5.56 with 1:7 Twist & NO threads. They are Made from 4150 Chrome Moly steel and black nitrided inside and out , Gas Port is drilled. The handguard retainer slots and extractor clearance cut is already in place. These barrels are AKM Config so they will take most of the standerd AKM parts. Made By Green Mountain Rifle.
Barrel is very well made and all journals are within spec of AKM barrel dimensions. I really like how the chamber side is chamfered to aid round chambering where I had issues with another brand barrel without this feature. Highly recommended.