Basic Ballistics
The deadliness of a bullet is determined by its mass, its speed at impact, and the rate at which the bullet slows after impact (accuracy, of course also matters, but that is more a factor of training than of the weapon. Most modern rifles are capable of more accuracy than the person shooting them.) Here I will be discussing the first two factors, mostly ignoring the way some bullets are designed to slow more quickly (e.g., hollow point bullets). Combining velocity, mass and distance, it is possible to calculate the impact energy of any projectile, including bullets. All other things being equal, the greater the impact energy, the more deadly the bullet.
When designing a bullet, engineers must consider the size, shape and explosive charge that propels a bullet (larger charge=faster bullet). Whatever the design, the moment the bullet leaves the gun, it slows down. The impact energy of a bullet at 50 yards will be greater than the impact energy at 200 yards. The standard distance for evaluating the impact energy of a rifle is 100 yards.
Based on this simple understanding of ballistics, people might guess that the deadliness of ‘assault weapons’ is because they have higher impact energies than hunting rifles—but critically, that is not true. In reality, the impact energies of ‘assault weapons’ are typically less, often far less, than a typical hunting rifle. Here I will use the impact energies calculated by Hornady, an ammunition maker who publishes detailed ballistic information for all of their extensive line of bullets.
Using Hornady’s Standard Ballistics Chart, the typical ammo for an AR-15 (e.g., .223 Remington or 5.56 NATO) the impact energies range between about 900 and 1200 ft/lbs at 100 yards. In contrast, a .308 Winchester round (a standard all-purpose hunting round) has impact energies ranging from about 2500 to 2800 ft/lbs at 100 yards—more than twice the impact energy of a round fired by a typical AR-15. More so, since the ammo used in an AR-15 is smaller than a .308 Winchester round, the impact energies at distances greater than 100 yards drop off much more quickly for the ammo used in an AR-15. So, strictly looking at the impact energies of a single bullet fired from an AR-15 and a ‘standard’ hunting rifle, the hunting rifle is far more deadly—at all distances.
So, given this, shouldn’t we be banning hunting weapons rather than ‘assault weapons?’ No. Up to this point, we have been talking only about a single bullet, which makes sense when talking about hunting. Hunters try to take their prey with a single shot for ethical and practical reasons. Most hunters do not want to cause undue suffering to an animal and they do not want the animal to run, forcing the hunter to track the animal to where it died. In dense woods, tracking can be a nightmare…often resulting in losing the animal. For both practical and ethical reason, hunters want to kill their prey--with a single shot--as close to instantly as possible. Hunters are also typically shooting at medium to long distances. Most critters are very good at sensing hunters and bolting before they get close. Hunters need a rifle that has high impact energies even at distances greater than 100 yards. Finally, hunters rarely have time to shoot more than two times at the same animal. They either kill it or it runs away well before they have a chance to take more shots. Given all of this, an AR-15 is an awful hunting rifle and a rifle based on .308 Winchester ammo is pretty good.
In contrast, the design of assault style rifles is intended for another purpose—close to medium range combat. The ammo fired from an assault weapon is typically smaller, but with higher muzzle velocities, creating a weapon with its ‘peak’ effectiveness at the short to medium range. With a single bullet, an ‘assault weapon’ is actually more likely to wound a person than a hunting rifle. This is not an accident. The idea is that by wounding an enemy in combat, several enemies will be forced to help that person and stop returning fire. To make up for its lower impact energies, ‘assault weapons’ are designed to shoot more bullets in a shorter period of time. To phrase it simply, if a hunting rifle can deliver one bullet with about 2,700 ft/lbs of impact energy, an AR-15 can deliver multiple bullets with about 1,000 ft/lbs of energy. More so, since people are less quick (and less tough) than most deer, the first bullet slows people enough so that they can be shot again. For this reason, ‘assault weapons’ typically carry more ammunition and can fire it faster than a hunting rifle. To phrase it simply, ‘assault weapons’ are favored by those who want to shoot up movie theatres, grade schools and shopping malls because these weapons are designed for exactly this sort of short to medium distance shooting.
