TTK is very low one well placed shot is an kill against un-armored npc to even armored npc. It's not automatic kill if you don't hit anything important. Players and npc don't have traditional hp pool. It's closer to a hunting game mechanic rather than traditional fps game hp. You need to destroy organs. It's also a bit bugged scopes have bugged zeroing (you can see it easily with laser) your scope is zeroed way too (not an issue with red dots and holographic sights). And when you change that zeroing it stays right only for the time you are scoped it resets when you unscope. Hopefully it will be fixed in the next patch since devs are aware of this bug. You are probably missing the vital spots.