Bolt fit
This just hasn't been my experience. Older production receivers required more fitting, but I found that they could usually be adjusted with minor honing to the bolt lugs. Over the years, I have only had to return two receivers for being too far out of spec. One was a machining omission to the rear sight windage detents (that one really fell through the cracks) and one that the left recoil lug shoulder had an excessive gap that couldn't be corrected without excessive alteration to the right bolt lug.
I should note that I have returned many more receivers of other manufacturers. Entreprise and Armscorp being the most out of spec. I have also sent back an occasional Springfield receiver, but M1A receivers are generally very good and consistant for cast receivers.
I haven't found any manufacturer has produced perfect receivers throughout there production history. What I found with LRB is that they have made continuous improvements throughout their production and were able to make corrections very fast when they turned up. This probably has a lot to due with the fact that they are a small manufacturer and produce receivers in small lots so the problems that they have had only effected a few receivers and were corrected promptly. LRB is noted as being very responsive to input from armorers who build on their receivers and many of the improvements have been due to this direct input. I know of no other company making M14 receivers that has been so responsive to their customers.