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Last week's mass-shooting at a cinema in Colorado has - not surprisingly - intensified America's bitter and long-running argument with itself about gun control.

The argument is political and highly partisan. But it is also practical: would tighter gun laws actually lead to fewer gun deaths? You might think it's obvious that they would. But it seems the evidence isn't quite that clear.

Also: how have Olympians changed in the last century?

(Image: Shell casing for .40 caliber cartridges. Credit: Getty Images)