Maxim Defense MDX-510 Comfort and compactness, the 10.3" barrel length of the MDX-510 has always been a staple for CQB firearms. The MDX series was designed and tested to handle the fierce demands of the Tier 1 community. The right upgrades, features, and technology make sure the MDX-510 will stand up to whatever you put it through. Each MDX-510 is supplied with a Gen 7 CQB stock or Gen 6 CQB brace. The CQB system combines form and function flawlessly. Adding just 5.3" to the receiver when fully compact, yet extending fully to 10", you get a compact package with the full length-of-pull of standard carbine stocks. Our MDX series firearms are also equipped with the Maxim's HATEBRAKE muzzle booster. This patent-pending device significantly reduces recoil, decreases the flash signature, pushes gasses and concussion waves downrange away from the operator and improves overall performance in short barrel pistols and rifles.