They look like they’re machined into the barrel but they are not. They are pressed into a key slot and pinned in with a cross pin. The pin is then dressed down and polished with the barrel, making it disappear.
It is very difficult to replicate and have the pin be invisible and of course blued guns will have to be reblued.
Does this also apply to the S&W Model 58? Although built on an N-frame, the barrel has the same shape as the M10 and 13 has. I think M65 frontsight may be installed the same way.
