Originally Posted by
BoilerUp
Isn't the 308 buffer the short stubby one? If so, that should only be used in the AR15 carbine length buffer tubes as those are too short for the AR10/A5 extensions. I made the mistake once of running a 308 buffer in a AR10 extension and ended up damaging the threads on the rear of the lower receiver from bcg over travel.
That said, in principle I think you are right as the .308 buffer is about the same weight as an H buffer, so I'd probably start with an H instead of the H3.