In order to answer your question as to why Hunters die to a single Pistol shot to the back, I will explain:
First an foremost, you have to realize that Hunters are giant colonies of orange worms. Yes, you heard correctly, worms.
Next, the armor of the hunters and their shields are made of the same material as the Covenant flagships (Thus extremely durable.)
Now, to get to the main point: Why Hunters die to a single Pistol/Sniper Shot.
When you fire the high-caliber, high-velocity rounds, they tear through the worm colonies and hit the armor from the inside. The velocity causes the rounds to recochet multiple times, shreding the colony. Eventually, there are too few worms left to hold the Hunter's armor's weight and the last of the colony is crushed by the 2-3 ton armor.
I hope that you have been informed ^_^
Now, I must watch you escape from the building where the Silent Cartographer is. So far, your "Ragequits" have been most humerous :P
haha, as a broke college student, I don't have the money for Halo4 >_>
However, Halo Reach is keeping me satisfied at this moment. I've also started a Nuzlocke Roulette. MVP is currently a Magcargo. NU my rear. He's saved my hide more times than not and will instrumental to Lenora's defeat O_o