The main difference between Sharpshooter and Marksman is that the Sharpshooter is a soldier who is highly proficient with firearms at a distance and Marksman is a person who is skilled in precision shooting
A sharpshooter is one who is highly proficient at firing firearms or other projectile weapons accurately. Military units composed of sharpshooters were important factors in 19th-century combat. Along with “marksman” and “expert”, “sharpshooter” is one of the three marksmanship badges awarded by the U.S. Army.
A marksman is a person who is skilled in precision shooting using projectile weapons (in modern days most commonly 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.
A person trained to shoot precisely with a rifle; a marksman.
A man or person skilled at hitting targets, as with a firearm, bow, or thrown object.