from my understanding it is 10x stronger than steel
Scientists have yet to figure out a way to mass produce sheets of graphene in large sizes, thus, for this experiment, the researchers confined their efforts to a very small scale. Their firing range consisted of using a laser to vaporize gold filaments to serve as the gunpowder. The explosion pushed micron-sized glass bullets at graphene targets—10 to 100 sheets placed together to form a mat—at speeds up to 6,700 mph (approximately a third of the speed of a real bullet fired from an M16 machine gun). Electron microscopy was used to measure how well the graphene sheets absorbed the impact.

Read more at: https://phys.org/news/2014-11-graphene-bullet.html#jCp