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I'm trying to figure out the calculations for probabilities to wound on a Predator (toughness 7, save 3+), but am not sure if I'm getting it right..

looking at the following heavy weapons stats for str / ap / damage, how would I calculate the most probable outcome for amounts of wounds in 1 turn on an opposing predator tank for each weapon?
plasma cannon: heavy d3 / 8 / -3 / 2 / (dies on roll of 1)
missile launcher: heavy 1 / 8 / -2 / d6
lascannon: heavy 1 / 9 / -3 / d6
multi-melta: heavy 1 / 8 / -4 / d6 (within 12’’ roll 2d6, discard lowest)
grav cannon: heavy 4 / 5 / -3 / 1 (d3 if save of 3+)

If we take the lascannon, I'm thinking it would be 1 shot x .66 (bs is 3+ to hit), so it = .66 chance to hit. Then x by chance to wound (+3 in this instance), so .66 x .66 = .435 % chance to wound.
then x by chance of armour save, which is 6+, so a .833% chance of being a successful shot. so .435 x .833 = .362
so 36.2% overall probability of wounding? And then a median of 3.5 wounds for each successful shot. Is that correct?

And if so, how would I apply this math to the plasma cannon with heavy d3? the same way?

 benlac wrote:
I'm trying to figure out the calculations for probabilities to wound on a Predator (toughness 7, save 3+), but am not sure if I'm getting it right..

looking at the following heavy weapons stats for str / ap / damage, how would I calculate the most probable outcome for amounts of wounds in 1 turn on an opposing predator tank for each weapon?
plasma cannon: heavy d3 / 8 / -3 / 2 / (dies on roll of 1)
missile launcher: heavy 1 / 8 / -2 / d6
lascannon: heavy 1 / 9 / -3 / d6
multi-melta: heavy 1 / 8 / -4 / d6 (within 12’’ roll 2d6, discard lowest)
grav cannon: heavy 4 / 5 / -3 / 1 (d3 if save of 3+)

If we take the lascannon, I'm thinking it would be 1 shot x .66 (bs is 3+ to hit), so it = .66 chance to hit. Then x by chance to wound (+3 in this instance), so .66 x .66 = .435 % chance to wound.
then x by chance of armour save, which is 6+, so a .833% chance of being a successful shot. so .435 x .833 = .362
so 36.2% overall probability of wounding? And then a median of 3.5 wounds for each successful shot. Is that correct?

And if so, how would I apply this math to the plasma cannon with heavy d3? the same way?

Thats generally correct, but understand thats the short hand way of doing it.

For the plasma cannon do the same but x2 either at the start or end makes no difference.

Count D3 as 2 and D6 as 3.5 and just plug them into what you already have.

Alright, according to my calculations the probabilities of wounding a predator tank in 1 turn with space marine heavy weapons are as follows:

points
21 - plasma cannon: 73% of 2wounds
25 - missile launcher: 29% of 3.5w avg
25 - lascannon: 36% chance of 3.5w avg
27 - multi-melta: 44% chance of 3.5w avg at 24’’, 44% chance of 4.5* avg at 12''
28 - grav cannon: 73% chance of 2w avg

*I'm not sure of Multi-Melta at close range, I just guessed the average would increase to around 4.5w's

My take-way's are:
-the armour modifier changes the probability to a much greater extent when using high-strength weapons. The difference between str 8 and 9 can be, and often is, negligible. But, the difference between a -2 and -3 ap modifier leads to a huge shift in overall chance to wound
-what isn't factored in here is the greatest potential for damage, which goes to the grav cannon; at a potential 18 wounds to dish out on 3+ a-save units
-the plasma cannon is surprisingly good, though with supercharged rounds you are risking a 16% chance of killing yourself every turn, unless you utilize hq's, characters or cp's to re-roll 1's
-the missile launcher seems like the worst option for consistently putting wounds on tanks
-grav is probably better than the mm, but it's hard to say. seems like most space marines vehicles have 3+ armour save, so it'd be better against those armies at least
-at range I would ideally take 2-3 las, and 1-2 plas.