that the drill bit cannot readily penetrate. This version uses four ceramic bullets, which shatter upon impacting the rock, and which in turn are intended to fracture the rock to allow the drill bit to proceed. The tround is designed such that each projectile impacts the target at a slightly different time, imparting multiple shocks to create constructive interference of the shock waves in the target material. Dardick firearms The Dardick firearms were essentially revolvers whose unique open chambers could be reloaded from a magazine. The operating principle used was the same as a double-action revolver, with a long trigger pull serving to rotate the cylinder, cock, and release the hammer. Since the commercial trounds had the same exterior dimensions, the same firearm action would, by using a different barrel, chamber any of the calibers the trounds were chambered in. The Dardick Model 1100 had a 10-tround magazine, and was only available chambered in .38 Dardick Tround (9 mm). The Model 1500 came with interchangeable barrels, and was available in .38 (9 mm), .30 (7.62 mm), and .22 (5.56 mm) trounds, with a carbine conversion kit also available in .38 and .22. The Model 1500 could be configured to hold 11 or 15 trounds, and came with 4- or 6-inch barrel lengths. A Model 2000 with a 20-tround capacity is also reported to exist. All versions used a non-removable magazine, which could be loaded with stripper clips or one round at a time. The Dardick revolvers proved to be a commercial failure, despite being, in the words of one reviewer, "as versatile as a six-armed monkey". References External links Pistol and rifle cartridges