It's an oldie but not necessarily CW era. Remember most CW rifles were sold as surplus after the war as our government switched over to breech loading arms and many of those CW guns were used for hunting well into the late 1800s-early 1900s. The poorer folks used these muzzle loaders for many years after the war as they killed game quite well and cost a whole lot less to shoot than metallic cartridges and the guns used to fire them. Grant allowed the confederates to keep their long arms for just such purposes, to get food on the table for their families.
Sorry to have to disappoint, but your bullet definitely was manufactured after the end of the civil war. As a civil war bullet digger and dealer for over 40 years, I'll testify that your bullet does not appear in any of the reference-books on civil war bullets.
It closely resembles some modern bullets made in molds for people who like to re-load spent cartridge casings, viewable here: Ol' Buffalo Bullet Mold Tables
But I don't think any of those bullets have a flat base with a "dot" at its center. So I think that instead of a modern reporoduction, your bullet is an "original" from the 1880s, plus or minus a few years.
Thanks for the info I really appreciate it. I just measured it came out at a 1/2" so assuming it is a 50 cal. The base is concave goes down about 3/16 of an inch. Hope that helps age a little closer. I found it detecting by a river along with and old silver saddle bezel. There is nothing better then finding something in the ground that has potential. Thanks again.
Lucas, thanks for measuring the bullet's diameter. That information enabled me to identify your bullet with certainty. It is a US .50-70 Model-1871 "Government" Rifle bullet. (That rifle is sometimes called a Model-1871 Springfield Rifle). Here's a photo showing an original .50-70 bulletmold from 1880. Also, here's a diagram of the .50-70 Model-1871 "Government" Rifle, which shows your bullet in its metallic cartridge-casing.
As Gunsil indicated, when US Army rifles were superceded by a newer model, many thousands of the obsolete ones were sold to the public for big-game hunting. Then as now, a good number of hunters reload their used cartridge-casings. That is why Winchester made the .50-70 bulletmold in 1880.
Almost forgot to mention... your bullet has ben fired, even though it shows no impact damage. Your photos show rifling-marks on your bullet's sides.
I see you are a brand-new TreasureNet member... so, welcome to T-Net's "What Is It?" forum, the best place on the internet to get unknown objects CORRECTLY identified.