Probability of Destruction

[I picked this up off www.yesthetruthhurts.com]

I'm trying to answer the question: "What is the probability that a given weapon will destroy or immobilize a vehicle on one round of shooting?" As a newbie Sisters player, I've tried to run the numbers for an Exorcist, and I'm gonna run the numbers for other popular weapons as soon as I verify my numbers. I know that my formula doesn't account for multiple hits, but that only makes these estimates conservative.

In your experience, do these numbers sound about right?

Probability that an Exorcist destroys the given vehicle armor value in one salvo:
AV 10
Destroy: 57.51%
Immobilize: 69.59%

AV 11
Destroy: 48.13%
Immobilize: 60.25%

AV 12
Destroy: 36.75%
Immobilize: 48.13%

AV 13
Destroy: 22.95%
Immobilize: 32.44%

AV 14
Destroy: 6.26%
Immobilize: 12.2%

Any help appreciated,
Fifthman

P.S.: If you're a statistics kind of guy, here's the way I calculated the values:

Probability of a single missile dealing the desired damage (P1):
Easiest calculation, should be straightforward.
P1 = (P to hit)*( (P to penetrate) * (P of desired damage) + (P to glance) * (P of desired damage))

Probability of n missiles dealing the desired damage(Pn):
This is where the multiple hits issue comes in. The formula assumes, basically, that only one missile actually hits and the other n missiles miss.
Pn = sum from 1 to n of (1-P1)^(n-1)*(P1)

Probability of a salvo dealing the desired damage(Ps)
The probability that a number of missiles is fired is 1/6, and the probability that the given number of missiles is fired is Pn.
So, Ps = 1/6*P1 + 1/6*P2 + ... + 1/6+P6, or simplified to
Ps = 1/6* (sum from 1 to 6 of Pn)