First... welcome to TreasureNet's What-Is-It? forum.
Your button's construction is 1-piece solid cast "white metal" alloy (called "white" to distinguish it from iron and yellow, orange, and pink/red metals). Your button's solid-cast body resembles some 200-year-old buttons, but the small raised circle next to the pillar-shank on its back indicates it was manufactred in the modern era. A similar button was discussed in this forum about a week ago.
http://www.treasurenet.com/forums/what/353550-lil-help-button.html
That being said... it's always helpful for a digger to include information about where (town and state) the button (or other object) was dug, because that can be important for accurately time-dating it. For example, if a 1-piece solid-cast button was dug in Arizona, it almost certainly is not the 200-year-old kind.