FAYETTEVILLE, Ga. -- The way Jay Chambers sees it, the semiautomatic weapons in his firearm collection might be the most promising investment in his financial portfolio.

Like many gun enthusiasts, Mr. Chambers, a manager for a door wholesaler here, believes President Barack Obama and the Democrats in Congress soon will reimpose a version of an expired federal ban on the sale of so-called assault weapons. If such a law passes, he figures his collection -- enough guns, ammo magazines and weapon parts to assemble about 30 AK-47s,...