We don't really "Zero" our weapons at one range, we consider it constantly fluid and changing. We have a BDC (bullet drop compensator) on our scopes for our elevation knob. We estimate the range to the target, dial in the range on the BDC along with our guessimate adjustments (for humidity, temperature, etc) and then engage (of course, wind adjustments are dialed in also). So, after you do the initial zero of the rifle at a given range, and then slip the BDC, we never really have a zero, so much as just verifying the BDC at each range when we can. I like to carry my rifle with the BDC set at 600m, and then adjust if/when needed for the target.
MEL
MEL