This specification outlines the basic performance requirements and corresponding test methods for barrel blocking devices used in the sport of air soft. It covers air soft gun barrel blocking devices that may be inserted or otherwise function to prevent an airsoft projectile from leaving the muzzle or the confines of the barrel blocking device. The performance requirements and test methods are intended to provide a reasonable degree of safety in the normal use of barrel blocking devices in air soft guns. The specification describes the barrel blocking device retention test that must be performed to ensure that the barrel blocking device will remain in or over the barrel and prevent an air soft projectile from exiting the muzzle or the confines of the barrel blocking device. It also requires the inclusion of a user's manual outlining the proper installation and usage of the device.