This is what i had in mind when i drew the PBC-30h, i was limited by PMG though.
The PBC-30h, if you haven't seen the original PMG version, is a Plasma Bolt Cannon. It shoots rods of hot charged plasma that are devastating to armor, not because of their speed or penetration power, but because they tend to melt the target or set the target aflame. Its completely recoilless
It comes in two models. The top is a model issued to soldiers sporting medium weight power suits or emplaced positions, weighing roughly 26 pounds it features a high pressure gas reserve and a jack that plugs into the soldiers power supply. The barrel is shortened reduce the amount of energy drained so the soldier's suit can still function reasonably well while the weapon is firing. When set up in an emplaced position, the weapon will be hooked up to a reliable power source and can be shot for surprisingly long amounts of time without over heating, up to a minute, without any adverse effects on future performance. The second model is for lightly power-armored soldiers or soldiers not using power armor. It uses magazines with 40 capsules in them containing enough gas and power for 1 bullet, essentially a 40 round magazine. Light power armor suits cant put out enough power to utilize this weapon and maintain mobility at the same time, so magazines are necessary. Soldiers using this weapon without a power source should definitely have a defensive role, as its bulk will be slowing the soldier down, 26 pounds gets HEAVY after a while.
The way it works is actually plausible too, seeing as you have enough energy. Superheated and ionized gas is molded into rods as it passes down the two magnetic rails at fairly fast speeds, around 500-600 fps, not bad for an energy based weapon. The plasma bolts are almost weightless and because of their shape don't encounter much air resistance, so this weapon is very accurate, and there is no bullet drop.
The weapons are designed for soldiers wearing power armor, so sights aren't necessary as the soldiers targeting systems in the HUD of their helmets provide a crosshair.