coil-gun? *facepalm* ah, freck... I knew there were still some weapons I hadn't tried yet!
It's not in 2.2.1, but in 2.3, the coilgun is a researchable sniper weapon, based off the electromagnetic rifle (AKA Bolter), and alien Needler weapons. It's ammo capacity blows immense chunks (only 2 shots per clip, and the clips are 2x2 objects), but it does a ridiculous amount of damage over stupefyingly long range, without the inaccuracy issues of the bolter.
Like the UFOpaedia entry says, "we basically scaled down a tank's main gun."
Name: Laser Artillery
Long range support weapon. Built upon upscaled heavy laser, this weapon can deliver specially developed HEAP or HEI 30 mm shells over long distance with high accuracy, serving as field artillery as well as another kind of "sniper". Not much improvement over HPML in damage, but laser propulsion allows semi-automatic operation, and holographic targeting increases accuracy. Its greatest disadvatage is that, after certain distance is travelled, laser loses contact with projectile, resulting in high gravity drop after certain point, limiting maximum range.
Since standard DF cartridges won't be sufficent to power this laser, each ammo pack contains a larger DF pack.
Stats:
Damage type-explosive
damage: 135 HEAP, 110 HEI
accuracy: 0.7 aimed shot, 1 for 3-round burst.
Range: 120
Clip size: 3
TU cost: Aimed shot 19, burst 28.
I'm kinda leery of this weapon, mainly because of the TU cost. If I'm reading you right, it does a total of 245 damage, for 19 TU. The only weapon that compares with that kind of damage on a single shot is the Unrestricted Blast mode of the Particle Beam Cannon, which does 210 damage, has a blast radius, drains the entire 8-shot clip, and costs 28 TU.
Even the Coilgun's Aimed Shot only does 180 damage for 18 TU, which is the closest direct comparison, and even then, it's not the primary fire mode of the weapon (the primary fire mode is Snap Shot; 12 TU, same damage, but 1.5 accuracy). Further, the Coilgun's lowest accuracy is only 0.9, and does the same 180 damage as its snap shot. I'm thinking your weapon idea might be a bit overkill; too TU-intensive to use effectively, too much damage to keep it from being gamebreaking if you can overcome the TU-cost. And this is a
laser-based weapon. From a research standpoint, having a weapon that strong available early might be gamebreaking; it might be enough to dissuade people from researching Particle Beam or Needler weapons entirely.