Caliber: Multi (will accept any lower and/or caliber designed for the AR-15 platform)
 
Other Specifications and Features of the G-15 Forged AR-15 Upper Receiver:
Machined from 7075 T6 aircraft grade aluminum forgings (Forging Marks May Vary on Availability)
Matte black hard-coat anodized per Mil 8625 Type 3 Class 2
M4 Feedramps
Compatible with all standard AR-15 components and most aftermarket parts
Manufactured to MILSPEC on state of the art CNC equipment for consistent quality parts and exacting tolerances
Save money by building your own AR-15 rifle from the ground up exactly the way you want it configured
Designed to match lines with New Frontier Armory G-15 Forged Lower. C-4 Billet Lower, and most other standard AR-15 Lowers