I take my pocket knife and with the blade perpendicular to the mold lime I drag it across scrapping it flush. If you don’t press too hard and don’t rock back and forth you don’t get any further unslightliness and it feels better. It’s the sort of thing I generally do sitting in the deer blind etc bored.
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I'd usually whip out my pocket knife, and then wonder why the blade gets dull so fast when trimming parts with 40% glass fill
When building samples that had to look perfect, the toolshop guys would do something like trim the flash and then gently bead-blast the part with a grit similar to the mold interior. I'm not that skilled.