I like the pretty colors. And I messed up on some of the calculations of course (I was just kinda estimating in my head), but trying to subtract the average value doesn't really mean much. The dice only explode for PCs and important people, so it really isn't relevant unless we decide to betray each other for some reason or are in a "boss fight".
Maybe calculating the average damage taken in each armor would show it better?
It does require some more math, so correct me if I am wrong. While its easier to estimate the average of 1d10 by making it five, it is *technically* 5.5 (1+2+3+4+5+6+7+8+9+10)/10. Using this, we can probably get an idea of what the average damage would be in all cases. I'm keeping your color scheme, and am horrible at math, so brace yourself

.
Autogun 1d10+4 vs:
Light armor average damage: ((0+1+2+3+4+5+6+7+8+9)/10= 4.5Carapace armor average damage: (1+2+3+4+5)/10= 1.5Heavy armor dude average damage: (0*10)/10=0Spear thrust 1d10+3 (or +2 or +4 or however strong they are, I went with three because it "felt right" for some low life scum and it makes the numbers perfect) primitive vs:
Light armor average damage: 1.5Carapace average damage: 0Heavy stubber 1d10+5 3 pen vs:
Light Armor average damage: (4+5+6+7+8+9+10+11+12+13)/10=8.5Carapace armor average damage: 4.5.Heavy armor dude average damage: (1+2+3+4)/10=1 Does that make things a bit more clear? And not covering the head isn't a *big* issue, it would be imperative for him to get a helmet if he gets in a bunch of gunfights, but called shots are -20 (with that little armor, he *might* actually be safer if people actively aimed at his head) , with only a 10% chance to get hit there otherwise.
Done
Went with a multi-melta rather than a lascannon.
Better against groups with blast(1) and semi-auto, even if it has shorter range and 4d10+5 vs 5d10+10, but still pretty potent against tough stuff with the three-shot burst.
Its not actually semi-auto, that was a typo fixed in the errata

. Plus you can only start with weapons you have the skill for, and you *don't* have the skill for heavy weapons. (PG 272, under Acquisition and Starting Characters, second bullet-point.)