Recent experiments with relatively high action armatures in a medium caliber launcher (35-mm rail height) have shown a repeatable vibration in the armature which is observable in early parts of both the recorded muzzle voltage and on the contact surface of the rail. Although the vibration or "chatter" in the contact does not appear to grow in amplitude or shift in frequency during this early part of the launch, it is probable that it plays a role in conditioning the armature surface for later transition in the launcher. This paper examines the recorded test data and compares it with structural analyzes of the launch package to show that the chatter is correlated with natural vibration modes in the armature. Probable causes of chatter are discussed and tests incorporating some potential solutions are presented. Reduction or elimination of this behavior is important both for long-term bore life of the launcher and maximum launch package performance with payloads that are sensitive to lateral launch loads.
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