11.5″ 5.56 NATO Quattro-15 816 Short-Stroke Piston Short Barrel Rifle
SOT816E enhanced upper · 9.1″ M-LOK handguard · Law Tactical folder · black anodized
11.5″ 5.56 NATO short-stroke piston barrel with a removable Faxon MuzzLok® Gunner 3-port 5.56 muzzle brake, on a SOT816E enhanced upper receiver (Caracal CAR816 with Second of Ten's enhancements) with a 9.1″ Caracal M-LOK handguard, paired with a Desert Tech Quattro-15 lower receiver with a Radian Talon ambidextrous selector, a LaRue Tactical MBT-2S curved-bow trigger, a VLTOR A5 receiver extension and A5 buffer, a Law Tactical folding stock adapter, a Magpul DT Carbine stock, an ERGO Original grip and a Desert Tech QMAG-53 quad-stack magazine. Black anodized.
// Specification
| Model | 11.5″ 5.56 NATO Quattro-15 816 Short-Stroke Piston Short Barrel RifleSKU QTR15-816E-B115-BLK-S (proposed) |
|---|---|
| Series | Quattro-15 · Short-stroke pistonShort barrel rifle |
| Chambering | 5.56×45mm NATO.223 Remington compatible |
| Barrel | 11.5″, 4150 CMV, QPQ black nitrideModified M4 contour · Caracal barrel extension and chamber, with extractor support pin |
| Twist | 1:7 |
| Muzzle thread | 1/2×28 |
| Gas system | Short-stroke piston, three-position regulatorNormal · adverse · suppressed. Gas stays forward, out of the receiver |
| Muzzle device | Faxon MuzzLok® Gunner 3-port 5.56 steel muzzle brakeStandard and removable · optional: Faxon MuzzLok® stainless steel Plan B brake (+$75) · other choices on inquiry, including mounts for many suppressor manufacturers and other Plan B options |
| Suppressor | Suppressor-ready as shippedRemove the MuzzLok® for a direct-thread 1/2×28 suppressor; set the regulator to suppressed. No buffer swap, no adapter |
| Upper receiver | SOT816E: Caracal CAR816 with Second of Ten enhancementsForged 7075, hard-coat anodized |
| Forward assist | YesPhosphate finish |
| Handguard | 9.1″ Caracal M-LOKKey-lock anti-cant interface · integrated QD points · full-length top Picatinny rail |
| Bolt | HM Defense HMB™ bolt, nitrideFitted in place of the platform's Carpenter 158 bolt · laser-engraved arrow index-marked radiused cam pin |
| Bolt carrier | Caracal anti-tilt piston carrier, QPQLightning cuts for reduced reciprocating mass · no gas key |
| Charging handle | Ambidextrous |
| Ejection port cover | Caliber-marked, 5.56 NATO |
| Lower receiver | Desert Tech Quattro-15, black Type III hard-coat anodizedMachined from a 7075-T6 aluminum forging |
| Lower rollmark | MULTI-CALThe rifle is chambered 5.56 NATO; MULTI-CAL is the receiver's marking |
| Trigger guard | IntegratedForged into the lower receiver |
| Safety selector | Radian Talon, ambidextrousBlack |
| Bolt release | Desert Tech proprietaryAmbidextrous |
| Magazine release | Desert Tech proprietaryAmbidextrous · standard on every Quattro-15 |
| Pivot pins | NitrideSOT standard |
| Sling mount | Integrated QD sling socketLeft side of the receiver |
| Tension screw | Upper receiver tensioning set screwDesert Tech's design · fit and feel, not accuracy |
| Trigger | LaRue Tactical MBT-2S, curved bowTwo-stage · straight bow also available · the only trigger offered on the Quattro-15 series |
| Recoil system | VLTOR A5 receiver extension, A5H1 buffer, A5 rifle-length springBuffer stepped down from A5H2 to suit the folder · A5 only on the 816 |
| Folding adapter | Law Tactical AR Folding Stock AdapterFolds to the left · adds 1.3″ to length of pull · the rifle will not cycle folded |
| Stock | Magpul DT CarbineBlack |
| Grip | ERGO OriginalBlack |
| Sights | None standardOptional: Magpul MBUS 3 front & rear flip-up set (MAG1166-MAG1167), black · spring-loaded, ambidextrous push-button deploy · tool-less front elevation · rapid-select rear aperture · 0.44″ folded · +$75.00 |
| Magazine | Desert Tech QMAG-5353-round quad stack |
| Magwell adapter | Desert Tech Quattro-15 Magwell Adapter KitP/N ACC0292 · included · accepts standard USGI and AR-15/STANAG 30-round magazines |
| Case | 42″ Plano SE rifle case, blackEvery build ships in it · high-density molded polymer · high-density interlocking foam |
| Finish | Black anodized upper, handguard and lower receiverBarrel QPQ black nitride · furniture black |
// Ordering
Trigger: LaRue MBT-2S, curved bow as shown or straight bow, no upcharge. Ships with the removable Faxon MuzzLok® Gunner 3-port brake. Optional: Faxon MuzzLok® stainless steel Plan B brake +$75. Ask about other choices: we offer a wide variety, including mounts for many suppressor manufacturers and other Plan B options.
