Your brass 1-piece "flatbuttons" are almost entirely Civilian-usage, though a few did get issued to local Militia soldiers. Also, the Confederates used a few when supplies of CS Military buttons ran low. So, three 1820s civilian flatbuttons, and no Military buttons or bullets, indicates you're at a house-site rather than a Military encampment. Two of yours have indented-lettering British backmarks, which, being dug in the US, means they most likely were imported here during the 1820s. The War-of-1812 caused Americans to boycott British-made goods for about 5 years after that war ended (1815). By the late-1820s the young American button-making industry had become capable of mass-producing enough flatbuttons to satisfy the US market, so there no longer a need to import these flatbuttons from Britain.
