Apparently, you did not bother to read the instructions posted at the very top of this forum. ("Please read before posting items in What-Is-It".) Accurate measurements are very often crucially necessary to figure out the correct ID of a mystery-item. And for bullets, SUPER-accurate measuring (in hundredths-of-an-inch) is necessary... because bulets come in .40, .41, .44, and .45 caliber.
Despite your ignoring of the instructions, I'll do what I can to help you. Without measurements, I'll have to guess that the ring is between 3/4" and 1" in diameter. Comparing it with the bullet, I'll also have to guess that the bullet is either a .44 or .45 caliber. (But it might be a .38 caliber.) Its length is short in comparison to its width, so it is most likely for a pistol rather than a rifle.
The exact shape of a bullet's grooves is important for correctly identifying it. But the grooves in your bullet have not been thoroughly cleaned out. I think I see some tiny very-short parallel lines in your bullet's grooves. If they really are there, instead of being dirt-grains, your bullet has what is called a "reeded groove." (See the photo which I will attach below.) Bullets did not have reeded grooves until (approximately) the 1880s ...and many bullets made today still have reeded grooves. So, IF your bullet has reeded grooves, it can't be from any early than the 1880s and could be from anytime in the 20th-Century.
