These are all melonite coated inside and out. Melonite is stronger and more effective than chrome lining because it does not pit. All are chambered and marked for 300AAC with a 1x7 twist. Threaded to 5/8x24

All are chambered and marked for 300AAC with a 1x7 twist. Threaded to 5/8x24 10.5"
They include the barrel extension with M4 feed ramps. Made by Mossberg