Autogun
An Autogun is a chemically-powered projectile throwing weapon (a slug thrower, durr), that can be compared to late 20th to early 21st century fire arms, though it is (probably) slightly more powerful, which is why it avoids the title of Stubber (which have basically no improvements on World War II firearms) which are even worse than lasguns (there is not a single part of a suit of flak armor that a rifle sized Stubber can pierce at any range according to some sources, even though WWII Rifles were pretty powerful) Alternatively, since stubpistols are more powerful than autopistols, it's possible the difference has more to do with calibre and/or tech level. Simply put these weapons use a propellant to accelerate a metal projectile to punch holes in things. It is a significantly older weapon than the Lasgun, and does not see quite as much use due to the Departmento Munitorium. So if a young and often curious Guardsmen tries and ask his superiors, mostly a Commissar (Yes, reasonable Commissars do exist) on why a Lasgun is preferred over an Autogun by Imperial Standards, they will tell you a whole list of things such as the following...Lasgun Power Packs weigh significantly less than Autogun magazines and are far more sustainable (rechargeable via heat, light, or wall outlet), Lasguns are also significantly more accurate and require notably less maintenance than Autoguns, and have no recoil, meaning even the 8-year-old baby-faced kids and 98-year-old dusty seniors that has been recruited from the Imperial Guard can fire it straight. So a big reason that Autoguns were phased out was a matter of practicality, but there is one thing the Autogun has that the humble Lasgun doesn't, it is the amount of different types of ammunition you can carry, from Incendiary to AP rounds and even HE rounds that makes the Autogun a miniature Bolter. This means that while the Lasguns are used as the more common assault weapon, the vast variations of the different ammunition makes the Autogun a tactical weapon in some sense of form. Though /tg/ rather enjoys musing that the main reason was cost (all that grimdark spent ammunition came from somewhere, after all). In spite of the ammunition problem, the Autogun still sees use throughout the Imperium (particularly among PDF forces, as they do not have the overwhelmingly massive logistical issues the Imperial Guard does), and its removal from large parts of official service hasn't stopped its development. There is significant debate over the actual power of Auto and Stub weapons, with the "high power" team citing higher tech level and advanced materials, and "modern power" team citing no mention of any kind of recoil compensator (limiting power), and less innovative designs. Meaning some or even most autoguns may actually be be less advanced than modern firearms. After all our modern cannon rounds are definitely more advanced, and autoguns are meant to be built on all sorts of backwater worlds.
Tl;dr, if the Lasgun is called a 'Flashlight' then the Autogun is called a 'Stapler'.
Variants
Autopistol
Most often a machine pistol or submachine gun, the Autopistol is a single-handed submachine gun (called the Uzi Autopistol) which is frequently used by Chaos heretics (and on occasion, traitor guardsmen) and cultists who don't particularly care about accuracy or expenses and wish to be able to make noise and cause death at a close distance (the former is done better by an Autogun than a Lasgun) as they close in to use their swords. Quite fittingly, many of the autopistols manufactured by the Imperium are based off the MAC-10/MAC-11 weapon series.
Autogun
There are dozens of other Autogun models that have been created since, including more-advanced versions that use caseless ammunition. One common variety is an assault-rifle sized version formerly used by Imperial Guard regiments, known as the Armageddon-Pattern Autogun. It can fire on semi-automatic, 5-round bursts, or on full-auto and holds 60 rounds in a triple-stacked magazine. Most versions are modded to fire specifically in 5-round bursts, allowing it to achieve 12 bursts per mag. Whilst this Autogun is not hugely damaging, its fire rate is extremely high, allowing it to quite figuratively chew through body armor at medium range. Usually they carry 5-8.5mm bullets like in real-life, though higher than 8mm rounds are usually considered too slow (as in low velocity) or have too much kick to be practical for a typical assault or battle rifle. Buy hey with some models being 12 round slug-chuckers autoguns aren't known to always be practical, with some models firing rounds that have more in common with hand-cannon style rounds than rifle rounds. Autoguns are commonly employed by pirates, rebel groups, Chaos cultists, Kriegers, Planetary Defense Forces, Hive Gangers, Adeptus Arbites and low-tech civilisations that are too underdeveloped to create even a simple Lasgun, which puts into perspective just how poor these people are. (Hey, that includes us...)
In Warhammer 40,000: Fire Warrior, the Stormtroopers used by the Guard detachment on-planet uses Autoguns that have been given special armor-piercing rounds (read regular AP rounds) to improve their damage output, essentially putting them on-par with Hellguns. Paired with the weapon's fast fire rate, they're probably the earliest weapon you can reliably take down a Space Marine or Chaos Space Marine with, though clearly better options are available.
