tobnpr, it's according to the CNC setup, the machines precision, tooling, and operation. There are some new machining centers, that have a rotary indexed work holding collet or chuck, so one can machine the receiver's front and rear in the same machine and setup, without removing the receiver. Those are pretty accurate, but any heat treating can still warp it, even though they use special jigs and methods to control it. A good example of a modern CNC machining center, for this, would be like a lathe, which had an indexed rotary chuck that holds the receiver, which can swing the receiver a precise 180 degrees to the tooling, thus doing both ends in one go.
Several of these older gun factories still use many of the older machining methods, since the factory is set up around that and certain models, where they use pretty much the same fixtures and jigs. They are modernizing, but I have noticed that some still use older tooling. Of course, in blueprinting, we're talking about the difference between creating a fine match rifle, and a hunting rifle, that is made as cheaply as possible.
Another problem is the quality of the barrels manufacture, and if they profile the OD, and turn the shank, concentric to the bore. That is why blueprinting generally uses oversize threads, to correct any misalignment, along with boring and re-threading an offset receiver thread.
If you get a chance, watch the Remington Ilion factory video on YouTube. They still use some of that older specialty equipment and methods, or did the last that I know of. Some of those machines were designed and built just for Remington.