I strongly believe that the gauss rifle should have 'slug' ammo rather than a built-in slug factory. I wondered but then realized, having to load slug mags after 5 shots and then load a MC separately as the power source would be messy. On the right side of the weapon you can see the actual 'slug' magazine of the weapon. How the discharged MC is ejected is not shown.
Animation shows you loading ONE MC in to the power core chamber. YCS/186 the unique gauss rifle (many people on steam think of it as a beam weapon as V.A.T.S cinematic doesn't show the slug/bullet hitting the target) uses 4 MC. So this is my 3rd New Vegas playthrough (balanced) and thought I shoud say something about how I felt about something that I liked very much in the game but in the end I hated so much. That game sucked me in and made me sit on glue. Played Fallout 3 over 750 houres with all DLC. Been playing Fallout 1 and 2 in the past years.