Autocannon
The Autocannon is the big-cheese of the Autogun family (and possibly related to the 88mm flack gun Bofors 40-57mm), firing enormous shells capable of tearing through bodies like a guillotine through a French aristocrat's neck. Most commonly mounted on vehicles, but also seeing use in Imperial Guard Heavy weapons teams, it possesses a worrying rate of fire, and good armour penetration, proving that even older tech can work when made sufficiently huge. It used to be much better, using what were approximately up-scaled Heavy Bolter shells to literally kill anything, but then Horus kicked a tantrum and the Mechanicus forgot how to read. You know, business as usual. Basically, these autocannon shells were to 40k's autocannon shells what Baneblade cannons are to battle cannons. Yeah. By the way most modern cannons actually use advanced shells like this, suck it imperium.
The standard Autocannon makes a satisfying POM-POM-POM sound as it chews up targets up to four feet away. It hits at S7AP4 and is a Heavy 2 weapon, making it statistically better than the Heavy Bolter against everything except Toughness 4 and less models. The long-barreled Hydra variation is used on the Hydra Flak Tank, and is designed to serve as anti-air support but used to chew up any cocky infantry that gets too close. Nowadays it gives warning shots that may clip an enemy if that enemy is standing right in front of it and jumps up and down screaming "SHOOT ME" (and even then might miss). Fortunately, it has an additional two feet of range, so while it only has one job, it tends to do it pretty well.
Then there is the Reaper variant, which only the Chaos Space Marines get because Assault Cannons were discovered after the Horus Heresy, and everybody Imperial promptly thought they were cooler than the Reaper Autocannon. This is an infantry-portable, twin-linked Autocannon that wants to put its shells in your face at 36" or less. Scary for light vehicles and monsters, the Imperials were right (for once) to switch to the Assault Cannon for infantry fighting. Fluff-wise it's mostly popular due to it's reliability and durability, capable to operate for years without repair and heavy maintenance, while also often being used as a heavy club in close combat - compare it to the rapier assault cannon, which needs it's barrels to be replaced after each battle or else they would jam or even explode.
Then at some point, the Traitor Legions and their Dark Mechanicus pals looked at the Reaper Autocannon and asked, "How can we make this even more rapey?" So they came up with the Helstorm Autocannon, which apparently can only be fitted to vehicles and aircraft such as the Hellblade due to its sheer rate of fire. It has the same profile as the Reaper except for firing an extra shot per attack and adding delicious Rending because fuck assault cannons. Now if only GW would let the forces of Chaos get their collective shit together and replace every vehicle mounted heavy bolter with S7 AP4 Heavy 3, Twin-linked, Rending.
Also because Chaos likes to add daemons to things, and daemons make things goofy, Chaos Space Marines have access to another vehicle-mounted variant, the Hades Autocannon, which bafflingly can only be mounted onto a dinobot (probably because it's propelled by warp-flame or something). Fieled onto a Heldrake for air support or in pairs on a Forgefiend for heavy support, the Hades Autocannon (R36", S8, AP4, Heavy 4, pinning) suffers the Reaper's slightly gimped range compared to the vanilla autocannon, but is slightly stronger and can pin units (but don't count on pinning too much); while it's not twin-linked like the reaper, having double the firepower more than compensates. A Forgefiend can mulch most infantry short of Terminators, pounding through power armour on sheer weight and power of fire, can make most Monstrous Creatures' lives flash before their eyes, and can hurt even a Land Raider or Monolith. It's almost really a shame that the average Forgefiend isn't known for being a phenomenal shot.
Assault Cannon
The Assault cannon is an Autogun with an outrageous rate of fire, meaning it has to have rotating barrels to stop them from melting. Although it falls far short of it's terrifying fluffy firepower on tabletop, firing 4 shots compared to the 10 and 20 shots of imperial Gatling cannons. It also fires unique, diamond-hard rounds at significantly increased velocity, resulting in far greater stopping power and penetration. The upgraded weapons system was found post-Heresy, meaning that Chaos doesn't get these meat-grinders (although Obliterators do). Primarily used by Space Marines as anti-infantry weaponry on Terminators, Dreadnoughts, and various other vehicles and aircraft. The assault cannon might actually be a stub-weapon, as some art shows it ejecting spent casings. Only War and several other sources show that there is a difference. Auto-weapons are (usually) caseless and can be anything from merely caseless, chemically-propelled rounds, to railrifles and gravitic-accelerated projectiles. This is also why Macrocannons are auto-weapons, as their shells are magnetically propelled. Of course, knowing the Mechanicus, there are probably examples of both auto-weapons and stub-weapons for all solid-projectile weapons of the Imperium.
