Should I fire frag or krak grenades?

[Rogue]

I'm not keen on weapons with options. I always end up worrying that I've made the wrong choice. Case in point: the grenade launcher. Should I fire frag or krak grenades? One gets me more goes with a worse grenade, the other gets me a single shot that might actually do something.

Fortunately, this is one of those things that we can have a fair crack at with the math-hammer. And here it is.


Frag vs Krak, chance to cause a wounding hit


Frag vs Krak, giving Krak a flat 2 damage to approximate a d3

Each chart shows a comparison of toughness and save (toughness down the side, save along the top). Where they meet, the number in the box represents the number of frags you'd need to fire to achieve the same chance of causing damage as a krak grenade. If the box says 2, for example, then 2 frags will achieve the same as a single krak. For the grid on the left, if the box is green, they'll do slightly better; if it's yellow, they do exactly the same.

But the right-hand grid is the more useful one. Here, a green box suggests that frag is the better option; yellow, that frag and krak are balanced; red suggests going with krak; and grey indicates that even 6 frags will be worse than a krak (statistically speaking). My thinking here goes like this:

If you only need two frags to match the krak, go frag. At three frags, we have a 2/3 chance of doing better with frag, so go frag. Four frags is the critical point. If four frags will do slightly better than a krak, it's a toss up - half the time, frag will be worse; half the time it'll be better. So you might as well go with your personal preference. But if four frags exactly match a krak, then go krak - now you have a 50% chance of doing worse with frag (rolling 1-3 shots), and only a 33% chance of doing better (rolling 5-6 shots). And once you need five or six frags, stick with the krak.

Curiously, looking at the upper grid (which is only concerned about causing damage of any kind), frag comes out ahead in almost every case. Krak is only the better choice against a 2+ save (if the target is toughness 4 or higher), and against toughness 6 (if the save is 4+ or better) - toughness 6 is krak's comparative sweet-spot, where it's still wounding on 4s but frag has dropped to 6s. So in most cases, if we're just looking to cause single wounds, frag is the way to go.

However, when we switch to the lower grid, there's a significant shift. On this grid, I've doubled the damage output of the krak grenade to represent its better damage characteristic - I've averaged it at 2 (rather than d3) to make life easier, but it does mean that this is something of an abstraction. In some cases (such as single-wound targets), this extra damage is wasted, but sometimes it matters (primaris are apparently quite popular). Broadly, this doubles the number of frags required (with rounding accounting for the appearance of odd numbers here). Suddenly, the weighting shifts heavily in favour of the krak grenade. Now, frag is only the better choice against toughness 1 (unless the save is 2+), and toughness 2 (if the save is 6+ or worse), and that's a ridiculously limited choice of targets - in practical terms, if we want to maximise damage, we should always choose krak.

Short version: if you're going after one wound models and want to spread damage around, use frag; if you want to inflict multiple damage on targets, go krak.

I know that sounds obvious, but the bit that surprised me was how universally that applies, especially with frag, In my head, frag is for low toughness, lightly-armoured targets. But the numbers suggest that, very limited scenarios aside, frag is the better option for single wounds, even against toughness 7 or higher. Or to look at it another way - the factor that primarily determines the grenade you should use isn't toughness, or save - it's the number of wounds on the target.

[There are more moving parts in this one, so I'm very open to argument.]

[And I have no idea how to make those opening images any bigger. Sorry.]

Edited July 7, 2020 by WarriorFish
Larger images added

[Rogue]

Thanks, WarriorFish.

 

Because I already had the spreadsheet set up from before, I've also run frag missiles vs krak missiles. There are similarities - krak is still twice as strong as frag (just at 8 and 4 with missiles, compared to 6 and 3 with grenades), but krak missiles also have better AP and damage than their grenade counterparts, coming in at AP-2 and damage d6 (in both cases, double what a krak grenade puts out). Frag missiles don't gain any AP or damage increases, so we might expect the gap between the two to be wider than with grenades.

 

We also need to extend the toughness range up to 9 - T9 is sufficient for comparison purposes, because from this point forward, the S4 frag will always wound on 6s and the S8 krak will be on 3s until T16, so the damage ratio isn't going to change.

 

Here are the tables:

 

Frag vs Krak, chance to cause a wounding hit

 

Frag vs Krak, giving Krak a flat 3.5 damage to approximate a d6

 

The tables roughly track the ones for the grenades - frag is usually better if you just need to spread wounds around; krak if you want to put a lot of damage on something.

 

The interesting bit is the scale of the difference. There's almost no scenario in which frag missiles cause more damage than krak - unless the target is toughness 1 or 2, with no save, you're better off just putting krak into it. And with the increasing number of multi-wound models around, or even single-wound models with various forms of FNP (where causing multiple damage is helpful), krak doubles up as a pretty effective anti-heavy-infantry option.

 

When it comes to mowing down single wound models, the frag missile is far more useful, but not as automatic a choice as the frag grenade. Against anything T4 or less, frag is the better (or evens) option (except for T4 with a 2+ save). And against anything with a 4+ save or worse, frag is better or evens (except for T8). As with the grenades, the bit that surprises me is that frag is a good option even against T9 targets if their save is 4+ or worse. In fact, outside of the infrequently occurring T1 and T2, the main determining factor here is the save: lighter armour matters more then how tough the wearer is.

 

Two notes to finish with.

 

Firstly, these tables are approximations. Krak doesn't do 3.5 damage a time. Knowing that a frag is more likely to do well in a given scenario doesn't stop you rolling a 1 for shots. But it should balance over time, as with most things 40k. The lower the number in the box, the more likely that frag out-performs krak, but the key word is likely.

 

Secondly, against any target with at least 6 wounds, krak is always best. Why? because the d6 shots of frag and the d6 damage of krak cancel each other out (as does the to hit roll). The superior statline of the krak missile will then always come to the fore (except for the tiny number of cases where we have a 6 wound target with a toughness of two or less and no save, but even then krak is no worse than frag). I know that's just saying 'Fire anti-tank missiles at tanks', but I like the maths - d6 is a variable, but as such it can still cancel with another, equal variable, leaving a much simpler calculation.