Smith M&P 9mm Accuracy and Extraction Fixed?

[Hangingrock]

This was not a problem that affected every 9mm full size Smith made. But I talked to police armorers who would get 10 guns in and six would shoot great but four of them couldn't print 6" groups at 25 yards.

This is not meant to be argumentative but rather an observation.

How could six out of ten pistols be fault free and four be problematic? This would especially be true should the ten have came from the same production run utilizing the same batch parts that the other six pistols were made with that functioned with out problem?

I would say that QC procedures with the ISO certification the the procedures and documentation would point to quality produced parts made to specification. On the other hand I've noted this observation: One may still produce junk under ISO but at least it is well documented junk.