SandWyrm here. Let's discuss shooting at a high level before we dive into the fine details.
In 40K, shooting is done in the following sequence:
- Roll To Hit
- Roll To Wound
- Opponent Rolls Saves
- Opponent Rolls Feel-No-Pain (if required)
Let's go through it step by step...
- First, the Guardsman has to hit the Marine. This is a
straightforward 4+ roll with no modifiers. So the probability at this point is 3 in 6, or
- To wound the Marine, the Guardsman will have to roll a 5+. But that 2
in 6 chance only comes if the Guardsman hit the Marine in the first
place. This roll is dependent on the last one; so the total odds of
wounding the Marine is, in reality, only 1 in 6.
- The Marine then gets his standard 3+ armor save. But again, this 4
in 6 chance only matters if the Marine has already been hit and wounded.
So the total contribution of the Marine's armor to his chances of
living or dying is only 4/36, or 1/9.
- This particular Marine then gets a Feel No Pain roll. Which, coming
after all the other dependent rolls, only offers 3/108ths of protection,
- So, the Marine's chances of dying from the lasgun shot are 1/36.
Yep. If the Guardsman had needed a 6 to hit and a 6 to wound with no save allowed, the average result would be the same. Exactly the same. So in terms of efficiency, we're only half as efficient as we could be.
Flames of War does it in this sequence. I'm not going to copy it, but it useful as a comparison.
- Roll To Hit
- Opponent Rolls Saves
- Roll Firepower To Destroy (if required)
Roll To Hit
Rolling to hit is based on the training of the target, and not the skill of the firer. So you'll always have a 2+, 3+, or 4+ base (conscript, trained, veteran) before modifiers are applied. The 3 modifiers in Flames are Long Range, Concealment, and Gone-To-Ground. Each of which is a one point penalty to hit. So it's actually possible for veteran infantry and tanks (whole army is same base) to be impossible to hit if they're hiding in some trees at long range.
Opponent Rolls Saves
Once you're hit, you roll saves. There are standard saves for infantry, guns, and unarmored vehicles. For infantry and trucks in the open, failing your save means you're dead.
For armored vehicles, the defender rolls a D6 and adds it to his armor value. If he beats the firing weapons's Armor-Penetration Value, then the tank is safe. If he doesn't, bad stuff can happen.
Roll Firepower To Destroy
This step is only required if you're shooting at dug-in infantry, or an armored vehicle. Each weapon has a firepower stat (usually 3+, 4+, or 5+) that you have to roll to actually kill the target. If you don't roll your firepower on dug-in infantry, they're fine. If you fail the roll on a vehicle, it will be bailed-out (stunned basically).
The Problems With The Flames Approach
Flames' approach isn't awful on the to-hit portion portion of the sequence, though it makes dug-in infantry a bit too durable. But it falls down with the armor-penetration and firepower steps. While hitting isn't that hard to figure out, the add-your-die-to-the-armor step just twists the brain, even after dozens of games. Especially when you're at long range and the penetration of the weapon is reduced by one. Then, depending on whether you glanced or penetrated that vehicle, the firepower roll will either bail or destroy the tank. While if you fail it, you have to remember whether the vehicle is safe or bailed out.
The M42 Approach
So we need detail on the to-hit end to efficiently use our die result range (for fewer rolls), but less detail on the to-kill end. We also need more ways to differentiate vehicles and weapons, because we're Sci-Fi and we need that capability.
I also want BOTH the attacker's skill and the target's skill to matter. To increase play speed (one of our stated goals) we should really have the attacker making all of the important rolls.
The rolls should also all use the same comparative chart, so that comparing one stat to another becomes automatic after a just few games. Particularly for veteran 40K players.
So here's what I'm thinking of for our sequence:
- Roll To Hit
- Roll Armor Penetration (if required)
- Roll To Kill
Roll To Hit
To determine your base to hit, take the target's Evasion (Ev) stat and add or subtract any modifiers based on long-range (+1), concealment (+1), gone-to-ground (+1), or Exposure (-1). Then compare the firer's BS to the target's Ev to determine what you need to hit. An 'a' means you hit automatically. An '-' means that you can't hit at all.
Roll Armor Penetration
This step will only be required for armored targets such as power-armored infantry, armored transports, and tanks. There will also be NO modifiers of any kind. It's a straight-up comparison of the weapon's penetration value with the target's armor value. If you make the roll, you've penetrated. There will be no 'Glancing' hits that work differently in terms of damage.
Roll To Kill
This step compares the Strength of the weapon to the target's toughness. Dug-in Infantry will get a +1 toughness. But that's the only modifier I have planned.
If the roll succeeds, the target is dead. If you've penetrated a vehicle, then failing this roll will still suppress them. Multiple suppression markers will have the following effects:
1 Marker = 'Shaken'
One of the vehicle's crew has been wounded. The vehicle may either shoot or move during it's next turn, but it may not do both.
2 Markers = 'Stunned'
The enemy has blinded the vehicle's sensors, or damaged the vehicle's tracks/engine. The vehicle may do nothing in it's next turn while it recovers.
3+ Markers = 'Bailed Out'
The Enemy's rounds have damaged the vehicle's ammunition stowage or fuel tanks. The crew has bailed out in anticipation of an explosion. The vehicle must make a leadership check at the end of the phase or be abandoned by it's crew.
You can think of a weapon's Strength stat as representing it's 'Explosive' strength, while it's penetration will be how well it goes through armor before exploding. That gives a lot of room for high-pen, low-str suppression weapons for tearing up vehicles. Low-pen, medium-str weapons for shooting up infantry, and the really big (expensive) boom guns that are good at both.
We'll have a suppression system for infantry as well, but I haven't worked out the details yet. Besides, this is enough to munch on. :)