INVESTIGATION OF DESIGN FACTORS FOR STEEL GUN PRIMER TUBES
NAVAL ORDNANCE LAB WHITE OAK MD
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The Naval Ordnance Laboratory has determined the pressures required to rupture gun primer tubes of various designs. Design parameters investigated included the unvented length, the vent hole diameter, shape of the vent hole, the wall thickness and inside diameter of the primer tube and the amount of powder charge. The effect of variations in these design parameters on the pressure developed inside the primer tube also was determined. The results of the investigation indicate that primer tubes may rupture at pressures as low as 17,000 psi or as high as 53,000 psi, depending on the primer design. Primer tubes with either short unvented length or small vent hole diameters maintain peak pressures longer and rupture at lower pressures than tubes with longer unvented lengths or large vent hole diameters. The rupturing pressure increases with the tube wall thickness and decreases as the inside diameter of the tube increases. The peak pressure developed inside a primer tube is affected by the unvented length. The peak pressure is not significantly affected by the amount of unvented length when a partial charge, such as the tube 13 or 12 full, is used. Pressures simultaneously recorded at various positions in the primer tube indicate that a pressure gradient exists in the tube, the maximum pressure occurring in the vicinity of the first vent holes. Firing tests on tubes with transverse slots in place of round vent holes showed that for the same hole area the slotted tubes failed at lower initial pressures, presumably due to lateral forces exerted on the tube during firing.