Well, I kinda went a different direction a bit...
C5-9 "Cripplestrike" Lasgun
Class: Basic; Range: 90m; RoF: S/3/- ; Dam 1d10+3E; Pen 0; Clip 40; Rld Half;
Special: Crippling (2), Accurate, Reliable
So I threw together a few from the Ranged Weapon table, as well as the General Eq. table. At the same time I was more concerned about working out design versus trait-balance
From Gen Eq:
Durable: when the undergoes destructive damage, 6+ on a d10 means its okay
Capricious: whenever used for a test roll d10, on a 1, it imposes a -10 penalty
From the Ranged:
Rapid Clip Eject: half-round for reload
Crippling Munitions: Cripple (2)
Incredibly Lethal: Accurate
4 stacks of Small Clip (feel free to tell me if that's BS)
Rare Model: -20 on acquisition attempts outside of place of manufacture
Found within a STC fragment located on a moon in [home system] the Cripplestrike, or "Five-by-Nine" harnesses a modification in the firing chamber to produce a nanometers-wide gap within the center of the beam produced during firing. Within this microscopic gap, energy from the beam arcs around and produces an area of intense electromagnetic radiation. when it comes into contact with a surface, the radiation sinks deep into organic tissue and scrambles electrical systems, the force of the radiation expanding upon contact also leaves uncharacteristically circular scorch marks averaging 2-5cm in diameter, giving rise to the "Halo-strike" Las.
Commonly used by Light Infantry and Regiments particularly skilled in hit-and-run tactics and guerrilla warfare, they pack a punch, but have less punches to throw. The discharge also is documented to have minor effects on accuracy, as the energy sometimes leaks through the grounding and into the user's hands. Specialists from [player character's regiment] who train for years extensively with these weapons undergo a single shot from a Cripplestrike at 10m to prove their dedication, and are commonly addressed as "Crips" in Low Gothic
So, yeah, my only balancing was to knock 1/3 of the clip off and give it a 10% chance of -10 penalty...
but the clip restrictions make sense in canceling out the Rapid Eject. and partially the Cripple, then I figure Capricious more-or-less covers the rest to a pretty good degree. And the Rare Model is a pretty good tool for playing up the value of the weapon, and allows me to give PCs a reason to interact with other Regiments ("Oh, hey, we're from the same system-- Why, yes, in fact, we *do* have some fresh gear!")
Unfortunately I didn't have a completely fluff-solid reason for the Mechanicus to have beef with the design, other than making it the product of a *corrupted* STC frag, and I reeeeaally don't want to go there... (If I did, I'd also feel obligated to throw in Corrupted Pattern, and I don't want to do that to my PCs)
Plus, I figured some of the more civilized reg.s will give the PCs issues over how "barbaric" the ritual maiming of their Sharpshooter's is. (I've got a running adv. specialization variant of Sharpshooter, so it ties in well)
I was also considering giving it Valuable (+20 for Commerce tests when trading) but I figured that that would be reserved for less available equipment.
All-in-all, do tell me if you think that I went too easy on the balance with this. I know I went a little more in the PCs favor, but it has to be a weapon they'll find fun and effective. I figure I leave the harsh-reality stuff to scenarios and killing off a few more Comrades than I usually would.