I got out of the military almost twenty years ago, and we still used iron sights on our M16A2's. Everyone had their own unique "battle sight zero" they were supposed to remember in case they had to pick up someone else's weapon.

At least with iron sights, everyone is different. I think a lot of it is just how people line up the sights, and everyone's eyeballs see different. You and I could theoretically line the sights up the same, but not hit the same POI with each others rifles.

I think scopes, however, take a lot of that away. People much smarter than myself can probably explain why.

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