Riflemen are skirmishers and snipers without peer, picking off leaders to sow confusion in enemy ranks.
Whether they are called light infantry, jaegers, tirailleurs or chasseurs à pied, it is the job of these men to screen the main battle line, harass the enemy and, if possible, pick off important men in the enemy’s ranks. Unlike their fellows in the line infantry, light infantrymen are trained to think for themselves, use the ground and cover intelligently, and not fight in rigid lines. Instead, they form a loose skirmish line and fire independently at their own designated targets. The effect is a constant, low-level barrage rather than the crashing thunder of a volley but the effect is quite deadly as officers and sergeants are picked off and removed from the fight. Against cavalry, however, their best defence is to withdraw to their own battle line.
Historically, the Austrians were widely regarded as producing the finest light infantry forces in Europe. Other nations did catch up, but in the case of Britain and France it was their experiences in fighting in North America that persuaded them of the wisdom of light troops. Battle lines were simply impossible to manage in the dense woodlands, and largely pointless against the native tribes!
Riflemen are long-ranged skirmishers, outclassing regular light infantry in terms of the distance they can shoot by a considerable margin. However, they pay for this advantage with considerably slower reload times, as rifles take longer to reload than muskets.
Riflemen, and their equivalents, have much of the same qualities as light infantry: both can use Light Infantry Behavior, both have all of its men fire simultaneously, both can deploy stakes etc. Their large range bonus, combined with their light infantry behavior, also mean that they are very suitable for (relatively) safely engaging enemy artillery. However as with most skirmishers they are vulnerable to melee and so, should avoid melee situations.