you and your bump firing... lol ak or any assault rifle is not illegal in the United States. There are some exceptions, Commfornia and a few major cities. You can buy any assault rifle so long as its semi-automatic and keep it locked up in a hard case when its not in use.
the only ak-47s that are now illegal are the ones that are completely constructed overseas. The BATF decided that a certain percentage of the parts in the AK-47 must now be made in the USA.

theyre all legal to own... for now anyway.