SBR engraving question for build on 12" Faxon GB

[Les]

Are these barrels marked so that I don't have to have the caliber engraved on the lower? The way I'm understanding this is if the caliber isn't readily legible it needs to be on the lower. I'm planning on sending the stripped lower to Tarheel soon. I would imagine it might depend on handguard used as well.

[Bigs28]

It's my understanding that the caliber needs to be on the lower/serialized part of the rifle.

[explorecaves]

The barrel is marked. The lower, if building from a complete lower does not need to be marked as it is already marked (multi, 5.56, etc.).

And the ATF only needs notification of a permanent change to the caliber. Swapping uppers is fine all day long.