A fully automatic M16 rifle that went for $800 in the 1980s before it came under stricter federal control now goes for $25,000, a 30-fold increase and more than it would be worth if made of pure silver. And, thanks to the laws of supply and demand, the going price is still climbing.A storied weapon carried by U.S. troops, the M16 is a case study for potential investors as President Barack Obama and gun control advocates press for sweeping changes in gun laws.The frenzied run on guns and ammunition occurring at gun dealers across the country after the mass murder at Sandy Hook Elementary School in Newtown, Conn., was predictable. It happens every time the nation's attention focuses on the divisive issue of gun control.Much of the weaponry is being snatched up in part out of concern that it might not be available at stores later, in the event of another assault-rifle ban -- a previous such prohibition expired under President George W. Bush -- and restrictions on high-capacity magazines.Others see these times as an chance for a shrewd investment by stockpiling weapons, magazines and ammunition hoping to sell them later for a profit.Houston-based political consultant Allen Blakemore, for example, said he dipped into his children's college fund and jumped into weapons-investment for the first time by buying 200 new high-capacity ammunition magazines."At this point, it is economics," he said. "I certainly don't need that many. It becomes an opportunity to buy something at one price and sell it at a higher price."Blakemore said that 90 days ago, the magazines were selling for $15 a piece; they now go for $75.Obama called for a ban on assault rifles following the December massacre of 20 Sandy Hook kindergartners and six staff members. That shooting followed an attack in an Aurora, Colo., movie theater in July 2012 where a dozen people were killed and 58 wounded."The type of assault rifle used in Aurora, for example, when paired with high-capacity magazines, has one purpose -- to pump out as many bullets as possible, as quickly as possible," Obama said in a speech to the nation after the Sandy Hook shooting.A generation earlier, prices for fully automatic weapons like the M16 started to climbed thanks in part to a law signed by then President Ronald Reagan that said they could no longer be manufactured for civilian ownership.Making an investmentHouston attorney Al Van Huff said he has already invested in a stash of M4 carbines that he plans to keep in mint condition. Van Huff wouldn't say how many he bought or how much he paid for the guns, other than that he paid "market price" at the time."I bought several because they are not going to go down in value," he said. "... If an assault-weapons ban were passed, they would at least double in value right away."Weaponry, including guns, ammunition and components, is selling so fast it isn't even sitting on shelves at some stores.Jerry McCall, owner of gun stores in San Antonio and Kerrville, said he has been in business 20 years and never seen anything like the ongoing blitz."I can't get handguns. I can't get long guns. I can't get anything; everything has been bought up," he said. "I can't get ammo."