Quattro-15 Series.
Rifles and pistols built by the SOT Custom Shop on Desert Tech’s Quattro-15 lower, in two families: HM Defense Monobloc® direct impingement and short-stroke piston. Fifty-three rounds in the QMAG-53, and any standard STANAG magazine through the included adapter.
Their capacity. Our architecture. One rifle.
← All firearmsChoose the operating system first
Both families share the Quattro-15 lower, the QMAG-53 and Bombproof by Design™. What changes is how the upper runs, and each is offered as a rifle and a pistol.
Quattro-15 Monobloc®
An HM Defense Monobloc® barrel, its gas block milled into the barrel blank, thermal fitted to SOT’s MOD-0 forged upper and run by the SOT Enhanced HMB™ bolt carrier group.
- Rifles: two 16″ RECCE builds and the 16″ A5 rifle
- Short Barrel Rifles: a 12.5″ RECCE build
- Pistols: a 12.5″ A5 build with the SBA5® brace
Quattro-15 816
A Caracal CAR816 short-stroke piston upper with SOT enhancements, on the same Quattro-15 lower. Gas stays forward, out of the receiver.
- Rifles: 16″, in FDE Cerakote® or black anodized
- Short Barrel Rifles: an 11.5″ build
- Pistols: an 11.5″ build with the SBA5® brace
Quattro-15 Monobloc® Rifles and Pistols
16″ Quattro-15 Monobloc® RECCE Rifle — FDE Cerakote®
FDE Cerakote® upper, handguard and lower, with Reptilia RECC·E™ furniture to match.
16″ Quattro-15 Monobloc® RECCE Rifle — Black Anodized
Black anodized upper, handguard and lower, with black Reptilia RECC·E™ furniture.
16″ 5.56 NATO Quattro-15 Monobloc® A5 Rifle
The Monobloc® upper on a VLTOR A5 with A5H2 buffer and B5 Systems furniture, black only. Choose a 15″ or 13″ M-LOK handguard or the 13″ Picatinny quad rail, and a chrome-lined or standard bore.
12.5″ Quattro-15 Monobloc® RECCE Short Barrel Rifle
The same 12.5″ Monobloc® upper as the A5 pistol, on the RECCE configuration: carbine buffer, Reptilia RECC·E™ stock and CQG™ grip.
12.5″ 5.56 NATO Quattro-15 Monobloc® A5 Pistol
The Monobloc® upper with mid-length gas at 12.5″, thermal fitted to the MOD-0 forged receiver, with a VLTOR A5, CN5F castle nut and SB Tactical SBA5® brace.
What every Monobloc® build carries
Thermal fitted Monobloc®
HM Defense Monobloc® barrel, thermal fitted to the MOD-0 forged upper, with the gas block milled straight into the barrel blank: 16″ on the rifles, 12.5″ with mid-length gas on the short barrel rifle and pistol.
SOT Wedge-Lock handguard
Free float, with a full-length top Picatinny rail: 15″ M-LOK on the RECCE rifles, 15″ or 13″ M-LOK or a 13″ Picatinny quad rail on the A5 rifle, 11.7″ M-LOK on the short barrel rifle and pistol.
SOT Enhanced HMB™ group
The HMB™ bolt in SOT’s enhanced carrier, black nitride, with an index-marked gas key. Standard; chrome groups are optional.
Suppressor-ready on request
Ships with the A2 Extended Flash Hider. Order any of the Faxon MuzzLok® brakes and the rifle is ready for a suppressor; the MuzzLok® removes for a direct-mount can.
RECCE or A5: what changes by build
RECCE builds
The 16″ RECCE rifles (FDE and black) and the 12.5″ RECCE short barrel rifle. Reptilia RECC·E™ Carbine stock and CQG™ grip on a carbine-length buffer system with an H2 buffer. The 16″ rifles have a chrome-lined bore.
A5 builds
The 16″ A5 rifle and the 12.5″ A5 pistol. VLTOR A5 receiver extension with an A5H2 buffer and a B5 Systems Type 23 grip with grip plug: the B5 Systems Enhanced SOPMOD stock on the rifle, the SB Tactical SBA5® brace on the pistol. The rifle is ordered with a chrome-lined or standard bore and a choice of three handguards.
Quattro-15 816 Rifles, Short Barrel Rifles and Pistols
16″ 5.56 NATO Quattro-15 816 Short-Stroke Piston Rifle — FDE Cerakote®
The SOT816E enhanced piston upper on the Quattro-15 lower, FDE Cerakote® throughout, with a VLTOR A5 and CN5F castle nut and B5 Systems furniture.
16″ 5.56 NATO Quattro-15 816 Short-Stroke Piston Rifle — Black Anodized
The same 16″ rifle in black anodized, with black B5 Systems furniture.
11.5″ 5.56 NATO Quattro-15 816 Short-Stroke Piston Short Barrel Rifle
The SOT816E enhanced piston upper, with the HMB™ bolt Caracal does not sell, on the Quattro-15 lower. Law Tactical folder, Magpul DT stock.
11.5″ 5.56 NATO Quattro-15 816 Short-Stroke Piston Pistol
The SOT816E enhanced piston upper on the Quattro-15 lower, with an SB Tactical SBA5® brace and a B5 Systems Type 23 grip.
What the 816 builds carry
SOT816E enhanced upper
A Caracal CAR816 with the HMB™ bolt in place of the platform’s bolt, running in Caracal’s anti-tilt piston carrier, with a laser-engraved arrow index-marked cam pin, and a caliber-marked ejection port cover.
