We bought 3 receivers (one for me) to build 338NM. I chambered all 3 barrels. Our FFL guy sent the receivers to be Nitrided, barrels fluted, then Nitrided.
Melonited receivers ran smoothly.
The FFL guy finished his rifle with AI chassis, zeroed it with this group launching 300 grains SMK. Then, proceeded to run all the way to 1200 on steel eSilhouette. Confirmation on targets showed 1/2 MOA through 900. MOA the rest. Waterline maintained, wind did the damage.
With over 200 rounds now through the rifle, the action ran smoothly, no hiccups.
Edit: I chambered my barrel first. With the tenon and headspace dimensions from my barrel. I used my numbers to chamber the other two
When they brought their receivers, their barrels screwed right up, headspace go/no go checked out. Bottom line, the receivers are fairly close in their critical dimensions.
Maybe we just lucked out.
Whoever chambers the barrel they need to accommodate the M16 extractor clearance as it rides over the rim during chambering. People who chamber barrels already know this. Just throwing it out there.