6.20mm Delta Strike Barrel 300mmDescription The Prometheus 6. 20mm Delta Strike Widebore inner barrel provides great stability to BBs with its 3 point retention insert and extended hopup window. The 3 point retention insert centers the BB to the middle of the bore, while the extended hopup window provides even great backspin, effectively increasing range. The 6. 20mm wide inner bore allows for air to cushion underneath the BB as it rides along the top, in effect preventing the BB