STANAG magazine
For fundamentally the same reasons that a .277 inch (7.04 mm) diameter bullet was selected for the 6.8mm Remington SPC (i.e., ideal mass-to-diameter-to-length for mid-weight bullets constrained to loading in an AR-15/M16 STANAG magazine), 6.8mm became the caliber for a new AR-15 wildcat. Like the .300 AAC Blackout and unlike the 6.8 SPC and other "larger bore" AR-15 cartridges, the .277 Wolverine is based on the widely available 5.56×45mm parent case. Therefore, rifle components such as the bolt and magazine are interchangeable between 5.56×45mm and .277 Wolverine firearms, and standard AR-15 magazines can be used with no loss of capacity. A new barrel is the minimum required component to convert a standard AR-15 to .277 Wolverine.