Myth – “Once I determine my zero from mechanical zero I can apply that dope to any rifle.”
Fact – A zero setting on one rifle applies only to that specific rifle.
FM 3-22.9, Page 5-14
“There is no relationship between the specific sight settings a soldier uses on his rifle to the sight settings he would zero another rifle to. For example, a soldier could zero his assigned rifle 10 clicks left of center, and then zero another rifle and his adjustments could be 10 clicks right of center. This is due to the manufacturing difference from one rifle to another, which makes it essential that each soldier zeros the rifle that he is assigned.”
Just as Mechanical Zero has no direct effect on actual zero, a setting from one rifle has no effect on another rifle. For example, I have had three different M16A2 rifles through the USAR shooting team. Shooting M193 ball the No Wind zero was L1, R3 and L9 from MZ for each.