Franklin Armory 00-20016-BLK: This binary trigger equipped Franklin Armory lower is the perfect foundation for any rifle build. The forged 7075 T6 aluminum lower provides more than enough strength to handle the binary trigger\'s faster rate of fire. This lower would be a great starting point for a military M4-inspired carbine since it already comes with a Mil-Spec 30-round steel magazine, a familiar A2 pistol grip, and a classic M4 carbine stock. The finish is the tried and true Type-III Hard Coat Black Anodized finish, which is excellent for corrosion and wear resistance. Franklin Armory thought of everything and built this lower receiver with a specialized tension screw. This feature eliminates the dreaded wobble between the upper and lower receiver. So no matter which upper receiver you decide to go with, you will have the perfect fit. While all these features make this lower great, the ultimate highlight has to be the BFSIII Binary Trigger pre-installed and tested at the factory! Please see extended description for complete details on the BFSIII Binary Trigger.