YHM originally designed a Billet lower that mimicked a standard (forged) lower receiver, but after seeing the prototype production they decided to go with a receiver that was more stylized, something that didn't look like every other AR-15 on the planet. It was this mindset that helped YHM arrive at the Model-57, and in turn this lower receiver. This lower is crafted from 7075-T6 aluminum and has a hardcoat anodized matte black finish. It features an oversized magazine well chamber for easier magazine changes. It accepts all generations of PMAGs and Mil-Spec upper receivers. It has a built-in, oversized, machined trigger guard. It fits all standard parts (except for a trigger guard) and still fits, and functions with your standard upper receivers.