The semi-automatic rifle has been in wide circulation for more than a half-century. In recent years, gunmen have used AR-15-style weapons to carry out many of the country's worst mass shootings.

The AR-15 is more than a weapon. It’s also a symbol. This investigation sought to understand the rifle’s impact, and here’s what The Post learned.

The AR-15's shell is designed to blast out its relatively small, heavy slug at an extremely high velocity, making it too dangerous for civilian use.