IIRC, the US Constitution applies to its citizens. If a non-citizens wishes to purchase and has to answer a question, there is no inherent violation of the 2nd Amendment.
All Men may be created equal, but the 2A to me is only for Citizens.
Many Constitutional rights apply to citizens and non-citizens alike, for the simple reason that the Constitution (and specifically the bill of rights) does not create or grant rights, but simply protects those rights from intrusion by the government.
It may be the case that the Constitution does not protect certain rights (perhaps even the Second Amendment rights) of non-citizens, but it is not accurate to flatly state that Constitutional rights do not apply to non-citizens.