Your artillery projectile fragment is definitely from a civil war yankee 3.8"-caliber James shell. That type was used in combat from 1861 through 1863, when it fell out of favor due to performance failures. Civil war artillery projectiles are given the inventor's name, if it is known. In this case, the inventor was Charles Tillinghast James.
All of the James explosive shells had an impact-detonation fuze. So, there should be some "dud" ones in the very-nearby vicinity. Don't worry about digging an intact one, because excavated 1860s artillery shells are NOT dangerous to merely handle, or even to drop on a concrete floor -- unlike 20th-Century artillery shells. Please see the "About me" info in my Profile.
Listen for a deep iron signal on your detector. Fired James 3.8"-caliber shells can be anywhere from a few inches to 4 feet deep.
Here's a photo of an intact one.