The 6.5 Grendel is chambered with a semi-auto match-type chamber. These barrels are threaded for and furnished with a pinned barrel extension with proper headspace and the gas port hole drilled and an 11º target crown in a match grade barrel. We are milling a narrow flat on the bottom side of the gas port section for set screws used with some types of gas blocks. This prevents marring of the .750″ or .936″ diameter by the set screws and helps align the gas block with the gas port hole. All current production drop-in barrels use an M4 style barrel extension. The front section of the barrel is engraved with “Lilja 6.5 Grendel 8T”. Just add your gas block and tube and drop into your upper receiver. This image shows the three AR-type contours that we are keeping in-stock as a drop-in type barrel (muzzle threading is standard but not shown in image). The top contour is our AR24 contour, the middle one is our AR740 with the Wasp weight reduction section turned on the .975″ diameter. The bottom contour is the carbine length gas system M-4.