Taking all this into consideration, A rifle that shoots (1) many, (2) large bullets with (3) high muzzle velocities would be more dangerous than a rifle that can shoot (1) few, (2) small bullets with (3) low muzzle velocities. The best way to evaluate the deadliness of a rifle is to develop a formula that combines the impact energies at 100 yards with the rate of fire per minute—what I will call the Cumulative Impact Energy per Minute (CIEpM). Critically, this formula does not address how many bullets fit in a single magazine, nor does it address how quickly a magazine can be changed—only the number of shots an average user can shoot in a minute. It could be one large magazine that is a pain in the ass to switch out, or a small magazine that is really easy. The only question, in terms of its danger is how many shots per minute, however achieved.
Using the CIEpM formula (impact energy x rate of fire per minute), it is easy to see the difference between an assault weapon style rifle, and a hunting rifle. Depending on the magazine size, an assault rifle can shoot many, many bullets per minute, though sustained fire tends to make them jam. In contrast, a bolt action rifle requires manually pushing bullet into the firing chamber, slowing down the rate of fire. Many hunting rifles have magazines with 6 bullets, and magazines that are slow to change. ‘Assault weapons’ in contrast can have magazines with 20-30 bullets, and easily switched magazines. Thus, using .308 ammo in a bolt-action rifle with a 6 shot magazine, the rate of fire per minute is about 6 shots—with a CIEpM of 2700 x 6 = 16,200. In contrast, a semi-automatic assault style rifle using .223 Remington ammunition may be able to shoot 30 or more bullets in one minute (not sustained)—with a CIEpM of 1000 x 30 = 30,000. Thus, a semi-automatic assault style rifle, like an AR-15, does roughly double the damage as a ‘typical’ hunting rifle when viewed in terms of CIEpM.
A Better Assault Weapons Ban
So, in order to make the new assault weapons ban better than the poorly conceived 1994 Assault Weapons Ban, we need to abandon the definition based on presence of bayonet mounts, flash suppressors, and grip type and replace it with a definition based a rifle's Cumulative Impact Energy per Minute at 100 yards. First, by calculating a ‘typical’ hunting rifles CIEpM, we can establish an upper limit necessary for hunting. Using the most powerful .308 Winchester ammo available and 8 shots a minute as ‘typical’, the CIEpM of a ‘typical’ hunting rifle would be about 22,400 (2800 ft/lb x 8 shot per minute). Just to add buffer, lets say that a maximum CIEpM of 25,000 is more than sufficient for any hunting rifle. That is, any rifle with a maximum CIEpM over 25,000 could be banned without causing undue difficulty for hunters.
In practice, establishing 25,000 as a maximum CIEpM would have several benefits. First, it would allow gun makers significant flexibility in terms of making hunting weapons. For very large game, rifles could be designed to only allow 5 shot per minute, but impact energies at 100 yards of 5,000 ft/lbs. Smaller calibers, suitable for target shooting, could have higher rates of fire. Rifles could even keep the ‘assault style’, but could not fire more than 25 shots per minute (assuming 1000 ft/lbs at 100 yards).
The second benefit of using CIEpM to define banned weapons is that it would prevent gun manufacturers from skirting the law. Calculating the impact energies is well established, and the rate of fire could be easily determined by having multiple average shooters use a new weapon for a few days and average their rate of fire. If the CIEpM is too high, that gun is not legal for sale to the general public. More so, a similar formula could be used to determine which handguns should, or should not be legal (I have not yet worked out this out, but provisionally I think the maximum CIEpM of handguns should be about 6,000 at 50 yards—based on 12 shots per minute from a .357 revolver)
I suspect that there could, and should, be debate over the specific maximum CIEpM value for rifles. As I see it, 25,000 is actually fairly high maximum CIEpM. Really, it would take no more than a rifle with a maximum CIEpM of about 10,000 to take down all but the largest game (4 bullets at 2,500 ft/lbs, 3 bullets at 3,300 ft/lb or 2 at 5,000 ft/lbs).
In the end, however, the most important element of using CIEpM to determine whether a rifle is banned or not is that it would end the practice of using rifle bling (e.g., things that make a rifle look bad-ass, but actually aren’t dangerous) as the defining characteristics of ‘assault weapons.’ This was a central problem in the 1994 Assault Weapons Ban, and continues to be a problem in the revised assault weapons ban currently on the table. Using the CIEpM to determine whether a rifle is, or is not, legal would use the characteristics that actually make a gun dangerous to determine whether a gun was too dangerous to be available to the general population. That, at least, would be a step forward.
