Much speculation exists as to the causes and effects of the wounding mechanisms of small arms ammunition. When a small arms cartridge is fired, a large portion of the energy from the propellant is spent doing things other than propelling the bullet towards the target. Engraving the bullet into rifling requires significant energy but is necessary in order to spin-stabilize bullets that do not have fins or some other method of gyroscopic stabilization. We utilized a Walther P38 semi-automatic 9x19mm Luger handgun (Figure 1) and a Dan Wesson 45ACP M1911-style handgun (Figure 2) to shoot (6) different brands of Jacketed Hollowpoint (JHP) ammunition into standard 20% ballistic gelatin blocks. The bullet impacts were recorded on slow motion video at 42,000 frames per second with a Photron Ultima SA5-775K Monochrome high speed video camera (Figure 3).

All shots were fired from 10 feet distance, measured muzzle to the impact face of the ballistic gelatin blocks. Tested ammunition for both 9x19mm and 45ACP included: Cor-Bon DPX, Federal Expanding Full Metal Jacket, Federal Hydra-Shok, Hornady XTP, Remington Golden Saber and Speer Gold Dot. Utilizing the Conservation of Energy law, it is reasonable to assume that the difference between the bullets rotational energy immediately prior to impacting the gelatin block and the rotational kinetic energy measured at the last three inches of bullet penetration in gelatin is equal to the kinetic energy dissipated radially into the ballistic gelatin block.

The rotational velocity of a bullet is a function of the twist rate of the barrel and the muzzle velocity. Similarly, the rotational kinetic energy of a bullet is a function of the mass, diameter and rotational velocity.

E_rotational=½Iω²

where I is the moment of inertia and ω is the rotational velocity. For the purpose of this report and determining the moment of inertia, the JHP shape has been generalized to be a “solid cylinder”.

In the shot depicted in Figure 4, the bullet was rotating at 5586 revolutions per minute at impact and was rotating at 2550 revolutions per minute at the end of the ballistic gelatin block. This corresponds to an initial rotational kinetic energy of 48 ft-lbf and a final rotational kinetic energy of 21 ft-lbf. It is then reasonable to assume that this bullet did 27 ft-lbf of damage to the gelatin between 0 and 8.5 inches penetration. All shot data presented in Tables 1 and 2 was analyzed in this manner.

We see that the fraction of kinetic energy lost in rotating the gelatin is the same (5% of impact KE) for both tested calibers and impact velocity range. For reference, this is two to three times the kinetic energy at the muzzle of an adult airgun. Differences in result between bullets can be explained by the shape of the expanded bullet and the degree of stability of each bullet as it penetrates the gelatin. In short, a less stable bullet will be likely to retain less rotational velocity due to increased fluid pressure acting on the front or ‘wetted’ area of the bullet. Similarly, the trend of this study points towards expanded JHPs having an appearance more like a propeller as transferring more rotational energy to the target than a JHP having a disk shape.

The weapons chosen for this test were chosen because the twist rate and length of the barrel are typical for 9x19mm and 45ACP handguns. It would be interesting to see further research into the effects on handguns lethality by a change of barrel twist rate. On the one hand, increasing the rotational speed of the bullet aggravates the wounding done by the tissue being displaced radially-outward by the penetrating bullet. But this is done at a cost of translational or forward velocity of the bullet, which reduces the lethality by decreasing the number of organs that the bullet can penetrate and disable at any given point during the penetration.

Following the logic that the shape of a bullet is influential in determining its wounding capability due to rotation, images of the recovered bullets are presented below:

Considering handgun bullets such as 9x19mm Luger and 45ACP, the rotational component of the bullets movement will account for 5% additional kinetic energy loss in the target. This is small compared to the straight-line or translational motion of the bullet but it is still significant and can be enhanced with the optimum load selection, barrel twist rate and JHP design. In this way JHPs for handguns can be made more lethal once they reach the target and increased accuracy will also result from the increased stability.

Handgun cartridges with a higher muzzle velocity such as 357 Magnum could be combined with a bullet design similar to the PMC Starfire (with the lead protrusions on the face of the expanded JHP capable of moving against the gelatin like a paddle in water) and fired in a barrel with an unusually high twist rate for potentially greater use of the rotational effect for greater handgun lethality.

The choice of cartridges and barrels that are as long as found in practice was made in order to ‘bracket’ the results, make use of available user-donated funds and to encourage future study of dynamically-similar calibers such as 40S&W and 44 Magnum.