Mach wave Mach wave In fluid dynamics, a Mach wave is a pressure wave traveling with the speed of sound caused by a slight change of pressure added to a compressible flow. These weak waves can combine in supersonic flow to become a shock wave if sufficient Mach waves are present at any location. Such a shock wave is called a Mach stem or Mach front. Thus, it is possible to have shockless compression or expansion in a supersonic flow by having the production of Mach waves sufficiently spaced ("cf." isentropic compression in supersonic flows). A Mach wave is the weak limit
.17 Mach IV .17 Mach IV The .17 Mach IV is a wildcat centerfire rifle cartridge, based on the .221 Remington Fireball case, necked down to fire a .172 bullet. The cartridge was introduced in 1962 by Vern O’Brien. The cartridge offered an easy case conversion and good ballistics, but could not compete against the .17 Remington. The name, Mach IV, comes from the claim that the bullets can reach 4,000 ft/s. Due to the relatively small case capacity, even small variations in powder of can lead to the difference between a safe and dangerously over pressure load. The .17 Mach IV became