M2HB (both turret and pintle mounts) have issues where the first 1-2 shots are on target (when tap firing), the remaining shots in a burst will be low and to the right of the iron sights.
To reproduce.
Load into any game mode, preferably game master
Spawn M2HB
Tap fire and observe bullets hitting a wall (usually a little high at closer range)
Go full cyclic for 2-3 seconds and observe shots landing down and right of where the sight is pointed at initially
Use of diag commands such as projectile trace, infinite ammo, FoV override, disable wind.
Observed as well in stable patch 1.6.0.119.
Not observed Russian counterpart NSV.
Linked are three different videos, two are showcasing the tripod/pintle version on a custom map, one in the diag version of the current experimental build.
(uploading files wasn't working)
https://youtu.be/p6TrDVJBB9s
https://youtu.be/5xHQQERhzR0
https://youtu.be/k-ejla-nmGk