lots of variations to work with.
If you are shooting a gun all day, I also take you are at least putting 100 rounds downrange. In 100 rounds I would hardly believe they will all fit into under moa.
There are so many things that can go wrong.
No one can make perfect shots all day long in hundreds of rounds without at least contributing some level of shooter error himself.
No one can dope the wind precisely all day long either under variable wind conditions.