PRO2A 5.5" 40 S&W 1/16 Pistol Caliber Melonite M-LOK Upper Kit

Bring the hard-hitting barrier penetration and duty-proven ballistics of the .40 S&W cartridge to an ultra-compact AR footprint with the PRO2A 5.5" 40 S&W Pistol Caliber Melonite M-LOK Upper Kit. This 100% American-made master build bundle contains every critical component required to transform a standard stripped lower receiver into a finished tactical pistol or short-barreled rifle (PCC/SBR). Built around a premium 5.5-inch 4150 CMV steel barrel, this kit utilizes a highly reliable direct blowback system engineered to interface seamlessly with dedicated .40 S&W lower receivers or magazine conversion blocks. Complete with a pre-headspaced ramped blowback bolt carrier group, standard charging handle, complete lower parts kit (LPK), and a matching stabilizing pistol brace assembly, this all-inclusive package takes the technical guesswork out of building a hard-hitting defense tool.

Key Features

All-In-One Master Pistol Package: Eliminates component tracking and compatibility headaches by packaging the fully assembled .40 S&W upper, a ramped blowback BCG, a full lower parts kit, and a matching stabilizing brace group together.
Advanced Melonite Barrel Protection: The heavy-duty 4150 Chrome Moly Vanadium steel barrel is fully treated with an advanced Salt Bath Melonite finish inside the bore and across the exterior to maximize corrosion resistance and extend operational service life.
Optimal 1:16 Twist Rate: Precision button-rifled barrel geometry optimized to effortlessly stabilize popular 165gr and heavy-grain 180gr standard duty ammunition with consistent close-to-medium range accuracy.
Ramped Direct Blowback BCG: Features a premium, high-strength blowback bolt assembly designed with a ramped profile to work smoothly with standard AR-15 hammer setups and feed reliably from Glock-style or compatible profile magazines.
Ultra-Compact Free-Float M-LOK Rail: Machined from high-strength aluminum, the lightweight free-float handguard isolates barrel vibrations to preserve uniform mechanical accuracy while providing a continuous top rail and modular M-LOK spacing.
Complete Brace & LPK Hardware: Comes paired with a full Mil-Spec lower parts kit and a stabilizing pistol brace assembly equipped with a specialized heavy buffer to handle high-recoil blowback pressures.

Technical Specifications

Upper Receiver	Mil-Spec Billet Aluminum, Slick-Side Pistol Caliber Layout (No Forward Assist/Dust Cover), PCC Sized Ejection Port, Type III Hardcoat Anodized Black Finish
Bolt Carrier Group	Premium Ramped Direct Blowback BCG, High-Strength Steel Bolt Face, Nitride/Melonite Finish, Glock/Colt Magazine Compatible
Charging Handle	Standard Mil-Spec Aluminum Charging Handle Assembly
Barrel Component	5.5 Inch Profile, 4150 Chrome Moly Vanadium (CMV) Premium Steel, Melonite Treated Interior & Exterior Bore
Caliber	.40 S&W (Pistol Caliber)
Twist Rate	1:16 Twist
Operating System	Direct Blowback (Gas-less operation, no gas block or tube required)
Muzzle Device Component	Standard 9/16x24 Thread Pitch, A2 Birdcage Flash Hider with Crush Washer Pre-Installed
Handguard Rail	4 Inch Inch Slim Profile Free-Float Aluminum Handguard, Continuous Top Picatinny Alignment, Modular M-LOK Attachment Points
Lower Receiver Parts Kit (LPK)	Complete Mil-Spec Spring and Pin Kit, Polished Single-Stage Hammer and Trigger Assembly, Standard A2 Pistol Grip
Pistol Brace Extension Assembly	Stabilizing Pistol Blade, Pistol Buffer Tube, Specialized Heavy PCC Buffer, and High-Tensile Buffer Spring
Manufacturing Origin	100% Assembled and Quality Checked in the USA with Pro2A Tactical Lifetime Factory Warranty

Why Buy This Product?

Piecing together an AR-platform pistol caliber carbine (PCC) in .40 S&W from separate parts often exposes builders to frustrating cycling, extraction, or trigger resetting issues due to incorrect buffer weights and unmatched bolt geometry. The PRO2A 5.5" .40 S&W Upper Kit eliminates these hurdles out of the box. Every component in this master conversion package—from the pre-headspaced ramped blowback bolt group to the lower receiver internal hardware and specialized heavy pistol buffer—is meticulously curated by expert armorers to cycle reliably as a unified system. It offers defense-minded shooters an exceptionally compact, packable weapon system that shoots widely available duty ammunition without charging custom hardware or individual tuning premiums.