CryoStructure HK21 7.62mm CHF 17.7" BLK Barrel

• COLD HAMMER FORGED BARREL blank sourced from a United States military supplier
• 4150 Chromoly Vanadium Steel
• Parkerized to the original German specifications to sustain FULL AUTO fire better with heat than black nitride for outer coating.
• This is the older original HK21 model
• WITHOUT ATTACHED HARDWARE 
• Fluted Chamber as in the originals
• 1 x 11 Twist Rate
• 17.7 inches long
• Thread pitch is the original German - M15  x  1
• Chrome lined
• Inspected at 100x magnification before release
• AMS 2460 process standard
• AMS-QQ-C-320 process standard
• 1.2.2 of MIL-STD-171 process standard

There is a pin located at the back of an HK21 removable barrel as a safety feature. It is there to (help) prevent the removal of the barrel with a live round in the chamber to prevent accidental discharge. The pin is offset in the chamber face of the barrel and enters a corresponding hole in the face of the bolt head. Because the pin in the barrel is offset and protrudes into the hole in the bolt face when the bolt carrier group is closed (in battery) it prevents the barrel from being rotated and then removed from the trunnion. The bolt carrier group must be opened/pulled rearward (out of battery) and preferably locked open which extracts any (live) round that may be in the chamber. With the bolt carrier group lock rearward, the barrel can rotate freely to be removed or installed in the weapon.