Army SF Veteran Kevin P Owens made quite a name for himself while serving in the military, but after retiring took on the position of Training Manager for FieldCraft Survival. He has created a great series of videos on a variety of topics. This is his latest.
Zeroing your rifle at 50 yards for a point blank zero of 200yards. BDC reticles are great but are only calibrated for one bullet and one density altitude