When a flame from an ignited flammable gas enters the conduit and ignites the explosive pack, {HEAD ~ the bullet} is propelled into and frictionally engaging {TAIL ~ the inlet end} of the conduit body such that an internal passageway in the inlet end is substantially blocked to prevent the further propagation of flame upstream into the conduit 
frictionally engaging
When a flame from an ignited flammable gas enters the conduit and ignites the explosive pack , { HEAD ~ the bullet } is propelled into and frictionally engaging { TAIL ~ the inlet end } of the conduit body such that an internal passageway in the inlet end is substantially blocked to prevent the further propagation of flame upstream into the conduit
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