Optional sights: Magpul MBUS 3 front & rear set (MAG1166-MAG1167), black, +$75.
Their capacity. Our architecture. One rifle.
The Quattro-15 lower and the QMAG-53 magazine are developed and manufactured by Desert Tech, and the receiver is rollmarked and serialised by them as the model of record. The upper is Caracal's CAR816 platform. Second of Ten claims none of that engineering. What is ours is the pairing, a short-stroke piston upper on the Quattro-15 lower, and the enhancements to the upper.
The 816, with the bolt Caracal doesn't sell
The SOT816E is a Caracal CAR816 upper with three Second of Ten enhancements: an HM Defense HMB™ bolt, nitride finished, running in the Caracal piston carrier; a laser-engraved arrow index-marked radiused cam pin; and a caliber-marked ejection port cover. A standard AR bolt has its cam pin hole drilled straight through at its most heavily loaded point. The HMB™ bolt uses a cam pin socket instead, retaining material where a standard bolt gives it up.
No gas key to loosen
A piston carrier has no gas key, so there are no gas key screws to back out, the failure an index mark exists to catch on a direct-impingement group. The gas stays forward at the regulator, and the three positions (normal, adverse, suppressed) let the rifle run clean or suppressed.
What the platform was tested to
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.
The folder is a tuning decision, not a hinge
The Law Tactical adapter hinges at the receiver and adds a bolt carrier extension to the reciprocating mass, so Second of Ten steps the A5 buffer down from A5H2 to A5H1 to compensate. Folded, the rifle will fire once but will not cycle: treat a folded rifle as stowed, not as ready, and close the stock before firing.
Fifty-three rounds, or any STANAG magazine
The rifle ships with one QMAG-53 and Desert Tech's Quattro-15 Magwell Adapter Kit (P/N ACC0292). The adapter lets the dedicated quad-stack Quattro-15 lower accept standard USGI and traditional AR-15 / STANAG pattern 30-round magazines, from a Magpul PMAG® to aluminum GI. No proprietary-magazine lock-in.
A short barrel rifle
This is a short barrel rifle. It is not an ordinary Title I rifle, it is not transferred the same way, and it is not lawful for every buyer everywhere.
Where this rifle can ship
The Quattro-15 cannot be sold in California, Connecticut, Delaware, Illinois, Maryland, Massachusetts, New Jersey, New York, Rhode Island, Washington or Washington, D.C., under assault-weapon or feature-test restrictions. 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.
The trigger: LaRue Tactical MBT-2S
The LaRue Tactical MBT-2S is the trigger on the Quattro-15 series: a two-stage trigger with a light take-up and a clean second stage. This rifle carries the curved bow; the straight bow is also available. Second of Ten does not stone, polish or modify sear engagement surfaces.
Ships in a hard case
Every Quattro-15 build ships in a 42″ black Plano SE rifle case: high-density molded polymer construction with high-density interlocking foam, so it arrives protected and you have a case for transport from day one.
Photographed as built
These are photographs of this rifle, not renderings, taken on both sides. Zoom in to read the rollmarks, machining and fit. The serial number is blurred.
Photography © Second of Ten LLC. 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; MuzzLok® of Faxon Firearms; Talon of Radian Weapons; MBT-2S of LaRue Tactical; VLTOR of VLTOR Weapon Systems; Law Tactical of Law Tactical LLC; DT, PMAG® and MBUS® of Magpul Industries; ERGO of ERGO Grips. Marks are the property of their owners; their appearance indicates that Second of Ten incorporates the component, not sponsorship, affiliation or endorsement.