BSF Barrels Blank .338 Bolt Action Threaded AR Barrel 5/8x24 1-8 24in .930 Strait Black/Stainless. they use this jacketing method rather than wrapping the barrel in carbon fiber because this method of wrapping has been proven to trap heat and cause delamination. The carbon fiber they use is specially designed to move at the same expansion rate as 416R stainless steel. If you choose to have the carbon ported they machine slots into the carbon fiber allowing air to move around the barrel and vent heat quicker without any delamination issues. Using the Carbon Fiber this way keeps the rifling straighter the warmer the barrel gets because it's under tension. This allows they to maintain superior stiffness and strength while keeping the barrel extremely lightweight. Package Contents: BSF Barrels Blank .338 Bolt Action Threaded AR Barrel BSF Barrels SF3IYT2351: Blank .338 Bolt Action Threaded AR Barrel 5/8x24 1-8 24in .930 Strait Black/Stainless