i would say carved Minie ball but for the purpose. ??? In Georgia peaches were king one time, and old timers just took peach seeds of the freestone variety and carved little baskets out of them. my daughters used them with Barbie dolls lol when my Dad did some.
may have been out of boredom. i have a minie carved into a point with a slit and is believed to be a chess piece bishop. but that i have never seen. there was a reason
BUT it could have been a musket nipple protector used by a string attached to protect the nipple on the musket from dirt and water. most are smaller flatter, but I could see that maybe...the base of the minie being hollow. there were 3 ringers, two ringers, solids etcc huge variety. with and wiithout cavities. some had wooden plugs, some 69 caliber common in Va theaters of war, not just 58 caliber.
i would consider musket nipple protector albiet big cavity.