If NICS was compelled to reply to EVERY gun transaction in the U.S., it would crash, and they know it.
Surely merely a question of adding computing space, and if denials/whatever required a human in the process at some point, Obama wouldn't care if that process stretched out for months.
And most private transactions are INTRASTATE, which brings up the whole issue of "federalism" if the feds try to regulate them.
Most private transactions are that way in part because interstate private sale/transfers are illegal. Law-abiding folks usually obey laws.
But in this case, since the Feds already regulate commercial interstate AND intrastate sales involving FFL dealers via background checks etc, passing a ban on undocumented private sales would merely make private sales subject to the exact same regulations already in effect for commercial sales.
Birdwatcher
