So anyway, 8th edition has changed that. Both due to the weapon profile and the rules.
So viable, in fact, I went ahead and bought a box of nobs so I can make a big choppa nob for each of my 6 units of boys!
|1 Goff, 2 Evil Sunz, 3 Blood Axe.|
Let's examine the difference.
Big Choppa: S+2 (so S7), AP-1, 2 damage you'll notice this is essentially the same as a Deffgun
Power KLaw Sx2 (so S10), AP-3, D3 damage, -1 to hit.
Big Choppa is also 36% of the points. If I take 3 units of boys, that's a savings of 48points!
The 3 categories:
Strength: When is S10 better than S7? Anything T5 or lower. Then you're wounding on 2+ Also anything with T20 or higher - which does not exist. But once you get to vehicles you're still at a 3+, and thus have no benefit over S7.
AP: -3 vs -1. That means you have a much better chance of getting that damage through, but having any AP at all makes the Big Choppa usable. Taking a 3+ to a 4+ is pretty nice.
Damage: D3 vs 2. Even if you do get the PK through, there is a 1/3 chance you'll only do 1 damage.
Let's do some mathhammer:
Vs a Space Marine (T4, 3+ save, 1W)
BC: 3A * (2/3 chance to hit) * (2/3 chance to wound) * (1/2 chance to not save) = .667 dead marine
Points/damage =13pts per dead marine
PK: 3A * (1/2 chance to hit) * (5/6 chance to wound) * (5/6 chance to not save) = 1.04 dead marine
Points/damage=24pts per dead marine
Vs an average vehicle (T7, 3+ save, multiple wounds)
BC: 3A * (2/3 chance to hit) * (1/2 chance to wound) * (1/2 chance to not save) * (2 damage) = 1 wound
PK: 3A * (1/2 chance to hit) * (2/3 chance to wound) * (5/6 chance to not save) * d3 wounds = 1.66 wounds
So as we can see here the big choppa is statistically more points efficient, and by that I mean you pay fewer points for equivalent damage. That's not a bad deal at all.