About the BCMA(R) KD4 Spec Complete Upper Receiver w/ QRF-12 Handguard KD4 Upper Group with twist rate designed for 77 grain Black Hills ammunition. Upper Group features: BCMA(R) SS410 16" Mid Length Upper Receiver Group w/ BCMA(R) QRF-12 Handguard, 1/7.7 Twist DLC Finish on barrel. DLC Coating stands for diamond-lkike carbon coating, and is a nanocomposite coating that has unique properties of natural diamond low friction, high hardness, and high corrosion resistance. "Black Hills Ammunition has been making the most accurate and lethal 5.56 cartridges for years. In particular, their 77 grain OTM or MK 262 variants as its known in the military has performed without fail for over 20 years. I have used it myself and consider it lifesaving equipment. As a military sniper I came into service when BH 77 grain was gaining favor with my community and also when my community began the concept of what's now known as the MK 12 5.56 light sniper rifle. Over the years and through many rounds, testing and evaluations I, along with others, discovered that a twist rate of 1/7.7 is the absolute best for optimizing performance from Black Hills 77 grain ammunition. Now thanks to BCMA(R) anyone can buy a complete upper tailor made for use with BH 77 grain variants." Kyle Defoor June 2017 About Kyle Defoor Kyle Defoor is a professional shooter who teaches firearms and tactics to military, law enforcement, and civilians. Specializing in pistol, carbine, urban sniper, and CQB, Kyle gained his knowledge from decorated combat service in multiple war fronts as a special operator and as one of the first and premier tactical trainers in the world. An active motorcyclist, hunter, climber, runner, and waterman he can be seen on multiple TV shows, magazines, websites, and on ranges worldwide.Please visit Defoor Proformance Shooting Shop Related Products: Want to see more upper receivers? Click the links below to view more BCMA(R) AR complete uppers! 16" Recce Mid Length AR-15 Complete Uppers AR-15 Complete Uppers w/ QRF(TM) Handguards 16" Mid Length AR-15 Complete Uppers BCMA(R) Kyle Defoor Complete Uppers All BCMA(R) AR-15 Complete Uppers Bravo Company builds: Life Saving Tools(TM) Copyright 2023 Bravo Company MFG, Inc.