The BL-20 was fully built in 2019, and entered official service in 2020 after an alert about an alien raid became official. At first, it fired HE rounds, which were completely useless against the technology the aliens used (which was entirely formed of drones), due to the powerful armour used by the force. Research was performed to find out more the drones that had been captured prior, and after it switched to a high-grade armour-piercing Single-Cal Round, it performed amazingly, and every Marine and SAS squad operated at least one BL-20.
Following the successful defence of Earth, the Marines started experimenting with different types of ammunition. An experimental laser shot was added, and worked well, but was extremely expensive.
When Earth was attacked again, the BL-20 was used. It was discovered that the BL-20 could neutralise drones instead of destroying them, and the drones were disabled from only a few shots from the sniper, and could be reprogrammed to defend Earth from more drones.