These super match-grade barrels are not "drop in," so the gunsmith can precisely fit them to a specific slide/receiver pair for the tightest lockup and best accuracy results. They come short chambered, so reaming to achieve correct headspace is required, as is fitting of the hood, lugs and feet. But the special geometry of Nowlin's pre-cut top lugs typically requires only minor fitting to achieve maximum lug engagement. Groove and bore tolerances are held to an amazing .0002" via state-of-the-art electro-discharge cathode maching (ECM), and rifling is ultra-smooth, uniform and precise. Smooth-cut rifling boosts velocity, while the unique angled Mfg: Nowlin