It is a 50. You have to measure below the crown. If it is the Hawkins made by TC or CVA, they did not make a .52. Start with a 490 roundball and .15 patch. See how that grabs the rifling Should be tight but not so hard that you cannot push it down with reasonable force. Never hammer a ball. Sometimes guns prefer a 495 ball and .10 patch. Experiment and see what works for you.
GBJ