There were more than a few different types of .50 BMG ammo made. They include:
Cartridge, Caliber .50, Ball, High Pressure Test, M1
Cartridge, Caliber .50, Blank, M1 (no bullet, crimped)
Cartridge, Caliber .50, Incendiary, M1 (blue tip)
Cartridge, Caliber .50, Tracer, M1 (red, maroon, or orange tip)
Cartridge, Caliber .50, Blank, M1A1 (no bullet, crimped)
Cartridge, Caliber .50, Ball, M2
Cartridge, Caliber .50, Ball, Armor Piercing, M2 (black tip)
Cartridge, Dummy, Caliber .50, M2 (holes in case)
Cartridge, Caliber .50, Ball, Armor Piercing Incendiary, M8 (aluminum tip)
Cartridge, Caliber .50, Tracer M10 (red, maroon, or orange tip)
Cartridge, Caliber .50, Tracer; M17 (red, maroon, or orange tip)
Cartridge, Caliber .50, Ball, Armor Piercing Incendiary-Tracer, M20 (red ring/aluminum tip)
Cartridge, Caliber .50, Incendiary, M23 (blue tip)
Cartridge, Caliber .50, Ball, M33
Cartridge, Caliber .50, Ball, Spotter-Tracer, M48A1
Cartridge, Caliber .50, Ball, Spotter-Tracer, M48A2
Cartridge, Caliber .50, Ball, Plastic Practice, M858
Cartridge, Caliber .50, Tracer, Plastic Practice, M860
Cartridge, Caliber .50, Saboted Light Armor Penetrator (SLAP), M903 (plastic sleeve on projectile)
Cartridge, Caliber .50, Saboted Light Armor Penetrator-Tracer (SLAP-T), M962
Cartridge, Caliber .50, Ball, Practice, T249E2
Cartridge, Caliber .50, Ball, High Pressure Test, T251
Cartridge, Caliber .50: Armor Piercing Incendiary (API), MK 211 MOD 0
The most spectacular round used today is the .50 cal BMG Raufoss round.
This is an incendiary explosive round usually marked with the Raufoss headstamp and a white tip, althought the US Navy uses the tracer version of the round with a white over red or green tip. When this round strikes a solid target, there is an incendiary flash, a bang and a lot of white sparkles from the zirconium. Fun stuff!