Damage numbers and how they work

I have similar issues that are more common than they were since the game was released. The only time that I have one shotted a player was with a headshot with a Kraber or a headshot with a Peacekeeper, though I'm sure I would be able to do the same with a Mastiff. However, I see people shoot once or twice and down me instantly even with full HP and armor, including a high tier headpiece. People are hacking and the scores they show often are absurd numbers. It's getting annoying real fast.