Every rifle is “piecemeal”— that’s the whole point of interchangeable parts. Otherwise we’d all be dealing with the hand-fit process that 1911 lovers consider art and some us consider obsolete.

I work with parts where tolerances are held to under plus/minus 5 microns. A human hair is typically 100-150 microns thick.

With modern CNC machining centers, holding under a thousandth in most dimensions is cake. Tolerances stacking will not cause fitment issues or function issues.

Think about it this way. In any assembly made of parts there are only three kinds of defects: either the part is improperly designed, part is improperly made, or it’s improperly assembled.

Buying reputable mil spec parts all but rules out bad design or manufacture, leaving only assembly.

In this case, we know assembly is pretty simple and not likely wrong, which leaves only a part that is poorly made or designed.