You have weak anti-armor. The lascannon has a nice 66% chance of hitting, but it's only one gun. You're probably not going to see too much armor/high T units (ones with a high enough T to need an S10 weapon to deal with) in a 500 point match, but it's still a very real possibility (most people field at least a token piece of armor, simply because it requires a special counter to deal with).
The commissar's going to die if used on his own in frontline combat, because he's a high priority target. He might be tough as nails, but weight of fire means that statistically he'll be hit, receive wounds, and fail enough saves to be taken down. His strengths are mainly in shoring up other infantry units.
I'm also generally wary of putting too many options in a single unit, though I'm not sure how well founded this is.
I figured the Plasma weapons would work on the Armor as well. And I suppose the Commissar should just stick with his squads. Hmm.
Maybe I should cut back on the points used by the Commissar and Vet Squads, and invest in a heavy weapons squad. I'll play with that at work this afternoon, and put together another 500 pointer.
I also need to play with Vassal a bit. Don't want to be fumbling around with both the rules and the system when I actually play somebody.
Plasma works alright on light armor, but its main use is against heavy infantry (with a vet squad, each gun would have a 55% chance to kill a space marine (counting the 4+ to hit and the 2+ to wound, with no armor save because plasma is AP2) (and a 16% chance to kill the soldier with the gun)). Heavy weapon squads also need to be taken as part of an infantry platoon (which counts as a single troop choice). I personally recommend Vendettas, because for 35 points more than a lascannon squad would cost, you get three twin-linked lascannons (so three shots, each with a 75% chance to hit) and two heavy bolters, all in a nice 12/12/10 armor platform, that also happens to be a fast transport skimmer with the scouts special rule.
A single vendetta with heavy bolter sponsons would leave you with 150 points to spend on upgrading the lord commissar and veteran squads.
Also, on the difference between autocannons and heavy bolters, since they both cost the same but autocannons have the higher S: autocannons are useful against light and medium armor, as well as any enemy with T5 or above. Heavy bolters are the better choice for T4 and below.
At T5, an autocannon will inflict an average of 1.66 wounds per turn (adjusted for hitrate: 1.11 at BS4, .83 at BS3), minus any armor saves better than 4+. Heavy Bolters will inflict an average of 1.5 wounds per turn (adjusted for hitrate: 1 at BS4, .75 at BS3), minus and armor saves better than 4+. At T4, the autocannon still only inflicts an average of 1.66, but the heavy bolter climbs to 2.
Against an armor value of 10, an autocannon will score a glancing hit on a roll of 3, and a penetrating hit on 4+ (meaning .33 glancing hits, 1 penetrating, adjust for hitrates on your own, BS4 has a 66% chance to hit, BS3 has a 50%). A heavy bolter scores a glancing hit on a 5, and a penetrating hit on a 6 (.5 glancing, .5 penetrating). Against a value of 11, the autocannon scores a glancing on a 4, and a penetrating on a 5+ (.33 glancing, .66 penetrating), while the heavy bolter can score at best a glancing with a roll of 6 (.5 glancing, no penetrating). An autocannon can still inflict damage at a value of 12, glancing on a 5, and penetrating on a 6 (.32 penetrating, .32 glancing). I don't recall any values of 13, and at 14 an autocannon can't even inflict a glancing blow.
want to play but really? 90 bucks for the starter set?
Search 4chan's /rs/ board for "vassal". The things you want are "Vassal 40k.rar" and the tyranids 5th extension, which adds counters for the new units.
Sadly, I can't tell you here where to find scans of the rulebooks and codexes, but they're just about everywhere, if you know where to look.
i want to do this legally and with no 4chan, thanks.
Vassal 40k is legal. It's called fair fucking use. The project was illegally shut down with harassing cease and desist letters from GW, which the creators, despite being in the right, could not fight due to the exorbitant costs of legal counsel. Sadly, there's no penalty for such things, since then rich corporations would actually have to exercise caution and restraint to stay within the bounds of the law, instead of rampaging about with flamboyantly anti-social bullshit like this.