(1) It is against the law to sell a stripped receiver to anyone under 21 years of age-
(2) Would it in any way be possible to sell the lower as a "rifle" if included with a rifle kit? I mean, the guy is buying a rifle...
(3) Does it matter if it is in pieces?
(1) It is aganist Federal law for a FFL dealer to transfer a stripped reciever to a person under 21 years of age.
(2) The only way it would be possible to sell the lower as a "rifle" with a rifle kit, is when the kit has beed used to build the lower into a rifle. Which would require you to be licensed as a manufacturer.
(3) Yes, it matters that the parts are in pieces, because as long as the receiver has never had a shoulder stock and a 16" or greater rifled barrel attached to it, it can still be legally made into a handgun.
A FFL dealer can only transfer a "rifle" or a "shotgun" a person between the age of 18-20.
A stripped AR lower is transfered as an "other", therefore it can not be transfered to a person under 21 years old by a FFL dealer.
A complete AR lower with shoulder stock does not meet the definition of a "rifle" or a "shotgun", therefore it can not be transfered to a person under 21 years old by a FFL dealer and is transfered as an "other".
In order to meet the definition of a "rifle", the complete AR lower with shoulder must also include a 16" or greater rifled barrel.
In order to meet the definition of a "shotgun", the complete AR lower with shoulder stock must also include a 18" or greater smoothbore barrel.
Here is a BATFE letter stating that a complete AR lower with shoulder stock attached is not considered a "rifle". Therefore, as long as it never had a 16" or greater rifled barrel attached to it, it can legally have the shoulder stock removed and made into a "handgun". Since, the complete AR lower with shoulder stock attached is not considered a "rifle", it must be transfered as an "other".