2018 Insensitive Munitions & Energetic Materials Technology Symposium
Portland, OR
Gun Launch and Setback Actuators
Ernest L. Baker and Michael W. Sharp
Munitions Safety Information Analysis Center (NATO), Brussels, Belgium
There is currently no agreed standard methodology for assessing the suitability of
explosives for gun launch or for the determination of acceptance criteria for explosive fill
defects. Laboratory setback activator testing has been used as an assessment tool for
investigating the suitability of explosives for gun launch. Unfortunately, laboratory
setback activator testing is not standardized and large variations exist in activator
design, function and results between different laboratories. However, it is the only
currently available tool for assessing an explosives safety and suitability to launch-
induced setback forces. In laboratory setback activator tests, ignitions are observed at
setback loadings that are much higher than produced in actual gun launched projectiles.
This may be related to the defects in actual projectiles, which appear to be very different
than the laboratory tests.
INTRODUCTION
A major safety concerns for energetic materials present in gun launched munitions is the
exposure to severe set-back forces which develop as the shell is accelerated. Table I presents a
listing of typical projectile accelerations associated with different gun launches [1,2]. Under these
conditions, energetic materials have been observed to occasionally react prematurely. The term
in-bore premature is used for the explosion of a munition whilst it is still travelling down the barrel.
This is not a new phenomenon and a number of nations have developed laboratory setback
actuator testing that can be used to understand ignition mechanisms for energetic material when
exposed to an acceleration environment. However, these capabilities appear to be used mainly
for research purposes and there is little evidence that they are mandated as part of a nation’s
formal qualification assessment process. None are included in NATO Standards on qualification
of energetic materials.
TABLE I. PROJECTILE MAXIMUM ACCELERATIONS AND PRESSURES
Gun System Max Projectile Acceleration
Range (kGs)
Max Chamber Pressure
Range (MPa)
Artillery 4-30 70-500
Mortars 1-13 20-140
Tank Guns 25-120 200-830
Medium Caliber 50-200 140-1400
MUNITION SAFETY ASSESSMENT PROCESS
The development of explosives requires a rigorous regimen of tests, both small-scale, and large-
scale, before explosives can be judged safe and suitable for service use. NATO nations have
agreed that all energetic materials be qualified in accordance with NATO STANAG 4170, with
guidance provided in the associated AOP-7. Final or Type qualification is the process by which
the safety and suitably of energetic material for its intended application and role are assessed. A
