Figure 2.

Example of a modern controlled expansion projectile, 9 mm Parabellum, lead free, Action-5 bullet (RUAG Ammotech, Laxenburg, Austria). Vi is velocity at impact. Modern controlled expansion bullets have a velocity operational range wherein they perform as designed. Image 1 is the pre-fired bullet (6.1 g, 94 gr). Projectiles 2 to 9 were accelerated in stepwise increasing velocity (energy) and retrieved from ballistic gelatin. Bullet 3 is subsonic and 4 at 349 m/s is supersonic (at 20°C the speed of sound in air is 343 m/s). Bullets 6 to 8 display good expansion, 1.5 to 1.61 times the 9 mm original diameter. Bullet 9 was accelerated to a speed that exceeded the engineering integrity of the projectile design and the expanding metal was torn away decreasing the wounding potential and increasing risk of over penetration (40).