Actually... it isn't a Colt bullet. The highly-respected "Handbook of Civil War Bullets & "Cartridges" says that although your bullet was made for use in Colt .44 revolvers AND "other holster revolvers", it is not from a Colt bulletmold. It was manufactured by the Elam O. Potter firm during the civil war. It is a bit shorter and lighter than the similar-looking Colt "Old Model" .44 bullets. The measurements you thoughtfully provided for us (thanks muchly) match up with the Handbook's measurements for the Potter-made bullet.
In the handbook, your .44 Elam O. Potter bullet is shown as bullet #9. The similar-looking longer version for Colt and other revolvers was made by the US Watervliet Arsenal. The "New Model" Colt .44 bullet (with one body-groove above the rebated solid flat base, which is made by Colt bulletmolds) is shown as bullet #32. Note, there is a similar-looking variant of the Colt New-Model .44 bullet, made by H.W. Mason SLIGHTLY AFTER THE CIVIL WAR ended. (See the Handbook's bullet #34.) The Mason .44 bullet for revolvers has a "noticeable large sprue" on its flat base.