Forum:Grenade (mod) Power - Arbitrary or meaningful?

Wandered into Old Haven with my Playthrough 2 Hunter. Got 835 health (Lvl50) and a 1286 shield. Some bastard Lance Marine chucks a contact grenade (which exploded five yards to the left of me I might add) and I'm down to 20-30 health. It's happened before but I happened to pick up the grenade mod after I turned him into a shuddering stick of lightning and noted that the mod rating was 120. Which I would guess is generally considered to be more powerful than, say, a 101, and less so than a 137.

But after that I'm lost. If I have a weapon with a damage rating of 200, I would expect to deal 200 (+ the character's proficiency amplifier for that weapon type) points worth of damage on a non-critical hit.

So what relation does that 120 rating have to the actual damage doled out by a grenade? Is there a relation or is the power of grenades solely measured to necessitate me running away and cringing behind cover while I slap on a Panacea and a Survivor COM just to ensure I don't die from stubbing a toe?