As the 2nd Amendment states that gun ownership should not be infringed upon in order to maintain a well-regulated militia, ownership of an assault-type weapon (large capacity magazines and automatic or semi-automatic firing) should be allowed but ONLY if the buyer joins the U.S. militia: the National Guard.
As long as the owner is a member of the National Guard, they may be allowed to own one assault-type weapon. Upon withdrawal from the National Guard they forfeit the right to own an assault-type weapon. When called to active duty, the owner of the assault-type weapons must report for duty with their assault-type weapon.
This meets the requirement of the 2nd Amendment to not infringe upon gun ownership and, simultaneously, meets the prescription of maintaining a "well-regulated militia.