My experience with AR's indicates that most of the pins are not "undersize" as the result of "bad" quality. It's done that way on purpose to facilitate interchangability of parts resulting from tolerance stackup. If you get a "good" fit right out of the box consider yourself lucky. Actually, you are probably unlucky because a tight fit means something is on the extreme of one or more dimensions.
To achieve tight fitting uppers/lowers/takedown pins you usually need to purposely build it that way with oversized pins, precision bushings in the upper receiver lugs, match reaming the parts, etc. The other approach is to use bandaids such as expanding takedown pins, accuwedges, o-rings on the pivot pin lug, etc.
Most folks just live with the play between the upper & lower. It's a fact of life!