Stef45, sorry to disappoint, but my area of "deep" bullet-knowledge is the civil war era, with "some" additional knowledge of 1866-1890s US military bullets. Here's all I can tell you:
Your bullet is not a civil war bullet and not a military one. I agree with NOLA_Ken and Tony that it appears to be a .32-caliber, for pistol. In some of the photos it looks like it has some white "pure-lead" patina under the dirt, and if that is correct, I think its more likely to be from the late-1800s/early-1900s.