The 12.7 x 99 mm High Pressure (HP) round, marked with a yellow tip, is specifically designed for testing and proofing weapons rather than combat. These rounds are used to ensure the structural integrity of weapon barrels and components under extreme pressure conditions during manufacturing and maintenance. Fired in specialized test rigs or heavy machine guns like the Browning M2, the HP round is crucial for quality control, ensuring that military-grade firearms can withstand the rigorous demands of combat environments.