New Frontier Armory’s (NFA) C-5 ARs are not just another Colt clone. These guns run MP5 magazines. The big advantage to this is that the MP5 magazines are a true double stack magazine, feeding from both sides. This makes them run great in AR carbines and rifles.
I have been working with Pistol Caliber Carbines (PCC) since the Colt SMG. The Colt magazines were hard to load and prone to failures. I have always liked being able to shoot economically and train on pistol rated steel targets. PCCs have gotten steadily better over the years and I think the C-5 may represent the pinnacle of their evolution.