The Firebolt is a printable AR-15 lower that, unlike other printable lowers, is built using several individual printed parts which bolt together. In this way the lower is highly modular - the lower can be adapted for use with many different calibers simply by swapping out a few pieces. Supported calibers include .223 (AR-15), 9mm (AR-9) and .45 (AR-45). Furthermore, any individual piece that wears out or fails can be reprinted without having to reprint the entire lower. The Firebolt has several different options for the buffer tower. A standard buffer tower is included, but options are also present that allow the use of a reinforcing U-bolt, as well as a printable buffer tube. The Firebolt excels in strength, modularity, and efficiency and is one of the most popular AR-15 lowers available today.