Rotor Cannon
It should probably have been named Rotor Gun instead, to avoid insulting the true cannons. The ancestor (feeble grandparent) of the Assault Cannon, firing smaller-caliber, less-capable ammunition and to date only seen in 30k. Unfortunately it is much weaker than its more recognizable descendant, with only half the stopping power (in fact it is on par with the standard Autogun and outclassed by the Heavy Stubber) and much less armour-piercing ability, despite having the same shot output most of the time. About the only advantage it has over the Assault Cannon is the fact that it is man-portable by both Power-Armoured Astartes and unaugmented humans, whereas the Assault Cannon requires the user to wear Terminator armour or a vehicle mounting. Based on the stats, it presumably fires similar rounds to an autogun (which is analogous to a modern battle rifle) but at a much higher cyclic rate, so it probably has some similarity to an M134 minigun.
Punisher Gatling Cannon
The most dakka in the game that isn't the Titan mounted Vulcan Mega-Bolter. In fact, so much it doesn't go "dakka, dakka" it goes BRRRRRRRRRRRRRRRT. Able to churn out more shots than a squad of Tactical Marines at even greater strength, this baby will melt down any block of infantry it comes across and can even threaten Monstrous Creatures by the sheer volume of fire they put out. Also has a kid brother in the form of the Taurox Gatling Cannon, which has less strength and half the shots.
Gatling Blaster
Strapped to the mighty Reaver Battle Titan and above, this is the weapon you field when you need the biggest dakka the Imperium of Man has to offer, it's basically an Assault Cannon, except that it fires Battle Cannon shells rather than bullets, yeah... this is what you get if you thought about the Schwerer Gustav using Gatling Technology. Now if only they had some kind of Macro Gatling, ridiculous as that would be.
Macro Cannon
The Biggest of the Big. 'Macrocannon' seems to be a catch-all for any auto-type weapon larger than a Gatling-Blaster, ranging from fortress-mounted field artillery to the literally apocalyptic, cathedral-sized weapons found on voidcraft. As is clearly evident, it causes a quantity of Rape proportional to its size, but even the smallest land-based Macrocannons are capable of laying waste to mostly everything, including flyers. It is at its basest an autocannon that fires bullets ranging in size from that of a man all the way up to the size of a Baneblade, depending on the weapon's calibre (no, seriously), and since this is the Imperium, instead of an automatic reloader, they need dozens of slaves to move each bullet for the ship-mounted Macrocannons (heretical theories suggest this is either because it is actually cheaper for the Imperium, which is overloaded with humans and not resources, or because they are stockpiling resources, or they are cutting down on chances of daemonic incursions through humans by putting more of them in the killzone, or they are testing to see just how far people will comply with slave labor in a totalitarian state, or - most heretical of all - some suggest it is a bureaucratic screw-up with paperwork or that the AdMech doesn't know how to repair the loading cranes). Provided yields for these weapons can go from 42 exajoules (about 5.297 times more powerful than most powerful earthquake ever recorded; a 42 exajoule earthquake would be approximately magnitude 9.98) right down to the measly 50 tetrajoules...*sigh* Games Workshop never fails to surprise us. Seriously believe us, we know that tetrajoules isn't an official unit of measurement, but since tetra is Latin for four this essentially gives us....4 joules of power....which is weaker then a human punch or a flashlight.... Don't believe us? We got that from Rogue Trader rpg: BattleFleet Koronus pg. 31 & 20 which is quote on quote:
- "Look at her, son. Isn’t she a beauty? Over two hundred Vulcan mega-bolter defence turrets, fifteen tetrajoule Sunsear las-broadsides, prow plating ten metres thick, the finest auspex masts in the battlefleet… And the lines on her! Fluted prow, elegant statuary… those xenos scum won’t know what hit them!” – Bosun Phineas Jhule tempts fate at the embarkation of the Fire of Heaven
- "The Avenger dates from an earlier period of fleet tactics, when, squadrons of grand cruisers were employed as “line-breakers.” Traditionally, they were thrown into the midst of massive fleet engagements, soaking up enemy fire while racing into the middle of enemy formations, then crushing their opponents at short range with tetrajoules of energy from their oversized broadsides."
Yeah...we in /tg/ aren't sure whether this was intentional or a gross example of a severe typo. So...um....FEAR THE 60 JOULE BROADSIDE BATTERIES! Jokes aside, if we use the picture to the right as a reference for size, and estimate the shell as a solid slug of density equivalent to lead, launched at a planet from geosynchronous orbit above an Earth-like planet (36,000km), you're looking at somewhere in the region of 50 Tera-Joules of energy when it strikes the ground, or slightly less than the Little Boy dropped on Hiroshima (and that's just from gravity, not including launch energy). About fifty or so of the land-based Macrocannons would equate to one ship-mounted Macrocannon, or one point of firepower in Battlefleet Gothic. Oh yes.
Gallery
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Autoguns - Better Than Your Crap Flashlights!
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A typical mass produced model.
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Traitor Guardsmen armed with Armageddon-pattern Autoguns and Autopistols. You know you want 'em.
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The Punisher Gatling Cannon and its tank. Sometimes you just need a little more gun.
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The Gatling Blaster. For when you need big dakka.
