Washington: While political attention in the United States last week was focused on Hillary's emails and the Republican Party's attempts to derail nuclear negotiations with Iran, the National Rifle Association enjoyed yet another victory.

This time America's most powerful lobby group managed to block a move to ban the free sale of armour-piercing bullets for handguns.

A move to ban green tip, cop-killer ammunition for pistols has been scuttled with the help of the NRA. Pictured: M855 5.56mm ammunition for rifles. Credit:AP

The so-called green tip ammunition – which is designed to pierce helmets and body-armour – has long been legal in America for use in AR–15 rifles. These are the military-style semi-automatic rifles that have become the most popular hunting and self-defence weapons in the nation after their high-profile use in the massacres in a Sandy Hook primary school and a Colorado cinema.

The so-called M855 round, also known as the "cop killer", is now the second most popular ammunition for use in America's most popular rifle.