It’s called the Quattro-15 and it’s a fat magazine well AR-15 lower receiver designed to accept Desert Tech’s new Quadmag-53, a quad-stack, 53-round magazine. It works with any standard AR-15 upper.
Desert Tech told me that they designed this magazine from the ground up to function reliably in a quad-stack format, which is why it doesn’t taper down to double-stack in order to fit into an existing AR-15 magazine well. They say when they threw that restriction out and decided to accommodate the lower to the magazine instead of the other way around, they were able to achieve reliability that meets military requirements.
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