12.5″ SOTM4MBA5 Forged Short Barrel Rifle, 11.7″ M-LOK Black anodized · right and left side · drag to pan, scroll to zoom

CONFIGURATION SHOWN: 12.5″ HM Defense Monobloc® barrel, standard bore, with the standard A2 Extended Flash Hider in Black Cerakote®, thermal fitted to an SOT MOD-0 forged upper, 11.7″ SOT Wedge-Lock M-LOK handguard, black anodized, on an SOTM4MOD1 A5 forged lower with the Schmid Inside Elite two-stage trigger, Geissele Ambi Posi-Snap selector and Maritime bolt catch, button magazine release, nitride takedown and pivot pins, SOT A5 nine-position buffer tube with an A5H2 buffer, B5 Systems Bravo stock and Type 23 grip in black, and a Magpul PMAG® 30 GEN M3™ engraved with the SOT crest.

CONFIGURATION SHOWN: 12.5″ HM Defense Monobloc® barrel, standard bore, with the standard A2 Extended Flash Hider in Black Cerakote®, thermal fitted to an SOT MOD-0 forged upper, 11.7″ SOT Wedge-Lock M-LOK handguard, black anodized, on an SOTM4MOD1 A5 forged lower with the Schmid Inside Elite two-stage trigger, Geissele Ambi Posi-Snap selector and Maritime bolt catch, button magazine release, nitride takedown and pivot pins, SOT A5 nine-position buffer tube with an A5H2 buffer, B5 Systems Bravo stock and Type 23 grip in black, and a Magpul PMAG® 30 GEN M3™ engraved with the SOT crest.

Ordering. $1,450.00 · SKU MB-MBA5-B125-H117M-BLK-S. Trigger: Schmid Inside Elite 2-Stage, DLC, curved bow (standard) · Geissele Automatics G2S® two-stage, installed +$100 · LaRue Tactical MBT-2S two-stage, curved or straight bow, installed +$100. Muzzle device: A2 Extended Flash Hider, Black Cerakote® (standard) · 4-port hardened flash hider, Black Cerakote® +$40 · Faxon MuzzLok® Gunner 3-port 5.56 steel muzzle brake +$60 · Faxon MuzzLok® stainless steel Plan B muzzle brake +$75. Bolt carrier group: SOT Enhanced HMB™, Black Nitride (standard) · Young Manufacturing M16 Chrome BCG with HMB™ bolt (supplied as Young build it, without SOT's enhancements) +$149 · Microbest Super-Stake C158 all-chrome BCG, heavy-duty stake, with chrome HMB™ bolt +$149. Sights: Magpul MBUS 3 front & rear flip-up set, black (MAG1166-MAG1167) +$75. Short barrel rifle. Under ATF's October 9, 2026 guidance, a short barrel rifle no longer needs NFA registration or a tax stamp. State and local laws still apply, and some states prohibit short barrel rifles. Confirm with your FFL before ordering. Ships to your FFL dealer only.

The same Monobloc® rifle, on a forged receiver set. The barrel, the gas system, the bolt and the platform are the Monobloc® line as SOT builds it on billet. What changes in the SOTM4A5 Forged Series is the receiver set: a MOD-0 forged upper and a forged SOTM4 lower in place of the billet pair. That is the whole difference, and the reason the price steps down.

What forged buys: strength. Forging presses the 7075 aluminum into shape instead of cutting the receiver out of a solid block, so the grain of the metal follows the shape of the part. That makes a forged receiver stronger than a billet one, and tougher against impact and hard use. A forged MOD-0 pair is also held to Mil-Spec dimensions, so it fits like every other Mil-Spec receiver, and the Monobloc® barrel is thermal fitted to the upper, with no retaining compound and no bedding. What billet gives instead is tighter tolerances and design freedom.

The gas block is part of the barrel. On a Monobloc® the gas block is milled straight into the metal of the barrel blank during manufacturing, so there is no separate block to clamp, pin or set-screw, and nothing to shift. The port is sized at manufacture for mid-length gas, even at 12.5 inches, which also means the gas cannot be tuned.

The HMB™ bolt, with SOT's marks. The HM Defense HMB™ bolt replaces the cam pin through-hole with a socket, keeping material at the bolt's most heavily loaded point. SOT adds an arrow index to the cam pin, so it always goes back in the same direction for better wear and cam pin life, and an index line across the staked gas key screws.

A two-stage trigger as standard. The Schmid Inside Elite two-stage in DLC is the standard trigger: 3.5 lb total, 2.0 lb to the wall and 1.5 lb to break. The Geissele G2S® or the LaRue Tactical MBT-2S can be installed instead, for $100.00 more. Second of Ten does not stone, polish or modify sear engagement surfaces.

Numbered stock positions. The SOT A5 buffer tube has nine positions, with numeric index marks 1 through 8 laser engraved on it. The B5 Systems Bravo stock has a window over the extension, so you can read the setting at a glance and return to it.

Two things this short barrel rifle does not have. It cannot take an adjustable gas block: gas is set by the port at manufacture. And there is no right-side bolt release: the bolt catch is the Geissele Maritime, a left-side control. The billet builds carry a right-side release; this one does not, by design.

Where this short barrel rifle can ship. Under ATF's October 9, 2026 guidance, a short barrel rifle no longer needs NFA registration or a tax stamp. State and local laws still apply, and some states prohibit short barrel rifles. Confirm with your FFL before ordering. Not available in California, Connecticut, Delaware, Illinois, Maryland, Massachusetts, New Jersey, New York, Rhode Island, Washington or Washington, D.C. In Colorado and Vermont, and wherever magazine-capacity limits apply, it ships with compliant magazines instead of the 30-round magazine. Laws change: please confirm with your local FFL before ordering.

Photographed as built. These are photographs of the short barrel rifle, not renderings, taken on both sides. Zoom in to read the rollmarks, machining and fit. The serial number is masked; the address rollmark is not. Some lowers photographed carry SAFE / SEMI / AUTO selector markings for appearance only: every Second of Ten rifle is semi-automatic, with a semi-automatic trigger.

Photography © Second of Ten LLC. MONOBLOC® and HMB™ are marks of HM Defense, LLC, used under license. Bombproof by Design™ is a mark of Second of Ten LLC. Cerakote® is a mark of NIC Industries; G2S®, Posi-Snap and Maritime of Geissele Automatics; MBT-2S of LaRue Tactical; Inside Elite of Schmid Inside; WARHAMMER of Breek Arms; CN5F of Forward Controls Design; Bravo and Type 23 of B5 Systems; L5AWM® of Lancer Systems; PMAG®, GEN M3™ and MBUS® of Magpul Industries; MuzzLok® of Faxon Firearms; Vibra-TITE of ND Industries; M-LOK® of Magpul Industries. Marks are the property of their owners; their appearance indicates that Second of Ten incorporates the component, not sponsorship, affiliation or endorsement.