During the initial product development of the M16 rifle in the 1960s, what critical manufacturing decision led to widespread malfunctions when first deployed in Vietnam?

The development of the M16 rifle represents one of the most significant military product innovations of the 20th century. After its introduction during the Vietnam War, this lightweight assault rifle transformed infantry tactics and became one of the most widely used military weapons in history. Test your knowledge about this iconic firearm's development journey and the controversies surrounding its initial deployment.

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Changing the ammunition powder without proper testing, which created excessive fouling in the chamber
Using aluminum instead of steel for the receiver to reduce weight
Adopting a smaller caliber (5.56mm) than the standard NATO round
Implementing a direct impingement gas system rather than a traditional piston system