I tend to agree with PDQ on this one. Even though 50 pounds is a relatively light draw weight I still think that 4 grains per pound is too light. Ofcourse, that is also going to depend on your draw length. If you are shooting the bow at under a 26 inch draw length then it might not be as much of an issue as there is less energy being released into the bow.

Regardless, I would stay at least at 5 grains per pound of draw weight which would give you a total arrow weight of 250 grains.