Althought the term "Claymore mine" refers to pretty much any antipersonnel mine filled with bits of metal to create shrapnel, the official weapon is called the M18A1 Claymore Antipersonnel Mine. Not to contradict, but the Claymore is still in use today, by American forces in Iraq, as well as across the world, only because it has the capacity to be manually detonated with a triggering device, and such a weapon is allowed by international law. The mine itself is made of convex olive drab plastic with the words "Front Toward Enemy" printed across the front to eliminate confusion, and can be triggered in a host of ways, but most often by a trip wire strung from the mine across a path, in front of a foxhole, or a across doorway, or by the manual trigger.
The basic construction of the mine is as follows: The main body is made of plastic, inside of which is contained a layer of C4 explosive. In front of the C4 is 700 steel balls embedded in a layer of epoxy.
What happens: When detonated, the C4 charge propels the steel balls forward through the front of the mine in a 60 degree wide, 6.5 foot tall arc at approximately 4000 feet per second. Due to the speed and relative softness of the balls, they deform into bullet shaped projectiles that look sort of like small caliber firearm ammunition. The US Army states the optimum distance between mine and target is about 150 feet, as it gives the best damage to accuracy ratio, but the projectiles will travel several hundred feet further.
The main use of the Claymore mine is as a defensive weapon. During the Vietnam War, US soldiers set them up around the perimiter of their camps with overlapping fields of fire, so as to act as both an alarm and a deadly weapon. Inexperienced soldiers were often told that the Viet Cong would sneak up in the night and turn the Claymores around so that they faced into the camp, but this was more of a cautionary tale to make sure that everyone set up their mines right so no one got blown away while going out for a midnight bathroom break.
When used properly, the M18A1 Claymore Antipersonnel Mine is an extraordinarily effective weapon and defensive measure. Yes, it is painful, nasty, and deadly, but that's exactly what it is supposed to be, and it gets the job done.