Siranui said:

23mm actually, and untill someone says specifically otherwise autocannons are 30mm+explosive, and seeing as 30mm is easily enough for grenade like aoe that some kind of directed charge.

If we want to be picky, then aren't. HBs 1" cal, and 1" = 25.4mm?

Autocannons by today's parlance are anything over HMGs (12.7mm), which tends to mean that they start at 20mm, not 30mm.

Siranui said:

That's fair enough, but the average autocannon as shown is clearly more like 30mm based on all the recorded damage stats from DH and TT and just comparative looks. It's safe to assume that there are smaller calibre ones available but there's no reason to assume the average is man portable because heavy weapons have long since stopped being man portable. Smaller weapons could be used to make them easier for a team of men to transport. The idea of them reducing a autocannon caliber from 30mm to 20mm to make it man portable is, IMHO, laughable and certainly no reason for a Space Marine to worry about man portability.

I've got no problem with man-portable autocannons in the Deathwatch. They are by their nature a very unconventional unit that uses unconventional methods to achieve victory. I'd likely just have them available to Marines in Terminator Armor, like the Assault Cannon.

I'm not convinced that a conventional 30mm munition would be in any way superior to a 25mm conventional munition with a rocket booster (which is what a heavy bolter is). So I don't really see why any cannon in the 30mm range would be any better than a HB. In fact, it'd probably be worse: The HB can carry a larger warhead and/or a greater velocity without the normal recoil issues of a similar-powered conventional cannon, due to the rocket propulsion.

Which means that in order to get the increase in POWAR that everyone wants (ironically while others complain that the HB is too powerful...), we're talking 40mm shells at least. Full auto! That's frankly pushing it a bit further than I'm happy to go, given that Bofors 40mm cannons fire 2lb shells and weigh a metric ton or more!

PrimarchX said:

It's exactly what Termi suits were equipped with around the Horus Heresy, and what Chaos terminators use in the current period. The Imperium ditched them for the superior Assault Cannon.

Siranui said:

Bear in mind that a rocket the same size as the shell that leaves the muzzle has significantly smaller warhead because you also have the propelant in their as well. Plus of course a small increase in diameter is a large increase in volume if it scales up in all directions. So an item that is twice as wide, twice as high and twice long has eight times the volume.

As an example the 14mm russian heavy machine round is 1.3mm larger than a 12.7mm, .50 cal round and yet has twice the kinetic energy.

Bolters don't give you a bigger warhead for the same size bullet as conventional firearms, what they give you is the ability to fire much larger bullets than you could normally because they can be fired out the barrel very slowly and speed up afterwards.

The autocannon in the TT is primarily used to take out light and medium vehicles, a 30mm cannon IRL will take out anything short of an MBT (and hitting weak armour with enough of the right ammo even tanks) and I don't think that's co-incidence.

Siranui said:

You can't compare Bolt which are rocket propelled grenades with a 30mm SABOT shot.

Bolt are explosive and have mass reacting shells etc. Very dangerous against infantry armors etc.

Autocanon are typically sabot shots, they bunch a big hole or nothing since the head is a simple hard sabot shell made for impact, hence the ST 7 P 4.

The reaper autocanon was a pre-codex configuration, since codex is written post hesresy, it's argualble that a few chapter still carry over those weapon from pre-codex hera as relic.

Autocanon won't jam as often as an assault canon like storm bolters to is oldder brother the combi bolters..

Autocanon are totally man portable and a weapon of choice of the Imperial guard, they are mounted on the many vehicles they have and also by weapon teams.

Autocanon are a cheap version of the assault canon, assualt canon are not typical devastator weapon for the amount of ammo they must use, where autocanon use less but bigger ammo, they are usually mounted on dreadnought or tactical dreadnougth armors (termites).

Reapers autocanon are dreadnought and Termite only (chaos too) and the man portable is a single barel weapon.

Face Eater said:

It's noted in Imperial Armour 2 that bolt weapons employ a conventional propellant charge to eject the shell from the weapon before the rocket fires. The justification there is that it prevents the barrel being subjected to overpressure from the rocket, but it would also significantly increase the weapon's muzzle velocity and prevent someone from stopping a Heavy Bolter firing by putting his hand over the end (which, given how frequently Bolters and Bolt Pistols are depicted as being used at extreme close range, makes sense... otherwise a Commissar putting a bolt pistol to a man's head to execute him would result in pathetic and embarrassing failure).

Face Eater said:

Bolters are the next technical generation in the universe. They would not exist if they were not better than a comparable conventional weapon. No science is needed for that much to be obvious. You don't invent an automatic weapon with horrifically complex ammunition and equip the finest troops you have with it if something the same size, using far simpler technology does the same job better.

