Your bullet is indeed a civil war era pistol bullet. It is either a .44 US Watervliet Arsenal bullet or a .44 Elam Potter bullet "for Army revolvers." Those two types of bullets look identical to the eye, but the Potter version is .73" long while the Watervliet is .05" longer, at .78-inch.
By the way... to my eye, the micrometer reading in the photo is slightly above .45-inch... which is correct for a cylinder-loading .44 Revolver bullet before it is fired.
Thank you Cannonballguy. It does read .459 I stand corrected on reading the micrometer wrong.
However none of the .44 caliber bullets measure .459 with the largest .44 measures .443 as shown by this chart for handguns.
The only old caliber that I can find close to .459 is the 45-70 or the .450 nitro express and both of those measure .458. What would be really helpful now would be to have the bullet weighed.
Gambrinus, the chart you posted seems to not tell the diameters of any civil war era pistol bullets. It appears to cover metallic-cartridge bullets from the Indian Wars era through the 20th Century. Non-metallic-cartridge civil war bullets tended to be larger in diameter. According to the "Handbook Of Civil War Bullets & Cartridges," the .44 Watervliet's unfired diameter is .455" to .456" -- and the .44 Potter's diameter is .452-inch. For dug civil war lead bullets (like Alan Payne's), add a few thousandths for the thickness of the lead patina... and you'll get the diameter result he got.
A few other civil war .44 revolver UNFIRED bullet diameters, from the Handbook:
.455" Colt Army "New Model".44
.455" Richmond Arsenal Colt .44
.458" Sage .44
.461" Starr 2nd Model .44
.462" Dean & Adams .44
.465" Kerr .44
.469" Starr 1st Model
Thank you everyone for you replies and info. I don't have a scale, have to put that on my list. I did take more pictures and made more measurements.
Bullet #3 may be of a different sort.
Bullet #1 .795 Long and .463 Wide.
Bullet #2 .820 Long and .456 Wide.
Bullet #3 is original bullet in post .788 Long and .457/.459 Wide
Last picture is most of what I found in this yard so far.
Other notable finds in this yard were Civil war Sword hanger from my other post 1840 seated dime and two 1863 IHPS. As you can see from the yard finds picture there were a lot of 1820 to 1840 artifacts. This area was active during second Seminole war in Florida.
Thanks again Cannonballguy, when I read "metallic cartridge" in your last post the light finally went on and bells started ringing. I found this picture which says these bullets are .44 Colt revolver (which matches the OPs bullet) and .44 Bartholow.