Clint Smith is the chief instructor of thunder Ranch shooting school. I spoke to him about 20 years ago when I was thinking of taking his class. He has a channel on YouTube. He's pretty wacky, and probably halfway off his rocker, but he's entertaining, and old school, and it sounds to me like he knows what he's talking about. His YouTube channel is "thunder ranch".
In one of his videos, I think he says that the original forward assist on an M-16 was a little divot milled into the right side of the bolt that you could use to push the bolt forward with your thumb.
I'm not an M-16 guy, but I had never heard that before.
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