How the US Army refined its battle-tested, controversial M4 Carbine for modern combat

• The US Army upgraded its nearly 500,000 M4 carbines to more lethal and higher-tech M4A1 rifles.
• The M4 became controversial due to costly manufacturing and reliability issues like weapon jamming.
• The M4A1 has a heavier barrel, improved accuracy, and compatibility with better-performing ammo.

Meet the M4 Carbine: Over the course of many years, the US produced hundreds of thousands of battle-tested, upgraded M4A1 rifles engineered to more quickly identify, attack, and destroy enemy targets with full auto-capability, consistent trigger-pull, and a slightly heavier barrel.