The problems I've seen personally were with the 556R, not the 556.
The problem with the 556R wasn't that Sig was trying to make a precision rifle, it was that Sig put a poorly designed rifle with glaring quality control issues on the market.
The original had steel mags locking into aluminum which only took a few hundred rounds to start to cause serious erosion. The head spacing was way off on many examples, mine included. It was so far off that rounds wouldn't seat under the extractor and would fall off the bolt face when the bolt/carrier was retracted. The fit and finish was nothing shy of atrocious. The plastic furniture was cheap and easily broken with normal use (mine broke almost immediately). The barrels weren't chrome lined or nitrited.
Sig seems to have corrected most of these issues but haven't marked the second gen rifles any differently than the first gen rifles with all of the problems. I still see brand new first gen rifles on shelves of stores. You better know what you're looking for if you buy one or you will wind up with a rifle that should in all honesty be recalled.
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