Yeah they mill the flashing after. They just went overboard to hide the mistake on the cheek.
But yeah, they probably have some people running a swivel/deburring tool up and down, gouging the shit out of everwhere else.
Hell here is Phagan using a file on the magwell.
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A top-tier mold design has ZERO flashing. The last company I worked at wouldn't have allowed ANY flashing on a part. It was straight to packaging or annealing from the mold. There was millions of dollars into the engineering of that mold that YOU were running the mold wrong if you were getting flashing.
At least not until the mold ran hundreds of thousands of times and wore down...