Lots of threads on ar15 about the topic. I guess the 2-3:00 is subject to opinion like 3-4:00 is but haven’t found any other charts but this one:
Also, HK416/MR556 buffet weight is 5.4oz, same as a H3. I run a 4.6oz buffer with a flat wire recoil spring with AGB with good ejection using mostly wolf gold ammo.
Also found this chart as well: