The VIS-1 is a hot system, and anyone looking for a "monolithic"-type setup should definitely give it serious consideration, along with the LMT MRP, which is also excellent. By the way, the “VIS” in “VIS-1” stands for two things: 1) Versatile Interface Structure, and 2) In Latin, VIS means "force" or "to use force". While we’re on the subject of Latin, Vltor (pronounced “Ooltor”) means "revenge", "avenger" or "vengeance". The "1" designation in “VIS-1” is for Vltor’s carbine series. Vltor’s mid-length series will be called VIS-2, and their rifle-length series will be designated “VIS-3”.  The process Vltor uses for bonding the two pieces of the upper receiver into one piece is salt dip brazing, which utilizes a molten salt vat.  According to Eric Kincel, salt dip brazing is a dying art form.  It creates a one-piece unit that has the same strength and rigidity as solid piece of aluminum. The mating joint (bonded surfaces) are actually stronger than the parent metal (parent material)."