11.5″ 5.56 NATO Quattro-15 816 Short-Stroke Piston Short Barrel Rifle

Description

Their capacity. Our architecture. One rifle. The Quattro-15 lower and the QMAG-53 magazine are developed and manufactured by Desert Tech, and the upper is Caracal’s CAR816 platform. The pairing is ours: a short-stroke piston upper carrying Second of Ten’s enhancements, built by the SOT Custom Shop on the Quattro-15 lower. The 816, with the bolt Caracal doesn’t sell. Bombproof by Design™.

Open the zoom viewer: both sides of this rifle, photographed as built.

Short barrel rifle. This is not an ordinary Title I rifle, it is not transferred the same way, and it is not lawful for every buyer everywhere.

Barrel and Gas System

• 11.5″ 4150 CMV, QPQ black nitride, modified M4 contour
• 5.56×45mm NATO, .223 Remington compatible · 1:7 twist · 1/2×28 muzzle thread
• Caracal barrel extension and chamber, with extractor support pin
• Short-stroke piston with a three-position regulator: normal, adverse, suppressed. The gas stays forward, out of the receiver
• Faxon MuzzLok® Gunner 3-port 5.56 steel muzzle brake, standard and removable
• Optional add-on: Faxon MuzzLok® stainless steel Plan B muzzle brake, $75.00
• Other choices on inquiry: we offer a wide variety, including mounts for many suppressor manufacturers and other Plan B options. Contact us
• Suppressor-ready as shipped: the MuzzLok® removes cleanly to leave the 1/2×28 thread for a direct-thread suppressor, with the regulator set to suppressed. No buffer swap, no adapter

Upper Receiver: SOT816E

• Caracal CAR816 upper, forged 7075, hard-coat anodized, with three Second of Ten enhancements:
• HM Defense HMB™ bolt, nitride, fitted in place of the platform’s Carpenter 158 bolt: a cam pin socket instead of a through-hole, retaining material at the bolt’s most heavily loaded point
• Laser-engraved arrow index-marked radiused cam pin
• Caliber-marked ejection port cover (5.56 NATO)
• Caracal anti-tilt piston carrier, QPQ, with lightning cuts. No gas key, so no gas key screws to loosen
• Ambidextrous charging handle
• Forward assist, phosphate finish
• The CAR816 platform was engineered to NATO small-arms test protocols, including the catastrophic obstructed-bore test. That is a platform qualification this rifle inherits; Second of Ten did not conduct it and does not claim it as our own

Handguard

• 9.1″ Caracal M-LOK, key-lock anti-cant interface, integrated QD points, full-length top Picatinny rail

Lower Receiver

• Desert Tech Quattro-15, machined from a 7075-T6 aluminum forging, black Type III hard-coat anodized (rollmarked MULTI-CAL)
• Integrated trigger guard, forged into the lower
• Radian Talon ambidextrous safety selector, black
• Desert Tech proprietary ambidextrous bolt release and magazine release, standard on every Quattro-15
• Nitride pivot pins (SOT standard)
• Integrated QD sling socket on the left side of the receiver
• Upper receiver tensioning set screw (fit and feel, not accuracy)
• LaRue Tactical MBT-2S two-stage trigger, curved bow as shown or straight bow: the only trigger offered on the Quattro-15 series
• VLTOR A5 receiver extension, A5H1 buffer and A5 rifle-length spring. The 816 runs the A5 system only

Folder and Furniture

• Law Tactical AR Folding Stock Adapter: folds to the left and adds 1.3″ to length of pull
• The folder adds a bolt carrier extension to the reciprocating mass, so Second of Ten steps the A5 buffer down from A5H2 to A5H1 to compensate
• The rifle will not cycle folded. Treat a folded rifle as stowed, not as ready, and close the stock before firing
• Magpul DT Carbine stock, black
• ERGO Original grip, black

Extra Information

• Optional add-on: Magpul MBUS 3 front & rear flip-up sight set (MAG1166-MAG1167), black, $75.00: impact-resistant polymer, spring-loaded with an ambidextrous push-button, tool-less front elevation, rapid-select rear aperture, 0.44″ high folded, standard AR height deployed, Picatinny mount, made in the USA
• Ships with one Desert Tech QMAG-53 (53-round quad stack)
• Ships in a 42″ black Plano SE rifle case: high-density molded polymer, high-density interlocking foam
• Includes the Desert Tech Quattro-15 Magwell Adapter Kit (P/N ACC0292), which lets the dedicated quad-stack Quattro-15 lower accept standard USGI and traditional AR-15 / STANAG pattern 30-round magazines
• Not available in California, Connecticut, Delaware, Illinois, Maryland, Massachusetts, New Jersey, New York, Rhode Island, Washington or Washington, D.C.
• Colorado and Vermont restrict the 53-round QMAG-53: there, and wherever magazine-capacity limits apply, the rifle ships with compliant magazines instead
• Laws change: please confirm with your local FFL before ordering

HMB™ is a mark of HM Defense, LLC, used under license. Caracal and CAR816 are marks of Caracal; Desert Tech, Quattro-15 and QMAG are marks of Desert Tech. Their appearance indicates that Second of Ten incorporates the component, not sponsorship, affiliation or endorsement.