I don't even see a double-barrel assault rifle being much use. A lightweight carbine with a light bolt will have a rate of fire perfectly suitable for close quarters battle or suppression, and a casket magazine immediately gives you the same capacity as a Snake. Two barrels also have a major problem: convergence. In order to achieve a semblance of accuracy, the barrels are typically slightly angled inward so the bullets converge at a specific point. Even with convergence, the gun will lack accuracy at ranges below or above that point. Without convergence, you're shooting with the sights too far to the side. A Mk 18 Mod 0 may have relatively low accuracy and range from its short barrel, but it can still hit a man 100 yards out with a single shot because the sights are aligned with the barrel.
It would literally only be useful in immediate close quarters fighting where you're relying on full auto sprays with relatively little accuracy.....and we already have regular guns that accomplish that with half the complexity and cost.
