Silly question, but... RIFLE buffer, right? You switch from a carbine system to rifle system, complete?
308AR rifle buffers are 5.200" long, for DPMS and Armalite=based recoil systems, so it doesn't matter which one you grabbed, honestly. You also went from about a 3oz buffer to a 5 1/2 oz buffer. That should have slowed down your recoil impulse.
I don't care about those clock-charts, that show which direction brass is ejecting, and all the voodoo it means. I care THAT brass is ejecting, and my rifle functions.