One Bullet Per Second, I Am Learning to Rebel in the Last Days

[After the end of the world + wasteland + no rebirth + no harem] A hundred years after the end of the world, the surviving humans moved to the underground city and initially established a new social order. When Xu Bufan traveled through time, he faced not only the oppression of the upper class, but also the crisis of mutant creatures. Fortunately, he has a system that allows him to earn one point for every second he survives, which can be exchanged for various types of ammunition and weapons. In order to protect himself, he had to rely on equipment to resist. Raise up the pole and respond to one call. When the superior master of the underground palace thought that they were still a group of underground refugees who could be manipulated at will, they had already become a large army with the blessing of Xu Bufan! The underground palace changes owners, order is established, and new life begins. When other dungeons put pressure on him to compete for resources, don't be afraid, I have a level 3 weapon civilization! Don't be afraid when mutated creatures grow into monsters, I have a new century mecha! As soon as the ancestral god-level mecha comes out, monsters from other worlds will also get it!