There is no reason for a bolter warhead to be smaller because - as you say - the reduction in recoil impulse can result in a LARGER warhead being used. You launch using a low-power conventional charge to reduce recoil, then accelerate. There's obviously no point having such a complex design unless the warhead size is substantially better than it would be conventionally, otherwise there's no point in the design. And of course: Un-used rocket propellant becomes extra warhead, too.

Yes: 30mm does a great job at chopping up light armour, but so do HBs. You haven't illustrated why autocannons would be at all better than 25mm bolters. And you can most certainly compare a 25mm HEAP warhead with 30mm sabot. If anything HEAP is better over range because it's penetration isn't dependant on velocity. Sabot rounds shed their relative lethality much more quickly.

What kind of autocannon are equipped to Imperial guard? Taking a step away from the TT into commonsense-ville, I mean. 20mm at most? Or are we suggesting that mere guardsmen fire fully automatic cannon that are larger in calibre and more lethal than the heavy bolters fired by bio-engineered, power armoured astartes? Because that just doesn't work.

Sorry, but once again, I feel that trying to stat an autocannon to be better than a HB makes no sense to me, unless it's a truly fearsome weapon... at which point it starts to become a Reaper... and those are supposedly inferior and outmoded by assault cannons, so shouldn't really be better statted than those... and will need a Termi to mount onto. We might as well be discussing stats for a Marine autogun and making it better than the boltgun.

Siranui said:

Consider it this way: the Imperial Guard use heavy bolters too... and the Autocannon is (and has always been) a slower-firing, more powerful alternative. If you look at the current models, the autocannon in the Cadian and Catachan Heavy Weapon sets (and those in the Krieg range from Forge World)... is longer than the operators are tall, by a significant margin. It's not a small gun by any stretch of the imagination, and except for those carried by Chaos Space Marine Havoks, and a single Necromunda model, they're always shown as crew-served guns.

Considering that Autocannons are also employed extensively on vehicles (ranging from the single Autocannon employed on rare Chimera variants and the Astartes' own Predator Destructor, to the Exterminator and Hydra variants, and their use on most common forms of Imperial Navy atmospheric craft), many of whom also employ Heavy Bolters, clearly there's a reason to keep using the Autocannon in some contexts. It may have fallen out of favour amongst Astartes Devastators (it was an option back in 2nd Edition, but is no longer), but the Imperium as a whole uses a lot of Autocannons. There must be a reason they keep using it when heavy bolters are no less commonplace on vehicles.

The HB is designed to be used on full auto. That eats ammo like crazy over longer fights and it's complex, hard to build ammo.

The Autocannon can sometimes be useful on singleshot, too. And if firing full auto it's stimm only half the rate of fire and the ammo is much simpler to build. These two points are enough reason to keep using it in warfare.

On the power level:
Per shot the HB and AC to similar damage. The just use a different method to do it. While the AC can do lots of damage it can do little as well because it has more dice but a lower bonus and lower pen. So in a certain way the HB is more reliable to do what is expected of it while the AC is more like a gamble.
And on top the HB shoots a lot more bullets, so while they may be similar per shot all in all the HB is better if you are not in the danger of running out of ammo.

Why do I think the HB and AC do similar damage?
The mean result of a d10 dice roll is 5.5 for non tearing weapons. That is the mean of min and max roll. For tearing weapons it's more complex but for a weapon with 2d10 that is tearing I would approximate it by taking min, max and mean roll and taking the mean of the higher two. so 1, 5.5 , 10 or 15.5/2=7.75.
If I just add the pen to damage for comparison you get the following:

AC has 4x5.5+5+4= 31 mean per shot damage including pen
HB has 2x7.75+10+6= 31.5 mean per shot damage including pen

HB has damage X, Autocannon hast I, so vs hordes the HB does more horde damage per hit.

And it's got the double max rate of fire, the bigger clip size and the shorter reload when using clips.
All in all the HB is the superior weapon. But still there are situations where the AC excels. One of those things is saving ammo, the other is range.

Umbranus said:

A nicely considered arguement, and pretty close to the truth given your approximations. incidentally a back of the envelope style computer program has told me that the mean value for 2D10 tearing is 13.475 (not including rf but rf wasn't included for the autocannon either) so the HB damage is 29.475 which is approximately equal to 31. I still think that righteous fury would make the autocannon more lethal

And yeah its definitely true that an autocannon is only really astartes portable, it would have to be lugged around and fired by like 2-3 guys otherwise. part of the problem is in ffg's representation of rapid fire. the auto cannon is probably about right but heavy bolters can really fire much faster than 2 times a second and so can assault cannons. I'm pretty sure i've heard bolters can empty their clip in 5 seconds.

anyway im gonna do some rf sims and come back with damage

quick question, if all 3 dice come up a 10 do you apply righteous fury and then remove the lowest die? or do you remove the lowest die (which is a 10) and then apply righteous fury. and similarly if you get 10, 10, 9 and then RF gives you a 3 and a 4 can you remove the 3 as the tearing die?

