Suwannee Tim --
I appreciate your response. My intension is not to cut corners but to build a safe and reliable upper. I have a second upper in the works that will use a F-stamped FSB on a M4 carbine bbl purchased from BCM. I just got a look at the parts today and the only predrilled holes I saw in the FSB were for the gas tube (as expected). The tapered pin holes are absent but that's a project for another day. I don't know the tensile strength of those roll pins but I'm pretty sure the pin plus two set screws should hold the GB very securely. Again, not trying to cut corners. I order from McMaster all the time and may go for a grooved pin if the roll pin doesn't work out. But that's why I'm here asking questionsThanks again for your suggestion.
-- ale


Thanks again for your suggestion.
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