A few weeks ago my group started on the adventure from the main rule book. and got to the part where they are attacked by a hexalid, which in my mind is a massive reptile easily twice the size of a man. The guardsman was bitten , picked up and shaked around like a rag doll and then something occured to me.

The guardsman has TB3 and 5 armour points( doubled to 10 cos the bite is a primative attack) total = 13

The Hexalid has 1d10+4 damage for a max of 14 (i think)

So I have to roll a 10 to injure him.

Maybe it's just me but this sounds wrong. The beast is meant to injure 1 or more of the group according to the crow-fathers plans but it seems that all it is going to do is scratch some armour.

Any thoughts?

The Hexalid does a d10+6 damage, but yes, imperial guard flak armour will be hard for it to punch through. I dont see much of a problem though, Unless everyone in the group is fully armoured, just have it jump one of the tastier and less protected characters. Also it can use grapple to inflict fatigue to try knock the guardsman out. The crow father intends to try to kill or maim as many as possible with its creature but its working with what resources its got. It didnt expect the players arriving, and most likely didnt expect them to be armoured, so it throws what it can in their way. If it could give its maddened creatures man-stopper rounds it probebly would. And remember that the encounter isnt intended to wipe out the group, just hurt it and shake it up. Finally, it causes fear, which allways buffs up a creatures lethality. If you really want the Hexalid to hurt more I suggest that you count its 10+6 damage as before S bonus and then add an extra +5 from its 50 strength, but it might just get a bit to tough then.

Exact same thing happened to our group, thing attacked the Guardsmen who then went down, then we reallised it was primitive and he had taken no damage so we just said he played dead >.> while the rest of us killed it.

I'm currently running the hexalid battle in a play by post game. Seeing as the acolytes are all rank 3 and rather adept at gunning down anything that gets in their way I've buffed it a bit - it's got 30 wounds instead of 20 and once it grapples a target it inflicts damage with it's tongue every turn and can also rake the victim with it's front claws. It can also fling those grappled aside, which combined with the narrow strip of level ground the acolytes are on should make for an interesting point.

On topic - the hexalid is about to attack the feral guardsman this turn, who'll be able to deduct 12 damage from each hit. So I figure if it can knock him down it can scrapple atop him and rake him with four of it's legs at once, which should put some fear into the acolytes. Or maybe it'll just try and grapple his head and draw it into it's maw.

Yep, "primitive" beasts have a REALLY hard time against modern battlefield armour.

Some things that come to my mind/used by me:

Special ways of attacks:
The combatsystem for most rpg systems is build for "humanoid against humanoid". That is not the way a predator would attack. If a grizzly bear grapples with you, he is going to bite the same time AND his claw have a good chance of scratching. If a panther or lion is after you, he will go for the neck and will have less problems since nature specially build him for this mode of attack. Custome design; tried and true by over a century of evolution. To reflect this, I give predators some "special rules" like "every melee attack with three levels of success (after dodge) counts as an attack to [body location]" to better the show the difference in their fighting and to give them chances to go for unarmoured/less armoured spots.

On the other hand, keep in mind that a lot of wild beast go for a grapple as part of their combat. While clawing and biting. To reflect this, every round of grappling will make the human (pc) suffer the creatures damage. Men do not go wrestling against a bengal tiger or kodiak bear.

Add some combat talents:
I do not have my rolebook at hand, but I know there are lots´s of combat talents that add some extra damage. If the beast is considerable big/vicious I would normally add some of the talents... just to make sure the players do not scoff at it & to make the encounter/fight interesting & intense.

Re-consider the armour rules:
I am not quiet "by-the-book" when it comes to the "primitiv quality rule" for armour. A modern ballistic west is good against bullets. Really good. It is not so good against an old fashioned bowie knife. So I do not double the AP of non-rigid modern armour. But in the case of your example... I assume the armour to be "rigid".

Hope you find the input to be helpfull