The sound depends upon what has caused the misfire. If the primer is not ignited, the only sound will be a loud click as the firing pin strikes it. If the primer ignites but does not ignite the powder charge (which may be absent) the only sound will be a loud 'POP". If the primer ignites an insuficient powder charge (some fraction of what the normal charge would be), there will be a muffled "BANG" of much less intensity than a full charge. An experienced shooter will be able to hear and determine any of these misfire conditions.
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