Abstract:
Ammunition loaded into large calibre gun chambers, which have been heated by
previous firings, can enter a hot-gun state; conservatively defined as hot if 50 rounds or
more are fired in a four-hour period. In this state the temperatures of the explosive fill,
such as Composition B, may easily exceed their qualification temperatures. This is
potentially dangerous if the weapon misfires either by cook-off or premature shell
ignition. Currently there are no standard tests that can be used to assess the behaviour of
Composition B filled munitions in a simulated hot-gun condition.
During firing some of the energy can be transferred to the explosive fill. Defects induced
by melting and/or re-solidification of the Composition B will lead to a greater chance of
accidental initiation of the explosive due to setback forces creating hotspots and ultimately
resulting in an accidental in-bore explosion. The aim of this research was to investigate
the conditions of this accidental initiation of Composition B in a hot gun situation at the
time the projectile is likely to be cleared from the gun. It investigated whether this
situation can be simulated cost effectively by examining the sensitivity of Composition B
samples that were thermally conditioned in accordance with calculated temperature-time
profiles. A target assembly was designed to mimic setback forces by using projectile
impact. A series of tests conducted on these composition B filled targets, which had been
subjected to hot gun conditions, were performed at the Cranfield Ordnance Test and
Evaluation Centre (COTEC) to simulate setback effects at shot start. Mechanical energy
was delivered by an impacting sabot launched from a nitrogen gas powered gun. Post
firing simulation and analysis of materials were used to determine the mechanism of
initiation and the severity of the event compared to the amount of force the samples were
subjected to.
