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During my last game vs Necrons I used a unit of Dev Centurions ML/2xlinkedLAS and a GravCannon and GravAmp. Im thinking of dropping the GravCannnon

With tank hunter in effect from IF tactics I felt that the GravCannon wasnt as effective as another ML/Las would have been.

With a grav cannon yes you get 5 shots, but you have to hit 6's (with re-rolls) regardless of the vehicles armor value and you HAVE to get 2 6s to wreck a vehicle,

the ML/Las gives you 2 shots(re rolls on the las) far better odds on rolling a pen - especially with low armored vehicles. then you also get re rolls on the damage table. And the +1 (+2 for LAS) on the damage table result when using IF tactics.

Are gravCannons really worth it for vehicles? especially when using IF tactics?

Of course they are worth it but not as IF and not if only one has them.
For IF i would go all Lascannons and for other chapters the best setup would be 3 cannons or 3 cannons and one lascannon if we are talking bout 4 man squad

First off, including the ML when debating LC vs GC is pointless as you can take a ML either way. Also you only get +1 on the damage table against buildings with the IF CT and Tank hunters is a reroll on the AP roll not the damage result table.

Against an any 3 HP vehicle the GC with amp has a ~27% to wreck. 3 GCs with amps have ~84% chance of wrecking.

A TLLC with tank hunters has ~28.8% of exploding an AV 10 vehicle. 3 TLLCs with tank hunters has ~89% chance of destroying an AV 10 vehicle.

So trading a GC for a TLLC only nets you a ~5% bump against the worst vehicle AV at the expense of great anti-MC, anti-heavy infantry fire power. Also the GC is better against higher AVs and vehicles with cover saves (as volume of fire is better). Though range could be a factor.

 Tarrasq wrote:

A TLLC with tank hunters has ~28.8% of exploding an AV 10 vehicle. 3 TLLCs with tank hunters has ~89% chance of destroying an AV 10 vehicle.

Sorry your math isn't quite right. Its a 63.9% chance of destroying with 3 shots, not 89 - assuming your original 28.8% chance from one shot is accurate.
(1-0.288) * (1-0.288) * (1-0.288) = 0.361
1-0.361 = 0.639

edit: Apologies, my mistake. I misread destroyed/exploded a couple times.

 Dracos wrote:


Sorry your math isn't quite right. Its a 63.9% chance of destroying with 3 shots, not 89 - assuming your original 28.8% chance from one shot is accurate.
(1-0.288) * (1-0.288) * (1-0.288) = 0.361
1-0.361 = 0.639

The problem is systematic - your other calculations fall into similar traps.

Well when you fail to account for the significant chance for 3 TLLCs to wreck (strip HPs) an AV 10 vehicle of course you're going to come up with the wrong number, Dracos.

In fact I shorted the 3 TLLC a bit because I didnt include the chance to double immobilize. Which brings it to ~89.8% to destroy.

You did not say destroying, you said exploding - which is what I assume the 28.8% chance happens to be. Dracos is correct in the exploding calculation - which is what you claimed the 89% chance was.

Either way, it is a common mistake to simply add together probabilities.

Dracos calculation determines the chance to NOT explode the vehicle and since the results explode/do not explode are collectively exhaustive, subtracts it from 1.

 Tarrasq wrote:
First off, including the ML when debating LC vs GC is pointless as you can take a ML either way. Also you only get +1 on the damage table against buildings with the IF CT and Tank hunters is a reroll on the AP roll not the damage result table.

Against an any 3 HP vehicle the GC with amp has a ~27% to wreck. 3 GCs with amps have ~84% chance of wrecking.

A TLLC with tank hunters has ~28.8% of exploding an AV 10 vehicle. 3 TLLCs with tank hunters has ~89% chance of destroying an AV 10 vehicle.

So trading a GC for a TLLC only nets you a ~5% bump against the worst vehicle AV at the expense of great anti-MC, anti-heavy infantry fire power. Also the GC is better against higher AVs and vehicles with cover saves (as volume of fire is better). Though range could be a factor.

The HUGE problem is the 24" range of the Grav Cannons. With that range, you're likely only gonna get one good turn of shooting with the Centurions. Afterwards, any low Ap the enemy has will be turned right on them, and with no invuln save and so many ways to remove cover now, I don't they will survive.

TLLC on the on the other hand, can be camped on the other side of the board, and anything the enemy sends to attack them won't be hurting much else since they'll probably be so far away from other units.

 calypso2ts wrote:
You did not say destroying, you said exploding - which is what I assume the 28.8% chance happens to be. Dracos is correct in the exploding calculation - which is what you claimed the 89% chance was.

Either way, it is a common mistake to simply add together probabilities.

Dracos calculation determines the chance to NOT explode the vehicle and since the results explode/do not explode are collectively exhaustive, subtracts it from 1.

Apparently someone else forgot how to read...

Yes the 28.8% chance is the chance for the TLLC getting the explodes result as I was comparing the chances of each gun by itself to destroy a vehicle, and as it happens a single shot TLLC can only destroy by rolling an explodes result. However and I'll quote myself

3 TLLCs with tank hunters has ~89% chance of destroying an AV 10 vehicle.

Notice how the bolded does not claim the chance of exploding a vehicle?

Ferrum_Sanguinis wrote:The HUGE problem is the 24" range of the Grav Cannons. With that range, you're likely only gonna get one good turn of shooting with the Centurions. Afterwards, any low Ap the enemy has will be turned right on them, and with no invuln save and so many ways to remove cover now, I don't they will survive.

TLLC on the on the other hand, can be camped on the other side of the board, and anything the enemy sends to attack them won't be hurting much else since they'll probably be so far away from other units.

It's true that you can sit in the backfield with TLLC Centurion however the firepower a TLLC Centurion puts out is easily overshadowed by the gravcannon and the types of guns that are good at taking out centurions just so happen to have long ranges too. So you might as well be up close maximizing firepower. Besides these are the same things I've heard about the wraithknight, however many lists seem to do well with them in it.