Cover is by far the better way to avoid getting shot because you get to add a cover bonus to your defense roll. Cover is rated from 10% to 90% based on how well it allows you to cover yourself while shooting. A flat sturdy object tall enough to full conceal a crouching person gives 50% cover, a narrow window you can just peer out of is 80 or 90%, a telephone pole is 10 or 20%. Each 10% cover gives a +2 cover bonus. Thus, for evenly matched combatants, the delta will usually come out in favor of the defender. This means they have managed to avoid getting shot, however, the closer the shot comes the more frantic effort they have to spend ducking in and out of cover to avoid being hit while still returning fire. The defender spends 10 - delta effort. If the attacker wins, they have managed to score at least a graze, attacker's delta usually represents a better hit, and is spend increasing damage at a rate determined by the weapon fired.
Defender wins: Spend 15-delta
Attacker wins: graze + delta*(gun delta damage)
Dodging is much harder, when a defender is dodging and does not have cover within a few meters to dive to, they must spend more effort, 20-delta.
If a character is hit with a bullet, they loose body equal to the damage of the attack, or half that ammount if the shot hits a limb. They also likely take a wound.
Guns have a damage and a penetration. Damage reflects how big of a hole it tends to punch in people and thus how serious of a wound it causes. Penetration is how good the gun is at punching through armor or cover. The kind of ammuniton used with a gun frequently affects its damage and penetration values.
Armor: Armor specifies what locations it covers and has a resistance value. If a bullet hits an area covered by the armor and has penetration lower than the armor's resistance, the armor has holds and the bullet has reduced effectiveness depending whether the armor is hard or soft.
Soft armor (kevlar bulletproof vest or) designed to stop bullets from skewering the wearer by spreading the force out over a large area. A shot which does not penetrate soft armor does half its damage as water damage, and has a much lower chance of causing injuries.
Hard armor (alloy or ceramic plates) is designed to stop or deflect bullets. It is much heaver and more encombering than soft armor for a given resistance, but shots that do not penetrate do only 1/10 of their damage as water. If a shot penetrates hard armor with a pierce delta of less than 5, it deals only half damage, if 5 or more, then it deals full damage.
An attacker can choose to aim for weak points in armor when they declare their attack, in that case half their delta is spent increasing penetration and half on damage. 1 point of delta buys one point of penetration penetrating cover: Cover also has a resistance. If a weapon has penetration higher than the cover's resistance the cover's bonus is halved. However, if the penetration is less than 5 higher, damage is halved unless the attack's delta is at least half the cover bonus (shot hits them through the cover but is slowed)
For list of possible attacks see attacks in tick-based combat
Instead of rounds, combat is based on more-continuous time "ticks", that represent about half a second time. Not every player is expected to act every tick.
GM announces ticks every few seconds or so, and each player may announce an action during a tick. If two or more characters act in the same tick, both actions occur simultaneously (note: this gets rid of initiative. We need to be sure nothing else breaks. Also, this is OK for melee strikes/bows/whatnot, but do we want to still have some sort of initiative for firearms?). Once a character announces an action, others can continue to announce actions for the same tick, before opposing rolls are made (or some variations on this. Ideally, actions should be announced quickly, as any reaction beyond a basic one (e.g. beyond "I strike him before he moves back" or "As he moves, I follow him") should probably be on the next tick, but I don't know how and if we want this in the rules). Reaction to opposing rolls (i.e. whether a punch hit or not), should definitely occur on the next tick, but it's to be determined how to handle the initial roll in that regard.
Hand to hand attacks have stability cost, representing the time you need to recover from the attack (thus attacks are not likely to happen every tick). Stability cost will be discussed in more details later.
Most melee attacks, such as punches, involve preparation and the attack itself. First the attacker makes his roll, (representing preparation — in case of a jab it represent looking for an opening and getting in position to jab, in case of a stronger attack it also includes some initial motion), and after the roll can decide to abort the attack. Aborted attack only costs half effort and stability, but has no chance of doing damage. The reason behind attacker-first rolls, is that rolls can be done much quicker that way, and ideally decision on aborting the attack should be made within seconds (perhaps 1-2 seconds once players get used to the system).
Moving 1 square takes a full tick. If running, the character moves at around 2 squares per tick on ticks after the first, but can not take most offensive actions, or they are at a large penalty.
Guns may or may not impose stability penalties (if you are shooting a big gun and/or are not that strong you will get them, shooting a 9mm pistol in two hands will not unless you are a real wimp), instead they mainly use an aiming mechanic. Actually firing a gun happens in a single tick, but represents a reaction shot, snapping your gun to take a shot, and carries significant penalties for range (you can pull up your gun and hit someone if they are standing right in front of you, it will be much harder if they are a distance away. Spending a few ticks aiming at a target will allow you to reduce the range penalty and the tick penalty recovery table. Any shot you spend more than 4 ticks aiming uses aimed shooting instead of point shooting.
This table shows how your tick penalty recovers. You look at the line for your current penalty, cross reference with how many ticks have elapsed, and look up what your new penalty will be. You can just update every tick and shift to a new line on the table, it will give the same result, but the extra columns are provided for convenience when multiple ticks pass without your acting or interacting.
(for mathematically inclined, the recovery is square root of stability penalty, rounded down. But do print out a table, attempting to calculate several ticks worth of updates is too time-consuming otherwise).
Guns impose stability penalties. Penalty for bringing a gun up to ready is Pistols: 10 Rifles: 20 Carbines: 13 Assault Rifles: 17
Range Penalties are Pistols: +5 point blank, -1/2m Carbines: +4 point blank -1/2m Assault Rifles: + 3 point blank -1/3m Rifles: +1 point blank -1/4m
You can continue aiming adding aim bonus up to 1/2 the range penalty (round up) at a rate of 1 point of bonus per tick aiming.
If you fired upon while aiming, it spoils your aim. For every point of effort you spend avoiding being hit, you get 1 stability penalty.
Each shot imposes a 3 stability penalty. Firing at all in a round imposes an extra -7 stability penalty after all shots in the round are fired. Some big guns have larger penalties, some, particularly assault rifles have the ability to let you fire the first three shots before the stability penalty comes to bear. You may roll your attack roll, decide it is a poor result and take the -7 stability penalty but not fire (avoiding the extra -3 and not wasting a bullet), this represents you coming out to fire then realizing it they are currently keeping their head down and deciding not to pull the trigger.