In regards to odds to hit a tank...
33.3% Hit.
Then with a small blast, you have a "small" radius, plus the "radius" of your target, so let's say 3.0" altogether, on the narrow side of a Chimera / Rhino. Technically, you might do a little better, as certain placements can allow a larger scatter to still hit, as small portion of the time. So you then have a 66.7% x distance less BS on 2d6.
Assuming you have a BS 3 Model, a distance of "6" or less should generate a hit. [Large blast would be a 7
]
Soooo....
0.333 + [0.667 x 15/36] = 61.1% chance to hit, with a small blast.
Thanks!

Str 9 vs 12 has a 2/3 chance to strip a hull point so that's 40.73 hull points stripped. Huh. Interesting. That's terrible compared to the devourers, but there's no chance for a pen and no chance to damage AV 13+
Hm. I can see why people run the duel devourers.
Man, now I want to run 2 sets of 2 carnifexes. One brood full assault, and the other full devourers.
Bioplasma still isn't bad though, even just playing head games. But if I run that, I'm trying to think if there's anything useful I can do with the extra pair of arms. Deathspitter is cheap and has a good range.... huh. Hmm.... yeah, duel devourers. I see why people run them.
But against AV 13+... the only thing you can do it hope to assault them. Hmm. I'm arguing with myself at this point.
..... Now I want a tyranofex with a rupture cannon. I'm so sad that I'm poor....
---------Edit------------
Here's a list that I'm pretty happy with with my current collection. I'm just wondering where to go from here. I think its still weak at long range tank hunting. But maybe that's something that Nids can't do?
-HQ-
Fyrant - Wings, Toxin Sacs, Bonesword, Whip (Hold in reserve and then comes in and assaults)
Tyrant - Heavy Venom Cannon, TL Devourers (Warlord. Tanks the middle and sits behind Aegis next to venomthrope for a 2+ cover save!)
Tyrant Guard x2
-Troop-
Genestealer Brood x5 + broodlord (infiltrates and horrors people and then joins an assault)
Termagants x15 - Devourer x5 (Screens for tyrant and hangs out midfield)
Hormagaunts x17 (Runs up with CC Fexes)
Warriors x3 - Deathspitters x2, Venom Cannon (Mans quadgun and holds home objective)
Warriors x3 - Devourers x2, Barbed Strangler (Filler synapse and skulks around and grabs other objectives)
-Elite-
Venomthrope x1 (Hides behind tyrant and does his thing)
-Fast Attack-
Sporeminds x6 (Deep strikes and makes the opponent go "oh crap")
-Heavy Support
Carnifex - 2 TL Devourers
Carnifex Brood x2 - Spinebanks, Bio-plasma, Adernal Glands
Exocrine
-Fortification-
Aegis Line with Quadgun
1850 points
59 Models
95 Wounds
That's a lot of wounds....
