DOES all normals have.....

[Inknsteel]

Those would be way too big, he is tiny. His neck is smaller than my pinkie.

You don't go by the width of the neck. You should be feeding your bp one prey item about as big around as the girth of the thickest part of his body. Snakes unhinge their jaws and stretch around the prey. I think you should be fine to up the prey size to adult mice, at least small adult mice...