it's a Civil War era Patriotic Button.
One is shown in the book UNIFORM BUTTONS By David Johnson, 1948; Plate 86 # 1112 (Vol. 2) & Page 202 (Vol. 1 text).
Described as "V-Type A Drum on Crossed Swords imposed on multiple pointed star with a star at each point.".
Also listed in William Tice's book as # PC290AS1.
Diameter is 5/8".
They are solid brass with a steel back & eye.
One recently sold on eBay for $22.95
Nova Treasure