I've owned a WE SCAR and an M4, ran both stock at first and in one session on the M4 put close to 1,000 rounds through it, not one single failure of any kind. Threw in the RA Tech NPAS and still had zero problems. This was on a brand new V.3 straight out of the box.
Never seen the KJW, but don't discount WE guns either. In my experience, they're tanks.
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