June 20, 2013May 11, 2013 Installation of a Rainier Arms Select Barrel and gas system on a Mega Arms MATEN upper receiver. Share this gun video:Click to share on Facebook (Opens in new window)Click to share on Twitter (Opens in new window)Click to share on Pinterest (Opens in new window)Click to share on LinkedIn (Opens in new window)Click to share on Tumblr (Opens in new window)