Yes
Some of these may date to the 1500s. The double barreled gun was simply two regular barrels, joined by solder. A later form from Germany in the 1800s consisted of 2 shotgun barrels plus a rifle barrel- known as drillings, from the German word for 3.
No, according to RCW 9.41.190: "It is unlawful for any person to manufacture, own, buy, sell, loan, furnish, transport, or have in possession or under control, any machine gun, short-barreled shotgun, or short-barreled rifle; or any part designed and intended solely and exclusively for use in a machine gun, short-barreled shotgun, or short-barreled rifle, or in converting a weapon into a machine gun, short-barreled shotgun, or short-barreled rifle; or to assemble or repair any machine gun, short-barreled shotgun, or short-barreled rifle." You can thank the assault weapons ban for this. There are exceptions though: http://apps.leg.wa.gov/RCW/default.aspx?cite=9.41.190
Double barreled shotguns are manufactured in several countries.
Yes.
Gun shop, gun show, Shotgun News, Gun List
30-40 years.
No, but, the Blue Book of Gun Values might.
Double Barreled Shot Gun Double Tap Iron Lungs Worst :D
Yes. It is not a short barreled rifle, but is a handgun. Legally. Yes, I know what it looks like, but it is classed as a handgun.
Depends on the gun- the mass of the barrel, the size of the cartridge, and how rapidly it is fired. A heavy barreled .22 target rifle will barely become warm to the touch- a light barreled .308 sporter will become hot enough to burn your hand after 5 rapid shots, and a belt fed machine gun can turn a barrel red hot.
Long barreled gun, with grooves on the inside of barrel- is a rifle. Shorter version is a carbine. Handguns, such as pistols and revolvers also have grooved barrels.
10 gauge. Most likely black powder.