These are used to reroll the stats on your weapon. Think of it like a dice roll where anything is possible. Consumed by right clicking on your gun and selecting [Reroll Stats] under the upgrade menu.
It is important to keep in mind that using these, it does not guarantee an upgrade of the weapon.
The recommended way to use them, if you've already got a gun with good stats, is to have a "secondary" weapon you reroll until it is better than your current one.
The best roll is a supreme which gives stat 10 on everything, rolling supreme is a 1/500 chance!
During the “ROLEY POLEY” Event, your odds on making a weapon supreme increase so watch those events!