This
You can swap upper configurations at will.
and this
It only becomes illegal if it is possessed/attached to a postban AR lower.
contradict each other.
The first one reads as if the AR15 owner may use any configuration he wishes on
any given lower. I know that isn't strictly what you meant. But I think you can see where the confusion arose when the necessary caveat of mating it to the appropriate lower was omitted. I believe you meant to say that any upper configuration could be mated to a pre-ban lower. (I also understand that only the lowers are categorized as pre-ban by date; but by default any upper can just as easily be categorized as pre-ban or post-ban based on its features and the lower to which it can be attached; I think (hope) most AR owners understand the subtle difference.)
I also understand how my statement of
don't alter the pre-ban barrel. Once you do you can never really go back (meaning you can make a pre-ban a post-ban, but not vice versa.)
is not entirely correct, by definition. I can see how one might read it to mean that lowers can never legally have the evil features reattached, which of course they can. Regarding the bayo lug/front sight block: once it's shaved, it can never be "unshaved" to return it to the pre-ban configuration full of "evil" features. I realize he can legally return it to pre-ban config by removing the old shaved front sight block and installing a new front sight block with the bayo lug, but
that particular front sight block can never be returned to its original configuration. That was the basis of my comment.
And to muddy the waters even more (though please understand I'm not trying to pick a fight by any means):
It is the preban lower that can lose it's preban status, not the upper.
By your own admission, the lower is the only thing that is accurately labeled pre-ban since it is categorized by date of manufacture (assuming part of a complete rifle, that part is important). If that is the case, then how is the above statement true?
And finally:
As long as he is not taking a complete preban AR and using that upper to build a post-ban AR, he's OK.
Again, not entirely true, as you've said before. It would only be a problem if he failed to remove the requisite number of evil features. He's still legally allowed to take the upper from a complete pre-ban rifle and mate it to a post-ban rifle
assuming the evil features had been removed, right?
I know it seems like I'm nitpicking and maybe I am a little bit. But this stuff is serious business and people can easily and innocently make a mistake that hurts them bigtime. I think it's imperative that all the details and assumptions and caveats are stated when making affirmations about the legality of configurations and lowers and whatnot. I just feel that these were left out sometimes (which apparently led to the confusion).
I think we both know what we want to say, but neither one of us were crystal clear. Hope I didn't ruffle the feathers any.