The MARCK-15, also known as the “Hydra”, is the base system for everything associated with the Hydra® Modular Weapon System.  This configuration of the Hydra is setup as a 5.56 x 45.  It includes the Hydra® Modular Lower Receiver with an AR Magazine Well, an AR Magazine, the Hydra® Quick Change Barrel Upper Receiver (QCB-D), a 16-inch 5.56 Barrel with a Low-Profile Gas Block, underneath an 11.5″ transformable handguard. A Hydra® Modified Bolt Carrier with a 5.56 Bolt and Firing Pin, the Hydra® D-Fender D-Ring for increased reliability, and a B5 systems stock and pistol grip. With this base rifle, you can purchase and utilize the rest of an ever-growing system including our various magazine wells and caliber conversion kits.  To convert this system to another caliber, the most you will need to change is the barrel, bolt, and magazine well to the desired caliber.  For some calibers, simply changing the barrel and bolt on this weapon will allow you to fire multiple calibers.  This includes. 350 legend, 300 Blackout, .450 Bushmaster.  This weapon system continues to grow and become the most versatile Black Rifle platform the industry has ever seen.