Three-position regulator, no gas key
Gas stays forward at the regulator (normal, adverse, suppressed). A piston carrier has no gas key, so there are no gas key screws to loosen.
Caracal barrel and 9.1″ rail
4150 CMV, QPQ black nitride, 1:7 twist, with Caracal’s barrel extension and extractor support pin, under a 9.1″ Caracal M-LOK handguard.
Suppressor-ready as shipped
The removable Faxon MuzzLok® Gunner 3-port is standard: take it off for a direct-thread 1/2×28 suppressor and set the regulator to suppressed.
VLTOR A5 recoil system
The 816 runs the A5 system only. The 11.5″ short barrel rifle and pistol run the A5H1 buffer; on the short barrel rifle it is stepped down from A5H2 to suit the Law Tactical folder.
Furniture by build
B5 Systems Enhanced SOPMOD and Type 23 grip, with the B5 Systems grip plug, on the 16″ rifles; Magpul DT stock on the short barrel rifle; SB Tactical SBA5® brace and B5 Systems Type 23 grip, with the grip plug, on the pistol.
What every build in the series carries
Fifty-three rounds, or any STANAG magazine
Every Quattro-15 ships with a Desert Tech QMAG-53 and the Quattro-15 Magwell Adapter Kit (P/N ACC0292), which lets the dedicated quad-stack lower accept standard USGI and AR-15 / STANAG pattern 30-round magazines. No proprietary-magazine lock-in.
HM Defense HMB™ bolt
On both families: a cam pin socket instead of a through-hole at the bolt’s most heavily loaded point, with SOT’s arrow-indexed cam pin on the standard groups.
LaRue Tactical MBT-2S
The two-stage trigger on the series, curved bow standard, straight bow at no upcharge.
Ambidextrous controls
Radian Talon selector, Desert Tech’s proprietary ambidextrous bolt and magazine releases, an integrated trigger guard forged into the lower and an integrated QD sling socket.
Make it yours
| Option | Detail | Price |
|---|---|---|
| Monobloc® builds: RECCE rifles, A5 rifle, RECCE short barrel rifle and A5 pistol | ||
| A2 Extended Flash Hider | Black Cerakote®, standard | Included |
| 4-port hardened flash hider | Black Cerakote® | +$40.00 |
| Faxon MuzzLok® Gunner 3-port brake | 5.56, steel; removes for a direct-mount suppressor | +$60.00 |
| Faxon MuzzLok® stainless steel Plan B brake | Plan B suppressor interface | +$75.00 |
| Magpul MBUS 3 sight set | Front & rear flip-up, black (MAG1166-MAG1167): spring-loaded ambidextrous push-button deploy, tool-less front elevation, rapid-select rear aperture | +$75.00 |
| Chrome bolt carrier group | Young Manufacturing M16 Chrome BCG with HMB™ bolt, in place of the standard SOT Enhanced HMB™ Black Nitride group. Supplied as Young build it, without SOT’s enhancements (no cam pin or gas key marks, gas key not staked) | +$149.00 |
| Chrome bolt carrier group | Microbest Super-Stake C158 all-chrome BCG, heavy-duty stake, with chrome HMB™ bolt, in place of the standard SOT Enhanced HMB™ Black Nitride group | +$149.00 |
| LaRue MBT-2S bow | Curved (standard) or straight | No charge |
| 816 rifles, short barrel rifles and pistols | ||
| Faxon MuzzLok® Gunner 3-port brake | 5.56, steel, removable; standard | Included |
| Faxon MuzzLok® stainless steel Plan B brake | Plan B suppressor interface | +$75.00 |
| Magpul MBUS 3 sight set | Front & rear flip-up, black (MAG1166-MAG1167) | +$75.00 |
| LaRue MBT-2S bow | Curved (standard) or straight | No charge |
For other muzzle choices, contact us: we offer a wide variety, including mounts for many suppressor manufacturers and other Plan B options.
Where the Quattro-15 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. Colorado and Vermont restrict the 53-round QMAG-53 rather than the rifle; there, and wherever magazine-capacity limits apply, rifles ship with compliant magazines instead. Hawaii restricts the pistol variant.
Every firearm ships to your FFL dealer. Laws change: please confirm with your local FFL before ordering.
Who builds what
The Quattro-15 lower and the QMAG-53 are developed and manufactured by Desert Tech, and the 816 uppers are Caracal’s CAR816 platform with Second of Ten’s enhancements. The Monobloc® uppers, the pairings and the builds are Second of Ten’s, by the SOT Custom Shop in Stuart, Florida.
Photographed as built
Product photos and zoom viewers show the actual firearms, both sides, not renderings. Serial numbers are blurred.
Marks
MONOBLOC® and HMB™ are marks of HM Defense, LLC, used under license. Desert Tech, Quattro-15 and QMAG are marks of Desert Tech; RECC·E™ and CQG™ of Reptilia; Caracal and CAR816 of Caracal; MuzzLok® of Faxon Firearms; MBUS®, PMAG® and DT of Magpul; SBA5® of SB Tactical; Law Tactical of Law Tactical LLC; VLTOR of VLTOR Weapon Systems; CN5F of Forward Controls Design; B5 Systems of B5 Systems; ERGO of ERGO Grips; MBT-2S of LaRue Tactical; Cerakote® of NIC Industries. Their appearance indicates that Second of Ten incorporates the component, not sponsorship or endorsement.
The Quattro-15 lower and QMAG-53 are developed and manufactured by Desert Tech. Monobloc® and HMB™ are marks of HM Defense, LLC, used under license. Other product names are marks of their respective owners.
Bombproof by Design™
Precision // Purpose // Performance