Again, here's my once-a-day post.
According to the "Handbook Of Civil War Bullets & Cartridges" your unfired bullet is a civil war Confederate .44 "Richmond Laboratory" (Arsenal) Colt bullet. Though its body-shape follows Colt's bullet design, it could be used in any of the various models of civil war .44 revolvers (Remington, Colt, Leech & Rigdon, etc).