The SureFire Blank Safety Device not only cycles the host weapon when using blank ammunition, but is designed to safely contain up to three inadvertently fired live rounds of M855 without injuring the shooter or others. The BSD duplicates the weight, length and feel of its equivalent SureFire sound suppressor which is critical in providing realistic training value. If a live round is fired, the live round penetrates a sacraficial wall, causing sound and flash to vent from the bottom of the BSD and alerting the shooter and those around him of a problem. The SF-BSD-556 is specifically for 10.5-inch barrels such as the MK18, while the SF-BSD-556-M4 is for 14.5-inch barrels. The Fast-Attach mechanism allows for secure attachment or removal of the Blank Safety Device to SureFire compatible adapters, no tools required.