I never liked the "Spray weapons use a number of rounds equal to the dice in your pool" rule. It makes a more skillful shooter use more ammo. I also generally think Spray ratings make automatic weapons far more overpowered than I would like. I'm not arguing that they are or aren't in real life, but I feel the ability to use all sets for free is a powerful bonus on its own mechanically. 

1. Each die of Spray used equates to about 10 rounds fired. You don't have to use the entire Spray rating with your attack. If your weapon's one of those little buzzsaws, like a MAC-11 or Micro-Uzi, just assume that using your full 4-5d Spray rating empties the magazine.

2. 2/3-round bursts add +1d to your pool, allow you to use up to 2/3 sets, but can only be used on a single target. NOTE: Not sure about the +1d to your pool thing, I may drop it for my game but allow a 3-round burst to benefit from aiming.

3. For semiautomatic weapons, the number of rounds actually fired is equal to the lowest loose die in the your pool or the number of attacks made, whichever is higher. If there are no loose dice, use the Height of the shortest set. This makes a skilled shooter more likely to do the job with single shots, while a less experienced gunman is more likely to spray and pray.

Aimed shots only use one round.

A generation later, the children of the late Danger Cho and Tiger Jones are at it again, each thinking the other's father killed their own. Danger Jr. has a Pistol pool of 8d, but Lil' Tiger has been at school, not the range. His Pistol pool is only 5d. Danger gets a 1, 2, 4, 3x8, 9, 0 - a fine shot to Lil' Tiger's chest that only uses one round (the lowest loose die was 1). Tiger rolls 4, 5, 2x7, 8. Not only is his 2x7 ruined by Danger's faster set, Tiger also wastes 4 rounds hitting nothing but air.