New In Box, Old Stock What is now Hydra Weaponry was MGI Modular Weapons System. Available from MGI is this Marck-15-22lr is an AR Conversion kit complete with a 22lr and 556 quick change system. A new in box unit is available. Also known as the Hydra 15, the unit is a complete 22 LR AR Package and the accompanying 556 upper kit and includes a new Rise Armament Nickel Boron BCG. A MGI Bolt and Firing pin is also included in the package and one magpul magazine