/ˈfī(ə)rˌpouər/
Noun The destructive capacity of guns, missiles, or a military force (used with reference to the number and size of guns available).
Firepower is a vague word. "destructive capacity" can mean a wide array of different things. In this post I'll try to highlight some of the important aspects of firepower in regards to an intended target. First though, we need to break down the qualities of a given weapon system into measurable factors such as ammunition, accuracy, rate of fire, and stability. With those qualities defined, we can start to look at how they come together to determine an 'effective range' in regards to a specific intended target. With all of that done, we can have a clearer look at firepower in regards to small arms using well defined terms.
Stability:
Stability is probably one of the easiest terms to define when it comes to firearms. A weapon system that moves less before, during, and after a shot is fired can be considered more stable than one that moves around a lot.
Ammunition:
After a bullet leaves the barrel of a firearm, the only factors that matter are the design of the bullet, how fast it is moving, where it is going, and what is in its flight path. The ballistic coefficient of a bullet is the amount of energy it looses to wind resistance during flight. Less energy absorbed by drag means a flatter trajectory and more energy delivered to the target upon impact. The consistency with which a cartridge is made can effect the velocity at which it exits the barrel and therefore effect the precision of the weapon system. Of course, more powder behind a bullet roughly translates into higher initial velocities, but this is balanced out by the weight of the bullet itself. A cartridge with a heavy bullet and a lot of powder will have a lot of muzzle energy, but won't have the velocity of a light bullet with the same amount of powder. The design of the bullet itself has an obvious effect on how it performs when it hits the target, and this is an area of much misunderstanding. All of these factors have to be considered when choosing a cartridge for a given weapon system.
Accuracy:
In regards to ballistics, accuracy is the ability of a projectile to hit its target on the first shot. It is often confused with precision, which is the consistency with which projectiles follow the same flight path. A given firearm may have a long list of attributes that contribute to or detract from its precision. The most important factor is stability. A very stable weapon will always point in the same direction when it is aimed at the same spot. This eliminates much of the error involved in launching a bullet through the air in hopes of hitting a target. Good ammunition can help precision as well by having a consistent velocity and a consistently shaped bullet. If a weapon is very precise, then it can only be considered accurate if the shooter can point it in the exact same spot every time a round is fired. Upgraded sights and other equipment can help the shooter to be more precise. In this sense, the person behind the weapon is a part of the weapon system.
Range:
Range is the distance that a bullet flies. It is another vague term that needs to be broken down to be understood. Maximum Range is the farthest possible distance that a weapon system can launch a bullet and isn't very useful when talking about firearms. Trajectory is the path of the bullet in terms of its horizontal and vertical distance from the tip of the barrel. Slower bullets have more time for gravity to pull down on them, so they have more of an arc to their trajectory. Faster bullets tend to fly 'straighter' simply because they cover the distance to the target faster and don't allow gravity as much time to pull them down to earth. Power is a part of range in that a bullet slows down as it travels through the air. If the bullet slows down too much, it may be ineffective when it does strike its target.
Rate of Fire:
Rate of fire is a count of the number of bullets that can be fired from a given weapon system during a given period of time. This can be helpful in dealing with multiple targets in a group, in quickly adjusting fire so that a target can be hit at long range, or in putting multiple rounds into a single target. Rate of fire is often balanced by a lack of stability. Very few firearms can spit out lots of bullets into a tight group.
Ammunition Capacity:
Ammunition capacity is simply the amount of cartridges a weapon system can fire without having to reload. This is primarily useful with weapons that intend to engage multiple targets or ones with high rates of fire.
Effective Range:
For my purposes, effective range is the maximum range at which a weapon system will consistently hit the target area and at which the bullet retains enough energy to dispatch the target. Whichever range is shorter is your maximum effective range.
Before an effective range can be established for a given weapon system, the target must be defined. You must decide on how much energy a bullet needs upon impact with the target so that you can determine the maximum range at which the weapon's bullet maintains that amount of energy. You must also be sure to use a bullet that will use its energy to penetrate the target.
The size of the target is another major concern. Sometimes, as in hunting game, the size of the target is smaller than the size of the creature you are shooting at. If you don't hit the target area then you don't have an ethical kill, so accuracy can determine another limit to your effective range. If you don't care about an ethical kill, then the target area can be much larger and you won't be limited to one bullet to do the job. This vastly extends the effective range of a weapon system.
Summary:
When choosing a weapon system, the chosen target and engagement scenario will determine what attributes are required to get the job done. For example, when hunting deer you would need to be able to place a bullet within a target area only a couple inches wide and retain enough energy to destroy the creature's heart and lungs upon impact. A 'good' deer rifle then would be one that reliably gets ethical shots at longer ranges. For self defense in an urban area, average engagement ranges are very short and so effective range can be sacrificed in favor of factors like rate of fire, magazine capacity, and smaller size. In a military setting, multiple targets may need to be engaged at long range so a high rate of fire and high effective range are required.
