The old saying goes "one is none and two is one." I think that was original supposed to refer to Twix bars or perhaps something to do with the amount of pocket watches carried by your grandfather. Now days preppers use this one sentence argument to convince their wives they need more gear. Either way having a double rifle is more than just awesome, it is American...
Before you set down your Natty Ice and pick up your credit card, you need to know this beast is for law enforcement only. Sorry folks, but maybe someday SlideFire will make a stock for a semi auto version of this rifle. The above mentioned rifle is called the Siamese M16 and is made by Tromix. The gas tubes are crossed and work with each other for that high rate of fire.
Although this looks ripe for a cameo in walking dead, I doubt it is at all practical. I'm not exactly sure how you can reload in less than five minutes and you can bet there is no tacticool "sleight of hand" fast reloads on that top rifle. I feel like aiming might be a bit of a problem with that mag in your face. Lastly, I can only imagine this thing has to weight 20+ lbs. fully loaded.
You can visit the official Tromix site if you want, but it hasn't been updated in a long time and their internal link to this rifle is totally busted.