Just an update for everyone, we tested out some steel core surplus 7.62x39mm with the rifle using a cheap barrel. As expected, the cases stuck and extraction was hard. Extraction is hard with this ammo in my Cz527 also. We are waiting on some S&B ammo to test next. We are also going to get a better Faxon barrel.
We also did some long range shooting last weekend. Making hits out to 500m with 55 grain American Eagle 223 was easy peasy. This ammo is hotter than other stuff we have played with and extraction was no issue with the Faxon barrel. I personally look forward to trying out a PRS match or two with this rifle. For these types of matches you often need to start with the bolt back, so good thing there's no spring in there. Also easier to show clear.
The build we did with M&P 15 donor parts works great. All ammo worked well with zero extraction issues. Extraction is very very smooth.
We are getting pretty high round counts on a couple guns now. We have seen no issues with wear, receiver warping, metal fatigue. While there is no gas going into the bolt, cleaning the bolt is still required occasionally. Running a bore snake thought the barrel is the easiest way to clean the rifle. Just push the bolt to the rear and feed the snake thought. If you want to remove the bolt it's was easy as removing a screw.