I found this at Hilton Head Sc and would like to know how old it is. It is 2.5 inches, heavy and doesn't appear to have been shot. Thanks, this is my first post.
2.5 inches means it's probably a 50 cal FMJ. It's not a cartridge, it's the projectile out of one. The lines on the sides are the barrel rifling marks which means it was most definitely fired. Age is impossible to determine, some time from the last 100 years.
I live in the Hilton Head area, and this is a long shot (pun intended) but maybe a stray bullet from the Marine Corp base, Parris Island, it's only about 4 miles away from Hilton Head's north shore, what part of Hilton Head did you find the bullet?
It does look to be older rather than recent and looks like it been partially in the salt water.