Aim low. The weapons in this game are shown from holding it with both hands at waist length and not over the shoulder. Weapons like the AK that kick up when you shoot will have an automatic headshot when you aim low. It's always been like this since 1.5 and it hasn't changed. What has changed is the ability to get easy HS in source because of the hitbox around the head as oppose to 1.5 1.6. Aim low.