Back in 1968 there was a proposal (by Colt, apparently) to shot peen both upper and lower receivers to "provide a more durable finish and to aid in the prevention of
exfoliation and inter-granular corrosion". It seems this was never approved by the Army, but looking at it in 2017 would this make sense or is it just something that was impractical/theoretical?
http://www.dtic.mil/get-tr-doc/pdf?AD=ADA953121
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