Pinkies don't have teeth or nails and the snakes know they don't pose a threat. When meals are too small, then the snake won't constrict. Why is he still on pinkies? Baby Ball Pythons right out of the egg can eat hopper mice, then by the 3rd meal or so, they can go on to small adult mice. Pinkies aren't much of a meal and he's likely wasting more energy swallowing them than he's getting out of them. Try a small adult mouse, he should be just fine.