Your are correct that it is a 20th Century artillery projectile. It appears to be an armor-piercing projectile, from the WW1 to WW2 era. Without having super-precise measurement of its body diameter (such as, 2.96-inches), I cannot be more specific about the time-period than that.
I'll attach a photo at the end of this post which shows an Armor-Piercing 75mm projectile reported to be from World War 2 (but it may be WW1 era). Like yours, it had a WIDE copperbrass band about 1/2-inch above its base. The band is missing, indicating the projectile was fired and the copperbrass band tore off the projectile burrowed into the ground (or some other hard surface).
Some armor-piercing projectiles are Solid-Shot (meaning, not a hollow explosive body), and some have a solid "nose" with an impact-detonation fuse in the projectile's flat base. Your photos show the projectile in uncleaned condition, so I cannot tell for certain whether your projectile is a base-fuzed explosive one or a Solid-Shot. It LOOKS like it has a small hole in the center of its base, which is an indication that it is a Solid-Shot with a hole for the "tracer" chemical in its base. But that type usually does not have a groove encircling the hole. Please gently remove the dirt and rust-encrustation from that hole and groove. Then tell me the groove's diameter, the hole's diameter, AND how deep the hole is. A closeup photo of it after you clean out the groove and the hole would help give certainty in identifying the projectile.
Here is a diagram from a 1915 US Army document, showing a base-fuzed Armor-Piercing 3"-caliber shell at the top of the diagram.
Note that the diameter of the fuze in the 3-inch shell's base is about 1.25-inches. Most 20th Century artillery fuzes are brass, but a few are steel. At the moment, I think your projectile is just a Solid-Shot with a tracer hole in the base... but the groove around the hole makes me want to be sure it is not a base-fuzed explosive shell.
Where did you find that happy little life ender?
