the designs are, however, common in designated light armor-piercing small arms ammunition. Discarding sabots such as are used with M1A1 Abrams main gun are more commonplace in precision high-velocity gun ammunition. Mining and foundation drilling Tungsten carbide is used extensively in mining in top hammer rock drill bits, downhole hammers, roller-cutters, long wall plough chisels, long wall shearer picks, raiseboring reamers, and tunnel boring machines. In these applications it is also used for wear and corrosion resistant components in inlet control for well screens, sub-assemblies, seal rings and bushings common in oil and gas drilling. It is generally utilised as a button insert, mounted in a surrounding matrix of steel that forms the substance of the bit. As the tungsten carbide button is worn away the softer steel matrix containing it is also worn away, exposing yet more button insert. Nuclear Tungsten carbide is also an effective neutron reflector and as such was used during early investigations into nuclear chain reactions, particularly for weapons. A criticality accident occurred at Los Alamos National Laboratory on 21 August 1945 when Harry Daghlian accidentally dropped a tungsten carbide brick onto a plutonium sphere, known as the demon core, causing the subcritical mass to go supercritical with the reflected neutrons. Sports usage Trekking poles, used by many hikers for balance and to reduce pressure on leg joints, generally use carbide tips in order to gain traction when placed on hard surfaces (like rock); carbide tips last much longer than other types of tip. While ski pole tips are generally not made of carbide, since they do not need to be especially hard even to break through layers of ice, rollerski tips usually are. Roller skiing emulates cross country skiing and is used by many skiers to train during warm weather months. Sharpened carbide tipped spikes (known as studs) can be inserted into the drive tracks of snowmobiles. These studs enhance traction on icy surfaces. Longer v-shaped segments fit into grooved rods called wear rods under each snowmobile ski. The relatively sharp carbide edges enhance steering on harder icy surfaces. The carbide tips and segments reduce wear encountered when the snowmobile must cross roads and other abrasive surfaces. Car, motorcycle and bicycle tires with tungsten carbide studs provide better traction on ice. They are generally preferred to steel studs because of their superior resistance to wear. Tungsten carbide may be used in farriery, the shoeing