Erosion observations on recovered large caliber armatures

A unique feature of the Kirkcudbright EML facility is its ability to fire over an open range. The primary purpose of this is to enable projectile firings at target distances of up to 2 km. An additional benefit however, is the ability to recover fired items. It has now become normal practice to follow a day's bring with a thorough down-range search. Despite the rough terrain, around 70% of all 90 mm armatures are recovered. Most of these armatures are intact with little or no ground impact damage. Examination of recovered armatures has proved an invaluable aid to armature development and optimization. Over the last few years, our 90 mm armature design mass has dropped from around 1.2 kg to 800 g, despite ever increasing energy levels. Previous analysis efforts have concentrated mainly on surface phenomena and hot zones within the bulk of the armature material. This paper examines material loss, which frequently amounts to around 10% of the total armature mass. With a large quantity of recovered armatures available, data exists to enable correlation with various firing parameters. This process provides an insight into the nature of armature erosion and assessment of the relative significance of heating mechanisms. Muzzle kinetic energy and post-transition charge transfer both enable mass loss to be quantified with a typical accuracy of around 7%.