That is a Thompson Center Hawkins .50 caliber with a 28 inch barrel that is 15/16th on the flats. It has a 1-48 twist barrel and will shoot roundball, conical, and in some cases sabots. I would try 90 grains of Pyrodex Rs and a patched .490 roundball. A very nice rifle.

If you want a ramrod, Cain Outdoors sell Super Rods in 28 inches that cannot be broken, you will need a cleaning loading jag, a short starter, and some other things. You have a great rifle for hunting, shooting, and passing down to your son.