So. Getting hit is deadly. How do we hit then? The answer is by odds.
X-com Ufo Defence has a percentage-based shooting system. Depending on the weapon used there are three choices: Autofire, which uses half of your action points to shoot 3 inaccurate shots, Snapshot, which is more accurate and takes one third of your action points, and Accurate Shot, which takes the whole turn but is extremely accurate (depending on the distance and accuracy of the unit). Let’s take this system and modify it a bit.
While we do not use turns per se, some characters still might be faster than others and therefore act faster. Every character has a property, either Reactions or Initiative. The first action of each character is ordered by Speed. So if two characters shoot at each other with Snapshot-attacks, the character with higher speed takes the first shot. The first attack is important, because the enemy has not yet reacted to it; If the Suppression check succeeds, the enemy darts for cover, spoiling the other shots that could come. Characters with the same speed act simultaneously.
There are three possible types of attack: Suppressive Fire, Snapshots and Sniping. Suppressive Fire is inaccurate, with a large target circle (more on that later). It takes a lot of ammo, but has a high Suppression rating. The amount of shots fired depends on the weapon itself. A failed Reactionary attack (A failed Nerve check) is always Suppressive fire, since surprised units rarely aim.
Snapshots are where the roleplaying comes in. A snapshot is a compromise between speed and accuracy; A quickly-aimed attack whose function is to hit a target out of cover. The attack is made in initiative order. A successful Reactionary attack is always a snapshot. The accuracy of the attack depends on cover, distance and the accuracy of the attacker, meaning that a snapshot can be improved with experience. Snapshots have a relatively low suppression rating, since the shots aren’t very numerous or accurate.
Sniping is an attack for killing enemies behind cover. A snipe shot functions a bit differently; The attacker begins aiming at his target at his Initiative count. Every time unit, (perhaps seconds) the accuracy rating grows higher. Since the point of the attack is to hit the enemy, the attacker will not make the attack before the accuracy has grown to a certain point and the enemy is within sight. Since aiming requires a long time, there are ample opportunities to interrupt a sniper. Therefore sniping usually happens from a hidden position, or while another person is suppressing either the target or anyone who could interfere. Sniping has an extremely high Suppression rating due to the proximity of the shot to the target, but since it is taken very late, it usually does not prevent the enemy from doing what it wants.
Each individual shot is calculated with raycasting; The computer casts a ray with random deviation at the target. The amount of deviation depends on the accuracy of the attacker and the attack type. Then it just sends a bullet along that vector and calculates whether the it hits anything of interest. Since the shots cannot be calculated in advance, the UI will not give the player exact odds of hitting. This way the game depends less on probability management and more on tactics.
So. This is how fighting with ranged weapons from behind cover works. Fast combatants usually are given either sniping or suppression job, since both actions depend on working before the enemy does. When the enemy is in the open, snapshots are a fast and certain way to drop them.