Nursing vs. pumping

Is it possible to produce enough milk for your baby but not be able to pump enough? I can nurse my baby and when i hand express i get plenty of milk. If i use my manual or electric pump i dont get much. I get barely half an ounce. Ive tried switching flanges sizes and ive tried different settings on the pump. Anyone had the issue of not getting milk with the pump. I dont understand why thats happening.