A well-built AR-15 is one of the most reliable semi-auto firearms available. But sometimes even the best rifles may malfunction, and when they do, it is time to diagnose the cause of the malfunction.
One of the first components that should be investigated is the magazine.
Magazines get dirty. They vary in quality and dimension from manufacturer to manufacturer. Springs wear out and bodies get bent or broken. Magazines get dropped on the ground and stepped on. Most AR-15 malfunctions are related to lube, ammo, or magazines, or a combination.