I've never been happy with the damage rules for WH40K RPG's. The way you just roll a fistful of dice directly for damage has never sat well with me. It doesn't match up with the main Warhammer 40K wargame rules. This is my version:

Instead of every weapon having its own unique damage, weapons have a Strength value which determines how much damage they do .

Whenever a character is hit they make an opposed Toughness test against the Strength of the hit. If the test is failed then 1D10 damage is inflicted, with +1 damage to the roll for each degree of failure. Some weapons may have this damage roll modified. This damage is reduced by armour in the normal way.

Wounds no longer soak damage. Instead when a character takes damage they roll directly on the Critical Damage tables and apply the result. They ALSO deduct the damage taken from their wounds total. If a character 's wounds value is reduced to 0 they collapse unconscious in the same way as for fatigue. Once they come round they have 1 wound and take 1 level of fatigue. If a character is bleeding when they fall unconscious they die of blood loss.

Gamebook said:

One or two issues, though some might be fixable with some scaling/tweaking.

First off - I'd assume penetration is still present at the current values (no changes to armour values, so no changes to penetration needed)? If not, bolters become just as lethal as lascannons.

Secondly, in the basic game, you don't "roll on the Critical Damage table", you build up critical damage over time and apply the effect from the table. Rolling directly means a 20% chance of death everytime you take damage (30% for the head). This is suitable only for a seriously "gritty" campaign - something where you want being shot to be a really big deal. It'd work for modern day spy or low-action crime RPGs, but it will probably result in masses of rerolled characters and a massive recruitment drive being needed by the Ordos Xenos.

Thirdly - what sort of Toughness test/Strength values are we talking about? Should it be reasonably easy to pass (therefore they ignore most hits) or more challenging (in which case they'd be taking a lot of chances at death via the critical tables)?

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Basically the original system takes the Strength vs Toughness part and makes it a "one cancels the other" - if you're stronger than they are tough, you deal more damage. Also bear in mind that the errata dramatically changes the damage values for a lot of common weapons (mostly bolt weapons) which changes the dynamic considerably (i.e. Heavy Bolter is no longer the ultimate weapon).

Regarding Critical Injuries and rolling directly on them, perhaps you might take a page from GW's Inquisitor RPG (free PDF rulebook available on their website ), where a character's toughness did not actually confer immunity to damage, but instead served as a "buffer" between injury levels. For example, if a las round gets through your armour, you already know you will get hurt - all that's left to determine is how much. It is what I'd deem a superior representation of a Space Marine's toughness in that they can still be harmed by a constant barrage of small arms fire - they just take a lot more shots to go down than the average human .. instead of simply shrugging them off with zero effect on the body.

To combine this with your idea, you could remove wounds/hitpoints altogether and instead add Toughness as "buffer points" between the Critical Injury levels. When an attack punches through a character's armour, you roll for the Crit Table, but take Toughness soak into account. The end result determines the injury received. Buffer points are not recorded, they only affect how much damage is needed to jump from one injury level to another. Accordingly, when a character is injured again at the same location, damage allocation begins at the next Critical Injury following the one triggered last, not any hypothetical buffer points left over from the last attack.

It makes combat somewhat more deadly in general, whilst at the same time minimising the risk of one-hit kills: provided an unarmoured and uninjured Space Marine with TB 8 receives an injury under this system, it would take 82 points of damage to knock him to the "10" result on the Crit Table - which is more than the AP + TB + Wounds under the standard rules. Death only becomes ever more likely as the Marines accrue more and more injuries across their body as the battle progresses.

As an added bonus, this solution would also make lasting, severe injuries requiring cybernetic replacements more likely, rather than only providing that small window of ~5 points of damage between "nothing happened" and "he's dead, Jim" on the Crit table.

To answer some queries.

Penetration and armour values are slightly higher across the board. Lasguns and autoguns I've given a penetration of 2, to differentiate them more from laspistols and autopistols which still have 0 penetration. In real life assault rifles are much better at punching through body armour than pistols. Marine power armour is now 12 on the body and 10 on the limbs/head though to counteract this.

Armour and cover makes a drastic difference to survivability since damage is now only ever rolled on a single D10. Power armour can reduce the roll by -8 or more for many hits. If the roll is reduced to 0 or below by armour then no damage effect is applied at all. A marine would have to make a really bad set of dice rolls to take serious damage from a lasgun, or any damage at all. A lascannon beam hit is very likely death, but that has always been the case in all 40K rule systems.

A lasgun is an average Strength weapon, under my system it has a Strength of 50. When used to shoot an ordinary Toughness 30 unarmoured human it has about a 50% chance to disable or kill them on a hit. Marines under my system have a Toughness of at least 60 (I have abolished Unnatural Toughness). Other weapons have proportional values, from boltguns at Strength 75 to lascannons at Strength 140.

This system is indeed brutal, with a chance of dying to every hit. Small arms fire is not particularly dangerous to a marine though, and Fate can be used as well.