)Wouldn’t go with Armalite unless your buying a complete rifle. As far as keeping the same buffer and spring, it depends on a huge amount of variables. I suggest reading the Primer puncture thread under General discussions. It covers a lot more then that but gives you an idea of everything involved when switching from 308 to 6.5 Cr. Different pressures and pressure curve, gas velocity, and a whole lot more. Pretty confident you would need to do some experimenting for the right buffer/spring for 6.5 or you might get lucky and they would swap out ok.