It is another fired civil war .44 revolver bullet. It appears to show the 7-groove rifling marks from the bore of a .44 Colt Revolver. Compression from firing, and the rifling-marks, have wiped out most of that bullet's identification characteristics -- but I see a tiny remnant of one body-groove, so it is either a fired yankee Colt or Hazard, or a Confederate "Richmond Laboratory" bullet.
If you look very closely, you can see a small circular indentation around its "nose," which is the imprint of the conical-shaped "mouth of the Colt Revolver's bullet-rammer. By the way, that rammer-mark is also visible on your fired CS "Richmond Laboratory" bullet, in your bullet-post #17.)