1. Bullet Tumbling
Some bullet designs are less stable than others. A bullet that is stable in air may be extremely unstable inside the target—tumbling rather than simply boring straight through. This is a particular characteristic of bullets such as match-type hollowpoints in which the center of gravity has been displaced rearward. The tendency to tumble can reduce penetration and produce an unpredictable bullet path. This makes such bullets unsuited to hunting or defensive applications, but acceptable for some military or target-shooting applications.
2. Bullet Rotational Velocity
A bullet exiting a rifled barrel spins on its axis at a rate determined by the muzzle velocity and the rifling twist rate. The bullet will rotate either to the left or to the right depending on the direction of the rifling twist. The rotation stabilizes the bullet, causing it to travel point first.
The speed of bullet rotation is normally expressed in revolutions per minute (r.p.m.). Rotational speeds range from a low of 50,000 r.p.m. for a heavy, slow-moving projectile to more than 500,000 r.p.m. for a light, high-velocity bullet.
Lightweight bullets with thin jackets launched at high muzzle velocities can in fact come apart mid-air from the tremendous centrifugal force imposed by high rotation rates. However, bullet rotational speeds play only a minor part in bullet expansion once the bullet strikes the target. Some expanding bullets depend on the rotation of the sharp, exposed copper "petals" to enhance tissue destruction as they penetrate.
3. Wound Tracks
As a high-velocity bullet penetrates living tissue, it produces two kinds of deformation:
- Temporary wound cavity: The projectile's shock wave violently forces target material outward from the projectile path, creating a temporary cavity. The temporary cavity may be quite large, and its size is directly related to impact velocity.
- Permanent wound track: After a fraction of a second, the temporary cavity collapses, leaving a permanent wound track. This is the permanent deformation or destruction produced by the projectile as it plows through the target. The size of the permanent wound track is related to the bullet diameter and weight.
Because of the above, two separate schools of thought on bullet wounds have emerged. Heavy, large-caliber, low-velocity bullets that penetrate deeply are best for transferring kinetic energy to the target. This group believes the permanent wound track is the most dependable mechanism for incapacitating the target.
Low-velocity bullets, such as those from revolvers and semi-automatic pistols, do not produce a large temporary wound cavity. Instead, they depend on the permanent wound track to cause damage in the target. For this reason, large-caliber handgun bullets are a better choice than small-caliber handgun bullets for hunting and self-defense, as their larger diameter causes a bigger permanent wound track.
The other school of thought holds forth the belief that high-velocity, lightweight bullets that can create a large temporary wound cavity are the best mechanism for quick, dependable incapacitation of the target. Many exports believe that the temporary wound cavity caused by the shock wave of a high-velocity bullet creates a temporary cavity large enough to cause damage at a considerable distance from the permanent wound track. This could mean tissue damage, nerve disruption or the breaking of bones that lie near but not directly in the path of the bullet.