What era is this bullet from?

[Jayson's Treasure Hunting]

I found this bullet in a farm field in Missouri about 5 miles east of the Missouri River in Platte County, was wondering if anyone knew about how old it might be. It has two rings, the bottom is slightly cupped, it is about 5/8 inches long and 3/8 inches wide. Thanks.

 

[MangoAve]

Sometime after the civil war. I got a two ringer myself from NE but mine's just a bit larger than a .22. The three ring ones started being used during civil war time.

 

[Full Metal Digger]

It's kind of small but it looks like a Civil War-era Gardner bullet. Perhaps a pistol round?