question on legality of ar-15 combo

[Futo Inu]

I don't know anything about these so bear with me. If I get an upper that has a 14.5" barrel with a 1 1/2" flash suppressor, for a total exceeding 16", then put it on lower that has had the stock "thumb-holed", this should be legal, should it not (no more than one offending item, in this case the flash suppressor)???

 

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FotoInu,

I don't pretend to know the various ambiguities of the federal law as interpreted and supplemented by the states and lower jusisdictions. However, to get better exposure to what is essentially a legal question, I'm going to repost this to the Legal & Political Forum.