I built mine with an 80% reciever from these guy's
http://www.ruger1022receiver.com/MAGNUM%20Page%2011.htmThe first few magazines were sketchy, they even warn that it will take a couple hundred rounds for it to function, but now the thing runs flawlessly.
The main difference between this Razor reciever/bolt and the Ruger is Select fire uses a modified charging handle and and extra spring above the bolt where Ruger uses a tungston bolt to compensate for the extra pressure of the WMR.
I got the barrel, an aluminum sleeved tensioned Volquartsen from Midway...Cheap

. The thing is a tack drivin, coyote killin, coat preserving machine.