with each failure generally ending the program that had it. Variations of igniter venting, ignition energy and chamber configuration can make the ignition more reliable, and the pressure profile more predictable. However, as of the 1993 survey by Knapton et al., no designed, hydrodynamic models of BLP guns had actually been validated. Tactically, there can be widely varying accuracies in range, exactly the opposite of one hoped-for tactical advantage. The best systems report 1 to 1.5% single standard deviation (i.e. large) variations in the throw. Over 40km ranges, this is a 150m irreducible error. The failure of the last firing of the Army Research Lab 120mm BLP gun, with the hydrazine mixture, was attributed to incomplete ignition. The post-firing review found that a failure of the foil in the ignition charge vented ignition gases via the igniter, as well as into the propellant. The poorly ignited charge moved the projectile partially down the tube, increasing the surface area of the propellant. The increased surface area of the propellant then ignited in the tube, raising pressures in parts of the gun not designed for them. The large overpressure caused "catastrophic tube failure" (an explosion destroying the gun tube). In 1977, the Naval Weapons Center tested the 25mm bipropellant nitric-acid/hydrocarbon gun. At one point, "too fine" a mixture caused a catastrophic failure. In 1981, under a DARPA contract, Pulse Power Systems Inc. performed substantial development of a high-performance automatic 75mm BLP gun using NOS-365. Round 205 had an apparent high order detonation of the propellant, which was thought impossible. Metallurgic examination of the tube fragments determined that cumulative damage may have occurred from overpressures of earlier rounds. Examination of the pressure profile of Round 206, which had another catastrophic failure, showed anomalously low pressures followed by a pressure spike, which appeared to be the burning of a bubbly froth of monopropellant that transited to a detonation as the pressure increased. This was attributed to poor procedures to handle and pressurize the fuel. References Further reading Artillery