A marksman is a person who is skilled in precision shooting.[1][2] 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.
The proficiency in precision shooting is known as a shooter's marksmanship, which can be used to describe both gunnery and archery.
a. A person skilled or practised in shooting.
a person who is skilled in shooting at a mark; a person who shoots well.