Of course the Feds can regulate gun ownership. Commerce clause. End of story.Of the enumerated powers the federal govt is granted, not one of them is regulating firearms. The bill of rights was a mistake as many at the time thought, as enumerating rights is somewhat saying govt grants rights, and that is not the case. The constitution limits govt by saying what the federal govt CAN do, not what it specifically can't, which is why the bill of rights is a mistake, redundant and has allowed for this sabotage over the years. But the 9th amendment clarifies the original intent.
But are states allowed to regulate a right?
The 14th through the due process clause fully incorporates the bill of rights against the states, including the 2nd. Please read http://www.law.cornell.edu/supct/html/08-1521.ZC1.html for a better explanation than I can give.