I could be wrong.
While I have Much Imput on this thread ; I just type too Slow & tend to rant to say it all.
True Def, not a Minie Ball as it was named after it,s Designer C. Minie & as Gunsil said Conical in shape W, several types of hollow Bases.
Exact Diameter Will be needed to be sure
The Picture Does kinda look like "Pack Man" With a mouth on one side. but it could be an indention from almost anything.
Patina is hard to go by indeed but in my experience the more modern larger cal, round 'shot' does not display as much patina as period ' Shot' does & that goes for fishing sinkers as well. Maybe the lead Composition is diff, in later shot and sinkers.
Someone like The Cannon Ball Guy Wii have WAY better info than I.
IMO I'm 80% sure it's a Round Ball From CW Period ,( if not a sinker) lol
Also IMO It has the right look to it . Tho I may be wrong
Small cal, Round balls Always have been a pain for me to ID, esp if fired.
I usually go by where it was found , Diameter & the look of the Lead/ Patina.
IMO It Seems Folks went almost Strait to Shotguns For their hunting Purposes after the Civil War cause after the minie & other types of CW era Bullets I find mostly Shot Gun Brass Heads that date late1800 s - begin 1900 s . Then is 22s of all sorts Short ,long long rifle.
Est, 95% of the early Cast Lead 38,45,Cal, Bullets that I dig Don.t have much patina at all.
Good Luck Out There
Davers