then. Unlike the others which have been phased out, these are still in the mainline army arsenals, and are often pintle-mounted on vehicles or used in Heavy Weapon Squads in the Imperial Guard. Especially so for vehicles produced from worlds that do not have the resources to produce Heavy Bolters, or those who just find it more economical to push out a hundred Heavy Stubbers for what it would take to make one Heavy Bolter in the same time. Obviously, they are not as strong as the Heavy Bolter they replace, which is several times more powerful than a regular Bolter, but they are stilled damned powerful enough, and they DO GET SHIT DONE