Someone that is good at using weapons is called a marksman or markswoman or weapons expert.
A marksman or markswoman is a someone who is skilled in precision shooting.
In modern military usage this typically refers to the use of projectile weapons such as an accurized scoped long gun such as designated marksman rifle (or a sniper rifle) to shoot at high-value targets at longer-than-usual ranges.
Marksmanship refers to a person's ability to fire a weapon both accurately and consistently at a target.
Having good marksmanship means that a firearm user can hit their target from a distance with the fewest rounds fired.
Sharpshooter – A shooter must achieve 31 – 42 destroys and pass at least 2 iterations of any two drill types.
Marksman – A shooter must achieve 15 – 30 destroys as well as pass at least 1 iteration of any drill type.
The skill snipers are most known for is their marksmanship.
The ability to hit targets as far as a 1,000 yards away (10 football fields!) is not something that comes naturally.
Snipers train to become expert marksman with a deeply ingrained understanding of the principles of ballistics.