I developed this from an automatic weapons employment manual and did some adaptation fro airsoft. Much of it is cut and paste with comments inserted as applicable.

Weapons Employment

Both rifles and support weapons have common characteristics.

CHARATERISTICS OF FIRE

TRAJECTORY:

The trajectory is the path of the round in flight. You must know the weapon trajectory to effectively fire the weapon throughout its full range. The path of the round is almost flat at close range (In airsoft, depending on FPS, I estimate 70-90 feet) then it begins to curve, and the curve becomes greater as the range increases.

CONE OF FIRE

When several rounds are fired in a burst from any weapon, each round takes a slightly different trajectory. The pattern these rounds form on the way to the target is called a cone of fire. This pattern is caused primarily by vibration of the weapon and variations in ammunition and atmospheric conditions.

BEATEN ZONE

The beaten zone is the elliptical pattern formed by the rounds striking the ground or the target. The size and shape of the beaten zone changes when the range to the target changes or when the weapon is fired on different types of terrain. On uniformly sloping or level terrain, the beaten zone is long and narrow. As the range to the target increases, the beaten zone becomes shorter and wider. When fire is delivered on terrain sloping down and away from the machine gun, the beaten zone becomes longer. When fire is delivered on rising terrain, the beaten zone becomes shorter. The terrain has little effect on the width of the beaten zone.

DANGER SPACE

The danger space is the space between the weapon and the target where the trajectory does not rise above the average height of a standing man. This space includes the area of the beaten zone. When the weapon is fired on level or uniformly sloping terrain at a target at short to medium range, the trajectory does not rise above the average height of a standing man. When targets are engaged on level or uniformly sloping terrain at longer ranges, the trajectory rises above the average height of a standing soldier, therefore, not all the distance between the machine gun and the target is danger space. For the purposes of airsoft the danger space may well extend to the maximum range of your weapon.

Okay, how do these three characteristics come into play?

Trajectory is easy. When you know how your weapons trajectory you can compensate to increase the probability of a hit.

Cone of fire is a little more complicated. You will have to experiment with your weapon to determine its cone of fire. Once you know this, you can determine the area you cover when firing in bursts or on full automatic. You can effectively suppress any target with this cone.

Beaten zone is where I think it gets cool. Again, you will have to do some experimentation to determine your weapon’s beaten zone. As stated early this is an elliptical impact zone. The beaten zone for the AK-74 I use is approximately 2 feet wide by 10 feet long. As you can see, this can give you an advantage against multiple targets that cluster. Now combine multiple beaten zones side by side and I think you will understand.
Remember, the less accuracy a weapon has the large its cone of fire and beaten zone become. Accuracy is great but volume of fire has a quality all its own.

All of this leads to ways to take advantage of your weapon’s characteristics and maximize its effectiveness.

CLASSES OF FIRE

Weapon fire is classified with respect to the ground, the target, and the weapon.

RESPECT TO THE GROUND

Fire with respect to the GROUND includes grazing and plunging fires.

Grazing Fire: Grazing fire occurs when the center of the cone of fire does not rise more than 3 feet above the ground. When firing on level or uniformly sloping terrain, the gunner should be able obtain grazing fire out to the medium range for his weapon. Again, you need to know your weapon.

Plunging Fire: Plunging fire occurs when the danger space is confined to the beaten zone. Plunging fire also occurs when firing at long ranges, from high ground to low ground, into abruptly rising ground, or across uneven terrain, resulting in a loss of grazing fire at any point along the trajectory.

So how do you use this?

Grazing fire is handy when you have someone lay a base of fire to block an approach or pin an enemy element. Anyone trying to move through the danger space will likely become a casualty. Combine several weapons employing this technique and a large front can quickly be made in accessible.

Now plunging fire comes in handy when you want to spring a surprise. A support weapon can be placed on a reverse slope to arc rounds in, raining fire down on an enemy element trying to engage the base of fire.

RESPECT TO TARGET

Fire with respect to the TARGET includes frontal, flanking, oblique, and enfilade fires.

Frontal Fire: Frontal fire is when the long axis of the beaten zone is at a right angle to the front of the target. An example is when firing at the front of a target.

Flanking Fire: Flanking fire is firing at the side of a target.

Oblique Fire: Oblique fire is when the long axis of the beaten zone is at an angle other than a right angle to the front of the target.

Enfilade Fire: Enfilade fire is when the long axis of the beaten zone coincides or nearly coincides with the long axis of the target. This type of fire is either frontal or flanking. It is the most desirable type of fire with respect to a target, because it makes maximum use of the beaten zone. Ideally you can achieve flanking enfilade fire which maximizes your weapons effect on the target while reducing the target’s ability to return fire.

The position of the target in relation to your cone of fire and beaten zone can offset an enemy’s weapons advantage.

RESPECT TO WEAPON

Fire with respect to the weapon includes fixed, traversing, searching, and traversing and searching, and free-gun fires.

Fixed Fire: Fixed fire is fire delivered against a point target when the depth and width of the beaten zone covers the target. Fixed fire also means only one aiming point is necessary to provide coverage of the target.

Traversing Fire: Traversing fire is fire distributed in width by successive changes in direction. The gunner selects successive aiming points throughout the width of the target. These aiming points must be close enough to ensure adequate coverage.

Searching Fire: Searching fire is fire distributed in depth by successive changes in elevation. The gunner selects successive aiming points in depth. The changes made in each aiming point will depend on the range and slope of the ground.

Traversing and Searching Fire: Traversing and searching fire is fire distributed in width and depth by successive changes in direction and elevation. Combining traversing and searching provides good coverage of the target.
Free-Gun Fire: Free-gun fire is fire delivered against targets requiring rapid major changes in direction and elevation.
Use of the above techniques, against the proper targets will maximize the effects of your weapons cone of fire and beaten zone.

TYPES OF TARGETS

Targets presented to the gunner in combat are usually enemy troops in various formations, which require distribution and concentration of fire. Targets with width and depth must be thoroughly covered by fire.

Point Targets: Point targets require the use of a single aiming point. Examples of point targets are enemy soldiers, bunkers, weapons emplacements, and vehicles. Fixed fire is delivered at point targets.

Area Targets: Area targets may have considerable width and depth and may require extensive traversing and searching fire. These include targets in which the exact location of the enemy is unknown. The following are varieties of area targets likely to be engaged.
(1) Linear Targets. Linear targets have sufficient width to require successive aiming points (traversing fire). The beaten zone effectively covers the depth of the target area. Traversing fire is delivered at linear targets.
(2) Deep Targets. Deep targets require successive aiming points (searching fire). Searching fire is delivered at deep targets.
(3) Linear Targets with Depth. Linear targets with depth have sufficient width requiring successive aiming points in which the beaten zone does not cover the depth of the target area. A combined change in direction and elevation (traversing and searching) is necessary to effectively cover the target with fire. Traversing and searching fire are delivered at linear targets with depth.

TYPES OF FIRE

Distributed fire is delivered in width and depth such as at an enemy formation.
Concentrated fire is delivered at a point target such as an automatic weapon or an enemy fighting position.

take notes people, good post here very useful and informative