Sorry I made a mistake in my above post, RF only ever gives 1 extra die that can explode. but I think my question still remains,

if I rolled 10 9 8 and my rf die was a 5 would I remove the 5 because its the lowest die overall or the 8 because its the lowest die in the initial damage roll?

Narkasis Broon said:

I would say no, 'cause it's a different die-roll.

Siranui said:

Yeah, I know that. You purport the Assault Cannon is 'superior' and maybe for some purposes it is. But for some situations it may well be the right weapon at the right time. Hence if one of my players wants one and has the Req/Rep then it would be available to them.

PrimarchX said:

Well the assualt cannon is pretty **** awesome, in a way I think it's doesn't get across the power that it has in the TT, but also I think a more direct comparison is the Cyclone missle launcher. Firing Krak's, in the TT at least, it's like an auto cannon but superior in strength and pen (although of course a Reaper AC is twin linked).

Still say, cut down the RoF of the Autocannon to -/-/6 and give it the Storm ability, such a weapon should be fired in short controlled bursts.

The reason why the "normal" Space Marines only use mounted Autocannons is because it is also one of the mainstay weapons of the CSM, its all about symbolism.

S.

Siranui said:

Personally I would give autocannons a RoF of S/2/4. I don't see it as a fast firing automatic weapon. More like a RARDEN gun (the old 2nd edition carriage ones were even magazine loaded). Maybe even S/3/-.

I hate this quoting system...

I like the Autocannon just like it is.
And my Hammers of Dorn Devastator will have one as signature wargear.
It will work nice with immovable warrior, eye of vengance and red-dot laser sight.

Not the usual horde-killer dev but I think it will be fun.

Umbranus said:

Except that firstly the A/C will statistically cause MORE damage, because the greater number of dice shift the likelihood of RF upwards.

As for the range... a 300m weapon pretty much out-ranges everything else in the game by a massive margin. Odd, considering that we were discussing saboted rounds (which are relatively short range) compared to self-propelled HEAP rounds (which are going to have a far greater lethal range.

And the reduced rate of fire is often moot, considering that in order to receive the bonus for having it, you need to hit by more than 60%.

Basically, the way you've statted the A/C just makes it pretty much better than the HB. The HB should be the better weapon in 90% of situations, hands down.

As for giving it Storm... that just makes it even better.

If you really want an A/C, then it should be better against medium-armoured vehicles, and a worse option than the HB for everything else. It's what A/Cs are for, and it's why they are mainly mounted on vehicles.

btw taking into account RF a heavy bolter 2D10+10 pen 6 tearing inflicts an average of 31.131155 damage including pen

An auto cannon with 4D10+5 pen 4 inflicts an average of 33.101091 damage including pen,

This was calculated using a simple for loop summing over all possible values of the initial dice roll along with the assumption that if you roll at least one 10 you do an extra 6.1111111 damage (this is the average damage that an exploding d10 will roll)

the damage difference is less than two points per hit. this means that in most cases if the heavy bolter gets even one more hit than the ac it makes up for the damage. It is relatively easy to stack sufficient bonuses that you have a net gain in damage from wielding a heavy bolter instead of an autocannon. for example just bs 50 firing on full auto means that you need 20% or less to inflict more damage with the heavy bolter, and you inflict so much more damage with the heavy bolter that it averages out all of the damage that you lose in the 21-70% region

If we want it to be good against medium tanks would it be better to say remove one damage die but make the auto cannon pen 9?

I agree with siranui that giving it storm is too much, even the reaper on the defiler only has twin linked.

And finally I would be the first to say I know nothing about real guns, I'm not a marine or even an amateur enthusiast, I'm British and the closest thing to a gun I've even held is an air rifle, however at long ranges is it really about stopping power? I guess it is in real life, but in this game the weapons don't get weaker over distance, just less accurate. might a bolter shell drift more over long ranges than an autocannon shell? or is the decreased accuracy to represent the chance that it might hit the target but just do nothing?

All firearms in 40k are horribly inaccurate. It seems the 300m range was just plucked out of thin air, to be honest.

For all the talk, I'm not seeing a weapon designed as a medium armour-killer. I'm just seeing something being invented that's better than the HB. It's not an 'alternative choice for specific missions' but an upgrade.

Every time someone does the math the result is that the Autocannon is only marginaly better on the ber shot basis than the HB.
It is a fact that the HB can fire more shots
There is more special ammo for the HB than for the AC.
There are talents who boost bolt weapons (Bolter drill, storm of iron) and SM special abilities (Bolter Mastery) and Attack patterns (Bolter assault) and yet some people stimm say that the AC is better than the HB.
The HB is a horde killer, the AC isn't because it lacks the explosive damage type and fires less shots.

Do you have arguments that support this claim or is it just that you don't want to admit that you're wrong?