The following article is not about gun control, per se, as a means of stopping school shootings. When nothing changed after the shooting of first graders at Sandy Hook most of us despaired of anything meaningful ever happening because of the hold that the arms industry has on Congress.
This is about Florida laws that restrict the sale of pistols to those over 21 while allowing an 18 year old to buy an AR-15 style semi-automatic rifle. Note that the ammunition fired by the M-16 uses a 5.56 caliber round, that caliber is nearly identical to the .223 Remington round used by the AR-15; one is in millimeters and the other is hundredths of an inch. The .45 round used in pistols is nearly half an inch in diameter.
Today, it came out that the school shooter in Parkland, Florida bought the AR-15 style rifle used in the shooting when he was eighteen years old. In Florida a pistol (“handgun”) cannot be purchased by anyone under twenty-one. The thought behind this law or laws is not clear.
The damage that can be done by either weapon is considerably different. The reason lies in the physics behind what is termed ‘force’ in physics: F=1/2 MV^2. Note that the force on impact of a bullet varies directly to “M” the mass, while it increases with the square of the velocity, "V". If we compare a .45 caliber round coming from a semi-automatic pistol to the .223 caliber projectile coming from an AR-15 the mass of the .45 is about 250 grams and the .223 is typically 55 grams. It might seem that the .223 would be much less harmful, but the velocity of the .45 is about 800 fps whereas the velocity of the .223 is about 3,750 fps. The force of the .223 traveling through tissues spreads to the side creating what has been termed hydrostatic shock. A pistol round basically creates damage to the structures it passes through relative to the size of the bullet, whereas a high velocity round creates a crush effect to tissues surrounding the path of the bullet. In addition, the 5.56 caliber or .223 rounds yaw, break apart, and create a large terminal cavity.
What these facts don’t immediately tell is that the tissues adjacent to the track of a high velocity round, even though they come back to fill in the temporary cavity are dead for some distance around the track.
In Vietnam we debrided wounds around the track to the point that the tissue bled indicating intact blood supply. That distance could be several centimeters to the side of the track.
The following video asks whether three rounds to the chest by an AR-15 could be survivable.
The following slow motion video demonstrates the damage to a gelatin block.
The point of this discussion is that, any other considerations aside, the laws surrounding age limits on buying firearms in Florida are poorly thought out. If the ability to conceal a weapon is the only consideration it is faulty. The Parkland shooter concealed a rifle on entering the high school, and the shooter in Las Vegas, Nevada concealed an arsenal being taken to his room.
If the argument is that a pistol is only meant for shooting people while the AR-15 could be a hunting rifle, that is a poor argument. The AR-15 would make a lousy hunting rifle because the round creates a lot of tissue damage, and because no one needs a semi-automatic rifle for hunting. The .223 Remington is sometimes used for shooting prairie dog sized “varmints” and is usually fired from a single shot or bolt action rifle.