The .17 MACH IV is a small-caliber, high-velocity rifle cartridge. Developed in the early 1970s by Vern O’Brien, it is based on the .221 Remington Fireball case, which is necked down to accept a .172-inch (4.37 mm) diameter bullet. The cartridge is known for its flat trajectory, low recoil, and high velocity, which typically exceeds 4,000 feet per second (1,219 meters per second).
The 17 MACH IV is popular among varmint hunters and target shooters due to its excellent accuracy and ability to effectively eliminate small game at extended ranges. Its low recoil makes it easier to spot impacts through the scope and adjust accordingly. Despite its performance, the cartridge has remained more of a niche choice, overshadowed by more widely used rounds like the .17 Remington.
Reloaders favor the 17 MACH IV for its efficiency and ability to handload to specific needs, though commercial ammunition for it is scarce. If proper safety measures are taken, the cartridge offers impressive performance in small game and varmint hunting scenarios.