The Collaborative International Dictionary of English v.0.48:

Rifleman \Ri"fle*man\, n.; pl. Rifleman. (Mil.)
   A soldier armed with a rifle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rifleman
    n 1: someone skilled in the use of a rifle
    2: a soldier whose weapon is a rifle

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "rifleman":
   Amazon, Nimrod, Zouave, air serviceman, archer, artilleryman,
   bersagliere, bowman, brave, cannon fodder, cannoneer, carabineer,
   chasseur, crack shot, dead shot, deadeye, dogface, doughfoot,
   expert rifleman, fighting man, food for powder, foot soldier,
   footslogger, fusileer, good shot, grenadier, grunt, gun, gunman,
   gunner, halberdier, hoplite, hunter, infantryman, legionary,
   light infantryman, man-at-arms, marksman, markswoman, military man,
   musketeer, navy man, paddlefoot, pikeman, rifle, serviceman,
   sharpshooter, shooter, shot, sniper, soldier, spearman,
   targetshooter, toxophilite, trapshooter, warrior, warrioress