Why do CSM use Autocannons, but Loyalist Marines dont?

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**Lathe Biosas**

Is there a in universe reason or was it simply a way to differentiate CSM and SM units on the tabletop?

**Mad Doc Grotsnik**

Chaos Marines rely on more robust equipment because they lack the same resources as a Loyalist Chapter.

The Autocannon is a pretty fine weapon, able to carve up infantry and a threat to anything except the heaviest of tanks. They’re also robustly built, and easy to maintain including ammo. So when you’ve limited logistics, they’re a solid choice.

A Chapter has the ways and means to maintain more finnickity weapons. So it just doesn’t face quite the same compromise as renegades.

**Ashiraya**

I don't know what the original reason was, this is old old stuff. It probably was to make them more distinct.

In-universe, it's probably cultural and practical. Autocannons were popular with Marines pre-heresy, but the Blood Angels and Imperial Fists experimented with infantry-sized assault cannons that after the Heresy became reliable and popular.

By that point the traitors had already sodded off, so they kept their autocannons instead.

In lore there are probably loyalists with handheld autocannons and traitors with assault cannons, here and there. But it's rare and non-standard, so doesn't get a model, and because it doesn't get a model, it's not exactly a priority for depictions in novels and art.

**Mad Doc Grotsnik**

Assault Cannons require maintenance and new barrels after every engagement, and are ammo hungry by their very design. So again for largely piratical forces? They’re not the most cost effective weapon you could equip.

**Ashiraya**

Though that only really applies for Terminators. Vehicles and Dreadnoughts are noted to be able to carry so much ammo that the sustainability problem is no big deal.

The barrel still wears out after about ~50k rounds, but that is a -lot- of dakka.

**Mad Doc Grotsnik**

It’s still a specialist weapon.

When Marines go Rogue, it’s only rarely a significant portion of a given Chapter. So those lads are more or less immediately severing ties and departing without the Serfs and Forges etc. And when a whole Chapter turns? If they’ve a homeworld, it’s likely to be attacked by a vengeful Imperium, at the very least impacting its repair and rearm capacities.

You’re then having to deal with other renegades, including the Dark Mechanicum for resupply - or rely on piracy.

It really is simple logistics. Assault Cannons and Anti-Grav are time and resource intensive to maintain and repair. When your resources are now inherently limited? It makes sense to trade down to still robust and deadly weapons which don’t require so much mucking about.

**Ashiraya**

You're overthinking it, I think. The Reaper Chaincannon exists and is a very common CSM weapon, to say nothing of the rotary Hades cannons used by Heldrakes and Forgefiends.

Chaos can maintain and supply rotary cannons. As I said before, it's mostly cultural. They mainly use their own guns, CSM using assault cannons is rare enough to not get models and therefore doesn't feature much in art and lore.

**Iracundus**

From the 2nd edition Chaos Codex:

When the Tatiro Legions rebelled against the Emperor the far-flung Imperium was already in a state of flux as it tried to assimilate the lost knowledge and vast resources recaptured in the Great Crusade. THe forces of the Adeptus Astartes were in the process of re-equipping their forces with the masses of newly forged armour and weaponry pouring out of the workshops of the Adeptus Mechanicus when Horus unleashed his Legions.

As a result, the forces battling in the Horus Heresy fought with a mixture of the sometimes archaic armaments which they had used during the Crusade and previously unknown weapons based on arcane ancient technologies. Because the Traitor Legions were the ones that had advanced furthest from Terra they wre among the last to receive new weapons and armour. This meant that the Space Marines fighting for Horus lacked many of the weapons which would be subsequently phased into the arsenals of the Imperium over the next millennia.

After Horus fell the Traitor Legions were driven into the Eye of Terror, untouched by the flow of time. Their weaponry and armour has been embellished and decorated with personalised schemes but otherwise it has stayed unchanged down the centuries as they fight the Long War. Innovation and invention have become anathema to Chaos Space Marines as they battle the hated Imperium. They preserve their bitter anger for the lost millennia forced on them by the Emperor and anything new serves only to drive the shards of their hatred deeper into their tortured minds.

...

When the Legions began re-equipping, a number of weapons which would come to be in common use later were still experimental or even purely theoretical. Many other weapons relied on sciences that were barely understood but which had been found in ancient vaults of dark technology and copied for general use. For example, the Traitor Legions had no access to Melta bombs or multi-meltas, but melta-guns were commonly available. Likewise, portable (though dangerous) plasma guns and even pistols existed but the heavy plasma gun could only be mounted on a Draednought or a vehicle.
...

Autocannon were favoured as simple but deadly weapons that could easily be easily carried by a Space Marine in power armour.

p. 71, 2nd edition Chaos Codex

The Traitor Terminators, lacking the technology and equipment to maintain the notoriously fickle Assault cannon, still make use of the Reaper with its simpler mechanism and solid ammunition.

p. 73, 2nd edition Chaos Codex

Designer's Notes

Another interesting spin we came up with was to make the Chaos Space Marine forces feel as if they had been exiled to the Eye of Terror ten millennia before the Imperium's 'present' day. Though the technological advancement of the Imperium moves at the speed of an aged tortoise ten thousand years was bound to bring some changes. This suggested limiting the Traitor Legions' weaponry to some of the 'older' types and making others dangerous, experimental precurors of the guns used by Imperial Space Marines. This, combined wit hthe older patterns of power armour the designers have used, gives the Chaos Space Marine miniatures a dark, archaic feel which contrasts wel wit hthe clean, upright loyalist Space Marines.

...

Andy Chambers

p. 112, 2nd edition Chaos Codex