Yes this comes with the BCG: **The Maxim PDX U.R.G ships with your choice of a Standard Mil-Spec BCG to be used with most common M4 compatible lowers, or a PDX/SCW compatible BCG buffer and Spring.
The milspec version is here: https://www.opticsplanet.com/maxim-defense-industries-mdx-505-mil-spec-urg-upper-receiver.html