Receivers are usually not an issue, until that rare occasion when they are. The bedding, barrel, mounts and other usual suspects have been tested on this rifle. Maybe its time to consider that the receiver may be a little flaky. I don't mean out of spec but that it may have issues that show up only under the stress of firing.
It's been a few years back but a poster on here mentioned he had a NULA that wouldn't shoot. After some back and forth it was discovered that the heat treat on the receiver was not to spec (too soft) and that was causing accuracy problems.(NULA starts with heat treated stock to mfg. the receiver. They received some bad stock as I remember the story.) New receiver=problem solved.
The British SMLE was capable of very good accuracy but has that flexible receiver. The way I remember reading that story, the armorers for the shooting teams would start by picking known accurate rifles to rebarrel. Putting a match barrel on a known shooter worked well but putting a good barrel on a random receiver was a crapshoot.
