Cymbel said:

Take a look at either Black Crusade or Only War and you'll get this line:

An autocannon is a crew-served heavy weapon, a self-loading high calibre cannon that uses dense solid shells to punch through armour.

Note that these are both far more recent sources than the one you cited. Also note that ALL autocannons (including the one from the Inquisitor's Handbook) do Impact damage. If they were meant to be firing explosive shells, then the damage would be of the Explosive type.

Boss Gitsmasha said:

It's never wise to assume that Imperial technology can bridge even the tinniest gaps. To them the ammo for an assault cannon and the ammo for an autocannon are quite different. The range of the Autocannon is also far greater than that of the assault cannon, so it likely fires its rounds at higher velocities - which is something that would benefit firing solid slugs far more than explosive rounds.

Incidentally, the assault cannon also inflicts Impact damage. There needs to be a change to either the damage type (to Explosive) or to the fluff that says it uses explosive rounds.

HappyDaze said:

So? The autocannon can fire solid shells and for armor piercing duties, those are great, but it doesn't say anywhere there about how they are unable to fire explosive shells, nor how the tech to them is lost beyond the grasp of man. On the damage type, it could be a typo, FFG may make great books, but there are definitely mistakes within them.

However, why don't we get an answer from FFG? Or at the very least show sources from other FFG works showing that explosive rounds in Autocannons never ever exist or are ever used, ever. Besides, this is 40k, the canon and tech are so schizo at times that some worlds use solid shell autocannons, others explosive, most a mix

Edit:

http://wh40k.lexicanum.com/wiki/Autocannon#.UOYxYqNOztQ

The best source for 40k canon says they fire both

Cymbel said:

Why don't you show me a single example of an Autocannon statted up to do Explosive (X) damage in an FFG book? I don't think it's a typo when all of them consistently do Impact (I) damage.

As for Lexicanum, I don't consider it the best source for anything related to the RPGs.

And the other ones use solid shells only, of course they do impact. I was just saying it COULD be a thing on this one, knowing that they use explosive ammo in them.

Lexicanum is a great source for 40k fluff and acknowledged as one of the best to be honest. And look, I showed you a link with sources that said Autocannons fire explosive ammo. Can you find me sources where there never can be an autocannon that fires explosive ammo ever? And that Autocannons can ONLY fire solid slugs, because the Imperium has no ability to put an explosive inside a large shell?

Cymbel said:

I would dispute that point. While 40K obviously has some pretty strict limits on how they use computers and computer equivalents, the things they can do with them are pretty **** awesome. Sure, they don't hook everything up in networks (because that would be just asking for scrapcode and such to do horrible, horrible things to them), but something like the MIU or cyber familiars or the various other augmentations and implants (or, hell, the semi-ai in some Imperial vehicles) are certainly not inferior to modern technology. I'd say that, as with most 40K things, they have stuff that is inferior to modern stuff, stuff that is at modern levels, and stuff that is so far beyond modern stuff it's flat out amazing, at varying levels of use in various places, with higher-end stuff mostly confined to the the Mechanicus. Although it's not necessarily developed along the same line as our technology seems to be developing, given their love of organic integration, servitors and the like..

Of course that's disregarding the question of whether Machine Spirits are real and if so, just what they are, which may place their technology either higher or lower on a theoretical technology scale.

They do Impact damage because they're SP weapons. This means that the solid slugs are likely the "default" ammunition type. Obviously, if you want them to fire explosive shells, change the Damage type to (X). I don't see what's so difficult about this. Bows are capable of doing (X) damage even though they're statted up to do ® damage, by virtue of explosive arrows.

Besides, weapons are perfectly capable of accepting different kinds of ammunition, and these different kinds of ammunition may alter a weapon's default stat line in a way. You're arguing over nothing.

Apocalypse, Pg.107

The Hydra Flak-Tank is a specialised vehicle used for mobile air defence, based on the Chimera chassis. The Flak-tank can often be seen defending Imperial Guard columns and artillery positions from arial attacks, its long-barrelled autocannons sweeping the skies and unleashing a hail of explosive shells

Imperial Armour Volume One - Imperial Guard and Imperial Navy, Pg. 171

…, its four long barreled auto-cannons sweeping the skies and unleashing a wall of explosive shells .

Imperial Armour Volume One - Imperial Guard and Imperial Navy, Pg. 205

(Shows various Autocannon shells, no further details given)

Multiple descriptions of Autocannons firing explosive rounds AND having multiple rounds for different effects. And guess what? There is no issue with them using solid rounds, solid rounds have superior effects in some situations, like penetrating armor, while explosive rounds would work better in other situations.

On the heavy stubber being a small caliber, doesn't it look like this? ( http://en.wikipedia.org/wiki/M2_Browning )

Which, like the Heavy Stubber is used, is a heavy machine gun and a pintle weapon (though as an infantry weapon Stubbers are used less, mainly due to the heavy bolter)

Cymbel said:

Nope, to me, it's more like this:

Or, for man-portable (with the option for a tripod) like this:

Those are both .30 cal M1919s (an A4 for the first, and an A6 for the second).

Really?

They seem pretty big to me

The second image you show is most certainly more appropriate for an autocannon, but here's a picture from Lexicanum (I loathe to use them, but it'll do):

As for an autocannon, look at this:

That sure looks similar (aside from a different ammo cassette) to the twin-linked weapon the Death Korps were using in your image.

First off, pictures without scale don't help us, so let's stick to official ones where they are holding them

Heavy Stubber (4)

VS

For a direct comparison in size with the same model, the same trooper, same perspective. What we can see is:

HEAVY STUBBERS ARE HUGE

Which fits the fluff, they are massive machine guns who use the antiquated stubber ammo (so have to be bigger to compensate).But they are used because they are cheap and hit pretty hard still, though not the most effective weapon.

Back to how big autocannons are

Just for comparison's sake, here is a Heavy Bolter

Cpt. Harkonnen said:

50 calibre weapons are common in 40k.