Whose Immortal Weapon Is an Automatic Pistol?

The protagonist was once a battle-hardened special forces soldier who died unexpectedly during a dangerous mission. His soul transmigrates to a wondrous world of immortals and martial heroes, where everyone is born with a personal magical treasure. His turns out to be a 9mm semiautomatic pistol with unlimited ammunition. Haunted by his past-life experience, he is terrified of dying again, so he treads carefully on his path to immortality and often wins through ambushes.