When you post something like that it would help if you give the size of it,maybe put
a coin in the photo with it.So people can get an idea of the size.If it is around a 39 cal
I would say it is a Tranter Revolver bullet ID # M&M 90,In the McKee and Mason bullet
book.
That is the same ID# M&M 90 but McKee & Mason called it Tranter Revolver.A Lemat Revolver
bullet is ID# M&M 658 (one type).But if you scroll down on this site it has a Lemat Revolver Bullet that is unlisted in McKee & Mason bullet book and Looks like the one on the other link but no M&M ID#.But,that is a very nice bullet that you found
I still can't get a close caliber size could you put a ruler under the bullet,so we can see the diameter
of the bullet.From what I have gathered about the LeMat Revolver and the Tranter Revolver bullets
they range from 39 to 44 cal. that are listed in McKee and Mason bullet book.The LeMat Revolver also had a single shot barrel that shot a 65 cal 18 guage shotgun.Check out these links.
looks 44 ish cal to me (a half inch is 50 cal --this one is a bit under that size) -- its a pistol round-of the old blackpowder type commonly used during the CW time frame era ---clearly its never been fired --so it is a "drop" or dropped bullet -- nice find
the LeMat or Tranter bullets that the others speak of are good matches for this round *and both were civil war era type weapons ---now weither or not this exact bullet is "civil war" related is a differant matter*-- it depends on weither there were troops in the area where it was found (say a camp site) or battles fought there / target shooting ) or if the area is on the line of march to from other civil war places --all this factors in --since this could be a ---pre war --war--or post war --dropped bullet --- knowing a bit about the area's history where it was found might help you answer that question.