I just completed a AR accurizing course and one of the (main) things that we did was truing the receiver face, shimming the barrel if needed and bedding the barrel using green loctite.
In my case the groups went from 1.3 and 1.47 MOA at 100 yds
to .53 and .88 MOA.
Roughly cut my groups in half.
Not bad for a chrome lined barrel and less than $5 in extra materiel.
That is if you are actually interested in accuracy.
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