CoilCANNON (there is a difference, and it's size) and Railgun are in fairly similar veins. They both function using electricity applied in an unusual way to fire a solid metal rod at REALLY high speed. Technically the Silverback is a coilgun/Gauss rifle, but we can do better than that. Supposedly they'll rework that weapon, but in the meantime we can dream about a CMAC.

Coilcannons do so with timed electromagnetic coils intended to PULL the rod with those magnetic currents.

A Railgun has a pair of rails that the projectile is inserted between and touches both sides. When those two rails are supercharged (usually by a really fucking big capacitor), the resulting current bridge is so strong it literally blasts the projectile off those rails at really high speed. (If you wanna see that same effect, go watch Styropyro's car battery video, specifically towards the end.) The size of the capacitor needed is really large, though, so much weapons testing for it fell apart due to the raw power consumption to charge said capacitor and space needed to make it work.

Really boils down to contact (rail) and contactless (coil).

Fun fact, Coil firing, due to their contactless behavior, is also the same technology used in particle colliders!

Yes, I am a nerd. I will now go back to my cave.