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Some guy did a really great post awhile back on the mathematical odds of killing something using a krak missle vs. an auto cannon for different toughnesses and armor saves. I've tried searching the formum but haven't found it, little help?
I don't know what the post was like, I assume it had heaps of different calculations for different targets, but it's not hard to work out.
For any one-shot weapon, the chance of it killing something is:
Chance to hit x chance to wound x chance the target fails its save.
For instance, a Krak missile against a Terminator, fired by a guardsman is:
1/2 hit x 5/6 wound x 1/6 failed save = 5/72 = 0.069 = 6.9% = bad odds
Or for a Marine:
1/2 hit x 5/6 wound x 1 failed save = 5/12 = 0.416 = 41.6% = decent chance.
The "1 failed save" is because he has a 100% chance of failing his save, since it gets ignored by the Krak missile. If armour saves are ignored, you can just leave that bit out all together.
Now, for multishot weapons, there's 2 ways of doing it.
First, if you just do the above and multiply by number of shots, that will give you an expected number of kills, which you will average if you did the same thing hundreds of times. So if I fired 100 krak missiles I'd expect to kill about 42 Marines.
If you're trying to work out the probability that a weapon will kill a single model, then you need to work out the probability that it WON'T kill the model, then subtract that from 1.
The reason for this is that you don't need both shots to hurt the model in order to kill it. One or the other or both will do. There's 4 possibilities:
1: Shot A and Shot B both fail to hurt him
2: Shot A hurts him but Shot B doesn't
3: Shot A doesn't hurt but Shot B does
4: Both shots hurt
If it's a single wound model, then any of 2, 3 or 4 will do. And if you add all those probabilities together, you get 1. That's why it's easier to just work out the probability of failing to hurt him (option 1) and subtract it from 1, since working out the probability of any given shot failing is annoy and hard, because it can fail on the roll to hit, to wound, or to save.
Autocannon at a Marine:
Probability of a single shot killing:
1/2 x 5/6 x 1/3 = 5/36
Therefore, probability of NOT killing:
1-5/36 = 31/36
So the probability of 1 shot not killing is 31/36. Therefore, probability of 2 shots not killing is:
(31/36) x (31/36) = 74.2%
So the probability of killing the marine with 2 shots is:
100% - 74.2% = 25.8%
Apologies if my explanation is a bit convoluted, but that's how to work out all the probabilities. With some practice you can actually work out the 1 shot probabilities pretty quickly. The important thing that a lot of people don't consider, however, is that multishot weapons have more POTENTIAL.
A missile launcher will get 1 kill or 0 kills. But a Heavy Bolter has the POTENTIAL, although it may be unlikely, to get up to 3 kills, even against Marines. This is why I believe that if you're ever torn between the high strength, 1 shot weapon or the medium strength multishot weapon, go the multishot. (This doesn't apply, of course, if you're taking the high strength weapon for a specific purpose that the medium strength one can't fullfil, such as Landraider killing)
I belive this is the article you're looking for:
but I'd take the HB in this case instead, as it costs less, and you have one more shot.
36" is enough most of the time and S5 wounds a marine on a nice 3+. Plus, one point of strengh is wasted on marines with the AC (S7) as it only takes S6 for a 2+ wound.
that is, if your not planning to use the AC on vehicles. nevertheless, why not simply include both, HB and ML, you'll always have enough anti-tank and anti-infantery weaponary.:w00t:
Thanks Kaiser, that's what I was looking for.
The autocannon is a light vehicle killer and nothing more then that,sure it can kill troops if you need it to but thats what the heavy bolter is for as it fills this role a lot better.
The Missile Launcher can do two things just like the autocannon as it can tank hunt and aslo is a great marine killer as it has near a 50/50 chance of killing one. Aslo its a lot cheaper then a lascannon and is not such a large target for the enemy but i would still have 2 or 3 lascannons to act as big game hunters.
"Hey sarge, this lasgun is heavy. I wish we had something lighter."
FF7: ABOUT RANDOM BATTLES