The problem is that you need 20 different sized screw drivers in different widths and thicknesses to suit what ever odd ball size slot the manufacturer decided to make. My dads JW15 has 3 screws all with different sized slots that hold the trigger guard on. I'd much rather need a single torx or allen driver than need 3 flat head screw drivers.
Usually the problem comes when someone doesn't have the correct sized screw driver, so "makes do" and buggers them up.
Non firearm related but old flat head wood screws are shit house as a flat head bit in a cordless drill doesn't like to stay in the slot, especially after years of people" making do" with what screw driver they had.
When several better options exist there is no good reason to keep using them.
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