Tungsten Billet for darts making actually is tungsten alloy billet because of the technical difficulties in manufacturing 100% tungsten.

Compared with brass billet or nickel billet, tungsten is more commonly used for darts manufacturing, the main reasons as follows.
High density:Tungsten has a specific gravity of 19.3(20 ℃) which almost the same as gold, so tungsten darts barrel is quite slimmer than other materials made barrel.
Abrasion resistant:Tungsten is abrasion resistant, so tungsten darts will be along with you as long as you expect.

Various sizes and contents of tungsten billet available here, popularly 70~90%, ranging from 14~18 gram and 18~40 gram respectively, and sometimes, 65% and 95~97% tungsten are offered if specific size or content is required.