I've heard it's mostly due to either low strength, weapon skill or in the case of the Hunting Rifle and Survivalist's Rifle, faults in the model itself.
Crazy that everybody had serious bug issues with FNV except me(i had more bug issues with fallout 4 than FNV)
The oppressing feeling Fallout 3's tunnels had was so great, you felt like everything could pop at your head at any moments.
Fallout 4 is good, but nos as good as Fallout 3 and FNV