How do you get optimal damage out of the overheat rifile?

So I've been trying to figure out what swap hold and tap means after I saw it on a site that had damage numbers and I dont know how useful those numbers are because I dont know the method used to test the damage especially with the swap part tap is self explanatory just tap so it doesnt overheat and slow you down and hold is just hold it down until it overheats but what does swap mean I saw somebody say something about them using mgml/mgmls when swapping but I have no idea what that means or how the swapping would work for it to need those I tried looking around online but I couldn't figure it out also second question what is wrong with xenogard why do I always see it listed with a different partner skill sometimes online it says its crater enthusiast but sometimes it says its unknown intruder and im pretty confused about that one too