The crusader stripped lower by spikes is a multi-caliber lower that is perfect for a custom build or replacement.It is a 7075 t6 aluminum lower that is black hard coat anodized for superior protection against wear and tear and the elements.Spikes is a very well respected manufacturer of parts and firearms.Type: Lower ReceiverGun Model: AR-15Gun Type: AR PlatformCaliber: Multi-CaliberMaterial: 7075 AluminumFinish: Black Hardcoat AnodizedTrigger: None