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Although the need for a railgun bore lifetime metric has been establkhed for some h e , to date there have been no serious attempts to quantify the anticipated lifetime of a railgun bore surface. The Air Force (AF) Is meeting this challenge with an in-house bore lifetime experiment that compares four different bore insulator materials and lay-ups in a controlled test environment. Initial testing has established a G-9 material as a baseline for comparison. Each of the four insulator test series consists of a low current checkout shot followed by a ten shot series of plasma armature firings with peak pressures of about 30 ksi and currents on the order of 750 U. The test sequence produces erosion that is easily measured both as bore growth during the test series and as post-test component mass loss. Typically, the rails lost almost twice as much mass as the insulators, but volumetrically, about three times more volume of insulator material was removed compared to eroded volume of copper from the rails. The loss of copper from the rails is highly non-uniform, as might be expected in a round bore railgun. Mass loss and bore growth data from all four insulator test series are compiled as a gauge of bore lifetime. The railgun performance on a typical shot isTEST SERIES 1 TEST SERIES 2 TEST SERIES 3 TEST SERIES 4 Fig. 1. Laminate orientations for all four types of insulators testedmeasure the bore diameter as a function of axial location in the barrel after every shot. Measurements were recorded for diameters from rail to rail and from insulator to insulator. Second, all of the bore components were weighed before and after the test series to determine the total material mass loss from each eleven-shot test series. Finally, selected dimensions of the bore components were measured after each test series to study the uniformity of material removal. TEST SERIES SUMMARYgiven along with a tabulation of the coarse shot parameters for each test in all four series.The 25 mm LTS railgun has been successfully operated on three previous test series to study the thermal loading in

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