Well, I did a bit of houseruling for firearms for "All Fall Down" last summer.
It went a bit like this:
Wild Fire: Wild fire can be performed by anyone. This is essentially spraying the area down without regards to anyone actually being hit. Wild Fire covers a 10x10 area, and expends the entire magazine of the weapon or fifty rounds, whichever is less. There must be a minimum of six rounds within the magazine for this to work. Anyone within the 10x10 area must make a Reflex Save (DC: Attackers attack total) or be struck by a single round. If there are more people in the area than rounds in the weapon, they are considered to have been grazed, hit by bullet fragments, or hit by a through and through ricochet. Firing Wild Fire has a -4 attack penalty.
Aimed Shot: An aimed shot is your typical
Burst Fire: Burst fire entials either a quick squeeze of the trigger to expend a small number of rounds via automatic fire, several quick trigger pulls on an automatic weapon, or a weapon with burst fire mode. The weapon requires at least 3 rounds remaining. The burst is -4 to hit (unless Burst Fire feat is possessed, in which case it is only -2) and does an additional die of damage. Burst fire can be used to hit two adjecant targets that have not more than 1 foot between them.
Aimed Burst: This is dropping the entire burst into a single target, usually center mass. The penalty for this is -2 (nothing if the Burst Fire feat is possessed) and the target is considered to have been hit by all three to five rounds (depending upon the weapon). This can only be done untrained if the weapon has burst fire mode. The feat Burst Fire allows someone to do a short burst of automatic fire that expends between 3 and six rounds (1d4+2 rounds) and the target is considered to have been hit by ALL the rounds if the attack roll is successful. The target is granted a single reflex save (DC Attackers total attack roll) for half damage.
Directed Automatic Fire: This is hosing a single area, usually 2 5' area, with directed fully automatic fire, using fire saturation to overcome cover and concealment. A minimum of 10 rounds must be used, and it expends 25% of remaining ammo (or 10 rounds, whichever is greater). If the attacker makes an attack roll for each 5' area. For every 2 points above the target's Defense, the defender is hit with an additional round. Advanced Firearms is needed for this action and the attacker suffers a -2 penalty.
Autofire: This is commonly known as "Spray and Pray" where a large volume of ammuntion is put out in order to hopefully hit as many people as possible. One quarter of the ammunition is expended (or 10 rounds, whichever is greater) when this is done. Autofire covers a total of 10 5' blocks, with the round divided evenly. Targets within the area gain a single reflex check in addition to normal Defense to avoid damage (DC: Attackers total attack). Attackers who fail thier check are hit by the amount of bullets within the 5' area. Without advanced firearms, the amount of bullets is halved (the rest are considered lost due to recoil) and the attack is made at -8. With Advanced Firearms, and autofire attack is made at -4.
There's a bastardized version of the rules, since I'm not adding in the recoil and recoil compensation effects.