Your bullet's caliber (about .45) and its form indicate late-1800s manufacture. Its length indicates it is a rifle bullet, not for a pistol. I cannot find an exact match for it, but the closest is an 1882-pattern Maynard bullet. See the image below.
I was tempted to call it a .52 ringtail Sharps but the nose on your bullet is more rounded. I'm thinging your bullet is more modern than CW period. Just my opinion. Nice find.