OK guys i know for a lot of you this will be a childs play answer but i'm just stumped and being a bit of a newb to mags i've got to ask... and before i get a lot of "use the search" answers been there done that...

Anyways i've been sitting here looking at the animations on zdspb.com for the mag, both the basic 68 and for the RT and i cannot for the life of me figure out what the difference in the two is. i understand the basic premise of how they function, pull the trigger the sear pivots and cycles the on/off, higher pressure on the back of the bolt pushes the bolt forward, over coming spring pressure til it vents out the end of the bolt shooting the ball. at which point the bolts pushed backward by the spring and the sear catches the bolt, while repressurizing the back of the bolt... my question is what makes the rt... well rt i guess?