It's a logo of a pointed bullet still in it's casing. The casing is much larger than the bullet as is common in a high powered rifle. The rectangular shaped casing has a little glint of light on it making it look like it is shiny.
This Ammo icon is made in Material Design style
developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 5,700 icons, all in the same style and quality.