I use as heavy a buffer as the gun will lock the bolt back on an empty mag. It surprised me that my mid length Noveske actually needed an H2 to run properly.
A Daniel Defense carbine gassed I had needed only an H buffer.
It must lock the bolt back on an empty mag and eject spent cases at 4:00 It all depends on the port size. But you'll really feel the difference when shooting off hand.
