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Hi Vincent, it's 1:9 twist M4 barrel. Specifications and Features: CORE15 Mil-Spec Forged 7075-T6 Lower Receiver, Type III Class II Hard-coat anodized finish Beveled Magwell for improved reloading speed, machined chevrons in front strap, bullet pictogram safety markings CORE15 Mil-Spec Forged 7075-T6 M-4 Upper Receiver, Type III Class II Hard-coat anodized finish M4 Feed Ramps, (1913 Picatinny rail flat top) with dry lube internal finish and laser engraved T-markings 16" 4150 CMV Chrome Moly M4 Profile Chrome Lined Barrel 5.56 NATO caliber (accepts .223 Remington) Direct Gas Impingement Gas System Gas Tube made of 304 grade Stainless Steel Chrome lined 8620 Stainless Steel Bolt Carrier and Bolt Carrier Key Magnetic Particle Inspected (MPI) Carpenter 158 Bolt Assembly A-2 Flash Hider "F" Marked A Frame Front Sight Base (Forged) M4 Style Thermoset molded Polymer Hand Guards with Dual Heat Shields A-2 Pistol Grip CORE15 Six Position Retractable Stock CORE15 Hardcore Billet Charging Handle

Its a 1:7 from the core website CORE15 16 Government Profile 1:7 Twist, 4150 CRMOV Black Nitride Finish PART NUMBER 100278 WEIGHT 5.9 lbs. (2.68 kg) Unloaded CALIBER Chambered in .223/5.56 x 45 mm NATO UPPER RECEIVER CORE15 Mil-Spec Forged 7075-T6 M-4 Upper Receiver, Type III Class II Hardcoat anodized finish, M4 Feed Ramps, (1913 Picatinny rail flat top) with dry lube internal finish and laser engraved T-markings LOWER RECEIVER CORE15 Mil-Spec Forged 7075- T6 Lower Receiver, Type III Class II Hard-coat anodized finish, beveled Magwell for improved reloading speed, machined chevrons in front of magazine well, bullet pictogram safety markings BOLT CARRIER CORE15 Mil-Spec Carpenter 158 Steel Bolt, M16 Chrome Lined 8620 Steel Carrier, Mil-Spec Staked Gas Key, Tool Steel Extractor, Shot Peened CHARGING HANDLE CORE15 HARDCORE V.1 BUFFER TUBE CORE15 Standard Mil-Spec GAS TUBE 304 Grade Stainless Steel BARREL *******************CORE15 16 Government Profile 1:7 Twist, 4150 CRMOV Black Nitri

Core used to do a 1:9 Twist on their rifles. They went to the 1:7 twist a few years ago and this UPC code is of recent manufacture. So the barrel will be stamped 1:7

Go to Core's website. https://core15rifles.com/core15-m4-piston-rifle-clone.html

Its a 1:7 from the core website CORE15 16 Government Profile 1:7 Twist, 4150 CRMOV Black Nitride Finish PART NUMBER 100278 WEIGHT 5.9 lbs. (2.68 kg) Unloaded CALIBER Chambered in .223/5.56 x 45 mm NATO UPPER RECEIVER CORE15 Mil-Spec Forged 7075-T6 M-4 Upper Receiver, Type III Class II Hardcoat anodized finish, M4 Feed Ramps, (1913 Picatinny rail flat top) with dry lube internal finish and laser engraved T-markings LOWER RECEIVER CORE15 Mil-Spec Forged 7075- T6 Lower Receiver, Type III Class II Hard-coat anodized finish, beveled Magwell for improved reloading speed, machined chevrons in front of magazine well, bullet pictogram safety markings BOLT CARRIER CORE15 Mil-Spec Carpenter 158 Steel Bolt, M16 Chrome Lined 8620 Steel Carrier, Mil-Spec Staked Gas Key, Tool Steel Extractor, Shot Peened CHARGING HANDLE CORE15 HARDCORE V.1 BUFFER TUBE CORE15 Standard Mil-Spec GAS TUBE 304 Grade Stainless Steel BARREL *******************CORE15 16 Government Profile 1:7 Twist, 4150 CRMOV Black Nitride