So far as I know,
Blind pinned, but the pin cant be removed, if it can it doesn't count, welding the pin ensures this.
High temp silver solder.
So far as I know,You don't even have to weld over the pins!
Doesn't require an FFL. Just work on the barrel separate from the firearm, make sure it's a 16"+ barrel when you put it back in the rifle.That's the reason for other approved methods(dissimilar metals), either way I believe it has to preformed by a FFL.
If the barrel stayed attached to the firearm, one would be manufacturing a SBR, that would require an 07FFL and SOT, and maybe technically, paper work, or a letter from the ATF.I will not dispute on that, because I don't represent the ATF. But a few years ago, one of the local smiths tried his version of "linear" pinning vs radial pinning, he won his case but it was questioned!