It's, like, 0730 and I've been up all night detailing guns. My stomach feels like shit and the Coca Cola is not helping. Enjoy. Please.

It's a coilgun, not a railgun. The difference being that the projectile from this one makes no contact with the barrel, while a railgun sends a bullet cascading down a pair of third rails you find on the subway.
This one uses magnetic neodymium pellets while a railgun uses, um, well the same thing, but with wheels on it.

The special "armor" Roxy's wearing helps her pick up the gun so she's not like Bastion from Overwatch. Leg bracers and a tripedal extent help her stand still when she is like Bastion from Overwatch.
The barrel does not rotate and the holes on the front provide a laser crosshair.
The 6 sets of larger coils at the bases of each barrel aid the bullets in getting extra initial speed by generating a more powerful field, and the capacitors add a slight delay between each coil so they don't all fire at once.

Oh my god, I ramble when I'm tired. Let's just hope I don't fall into a bowling lane.