Blast weapons and scatter

29 April 2009 | 5th Edition

With the game mechanics for blast weapons, Devastator Squads with multiple plasma cannons or missile launchers (frag missiles) look very impressive. Let's have a look why.

First thing to say here is that technically blast weapons can never miss (provided they are in range in the first place). Yes they can scatter but that is a bit different. In fact every blast weapon has exactly the same 33% or 1/3 chance to get a direct hit without scattering — and that includes your Ork hordes at BS2 who traditionally can't hit the proverbial barn door. Look at your scatter dice, it has six faces, of which two are 'HITS' and every blast-weaponed firer throws that same dice.

On the face of it it would seem then that blast weapons are a poor choice for higher Ballistic Skill (BS) models as they gain no real benefit. You'd be right. Up to a point, because what separates the Orks from the Marines here is the effects of scatter and this is where things get very interesting.

The scatter dice and the dreaded arrow

If the scatter dice rolled at average allows you a 1/3 chance of a hit what affects will scatter have? Remember that if any portion of a target model's base is caught under the blast marker then it still counts as being hit. This renders scatter slightly less of a disadvantage provided you are firing at a largish unit spread out to maximum coherency as the chances are good of catching something under the marker — even if it isn't what you initially aimed at. Yes if you're really unlucky in your rolls by rolling high then just hope the shot scatters onto another unit.

I thought it might be useful to show in table form the various scatter distances in inches for various Ballistic Skills. Using the game scatter mechanic of 2D6 minus the BS of the firer we get the following results.

The average scatter distance is arrived at by taking average score of a 2D6 result (which is 7") then minusing the BS of the firer.

Scatter distances
BS	Min scatter distance	Max scatter distance	Average scatter distance
0	0	12	7
1	0	11	6
2	0	10	5
3	0	9	4
4	0	8	3
5	0	7	2
6	0	6	1

Obviously the minimal scatter in all cases will be 0".

We can see that the better the BS results in less the scatter thus reflecting the better skill of the firer. In terms of Space Marines (mostly BS4), it means a model with a plasma cannon will average a 3" scatter, which isn't so bad. Sammael (BS5) will average just 2" scatter, but even his max of 7" scatter isn't a disaster if he was firing at a large unit of models and if the central hole of the marker was placed in (roughly) the centre of the target unit.

This also leads to an interesting phenomenon: that of firers with lower BS have a weapon with potentially longer range then models with a higher BS, as shots that scatter beyond the weapon's normal range still count. This could be a great advantage to them if they are firing at multiple units tightly castled up together within a small table footprint.

Is scatter so bad?

It's always better to hit obviously, but consider that when you move a marker in any given scatter direction you measure from its centre — so some part of the body of the marker when moved might well still be over the area of what was the centre of the marker when originally placed. Sounds complicated? Not really. Simply put it means that effectively the marker is potentially still covering the original target: i.e. scatter distance minus the radius of the marker gives the true extent of its scatter.

Effective scatter using the small blast marker

Here are the real scatter results when firing the small 3" blast marker with average scatter of 7", minus the marker radius of xxx", and showing the distance of the marker edge from the original centre point aimed at:

Scatter distances with small blast marker
BS	Max scatter distance	Average scatter distance	Distance of marker edge from original marker centre
0	12	7	5.5
1	11	6	4.5
2	10	5	3.5
3	9	4	2.5
4	8	3	1.5
5	7	2	0.5
6	6	1	-1.5 (remains over target)

So we can see that Sammy's BS5 plasma cannon has become even more accurate and that our BS4 Marine with his plasma cannon will stand a pretty good chance of hitting a target unit when rolling averages on 2D6.

Effective scatter using the large blast marker

Here are the revised scatter results when firing the large 5" blast marker with average scatter of 7", minus the radius of 2.5", and showing the distance of the marker edge from the original centre point aimed at:

Scatter distances with large blast marker
BS	Min scatter distance	Average scatter distance	Distance of marker edge from original marker centre
0	12	7	4.5
1	11	6	3.5
2	10	5	2.5
3	9	4	1.5
4	8	3	0.5
5	7	2	-0.5 (remains over target)
6	6	1	-1.5 (remains over target)

This makes Space Marine weapons like demolisher cannons and whirlwind missiles even more deadly, and of course any ordnance coming inwards from something like Imperial Guard (BS3) will scatter only on average 4" with the blast marker edge only 1.5" away from the original target point. It's a sobering thought if you have a large marine unit under that lot.

Now, we could have even more fun here and take the base sizes of target models into consideration, but no, that will be for: Blast weapons and scatter II.