SOTM4A5 Forged Series.
The HM Defense Monobloc® rifle on a forged receiver set: the same Monobloc® barrels, mid-length gas and SOT Enhanced HMB™ bolt carrier group as our flagship SOTM4A5 billet rifles, on a MOD-0 forged upper and an SOTM4 forged lower. Every rifle is fully gauged and function tested, including test firing, before it ever leaves our facility.
Forged on both halves. The gas block is part of the barrel.
← All firearmsThe step down in price, not in the parts that keep it running.
The SOTM4A5 Forged Series is the Monobloc® rifle from our billet flagship, built on a forged receiver set. The barrel, the gas system, the bolt carrier group and the recoil system are the same. The upper and lower are forged 7075, and the barrel is thermal fitted to the forged MOD-0 upper. It costs less because a forging takes less machine time than billet, not because anything that keeps the rifle running was taken out. From $1,450.00.
Forged
Strength from the grain
Pressed to shape, so the grain follows the receiver: stronger and tougher than billet of the same alloy.
Thermal fitted
A barrel joint that holds itself
An interference fit between receiver and barrel extension, with no compound and no bedding.
Bombproof by Design™
Failure points removed
A gas block that can’t loosen, a bolt that keeps its metal, a gas key you can read, a recoil system that stays put.
The step down from the billet flagship, and what it changes
We build both, so we have no reason to sell you one by running down the other. Both are 7075 aluminum; what differs is how the receiver is made. Forging presses the metal into shape, so its grain follows the receiver: forged is the stronger of the two, and the tougher against impact and hard use. Billet is machined from a solid block, which holds far tighter tolerances between upper and lower and leaves room for SOT’s own profile and ambidextrous controls, at more machine time and a higher price.
| SOTM4A5 Forged Series | SOTM4A5 billet rifles and pistols (flagship) | |
|---|---|---|
| Strength and fit | Forged: grain follows the shape of the receiver, the stronger and more impact-resistant of the two. Mil-Spec dimensions, fits across brands | Billet: machined from a solid block, with far tighter tolerances between upper and lower |
| Receivers | MOD-0 forged upper and SOTM4 forged lower | SOT billet upper and SOTM4 billet lower, SOT profile styling with the left-side relief cut |
| Barrel joint | Monobloc® barrel thermal fitted to the forged upper: no compound, no bedding | Monobloc® barrel in the billet upper |
| Barrel, gas and bolt | The same on both: HM Defense Monobloc®, mid-length gas with the gas block milled into the barrel blank, SOT Enhanced HMB™ bolt carrier group | |
| Bolt release | Left side only (Geissele Maritime) | Ambidextrous, with a right-side release |
| Standard trigger | Schmid Inside Elite two-stage, DLC; G2S® or LaRue MBT-2S +$100 | LaRue MBT-2S or Geissele G2S® |
| Lineup | 16″ rifle (M-LOK or quad rail, FDE or black), 14.5″ and 13.9″ chrome-lined and 12.5″ short barrel rifles | Rifles, short barrel rifles and pistols, 12.5″ to 16″ |
| Price | From $1,450.00 | See the flagship series |
SOTM4A5 Forged Rifles and Short Barrel Rifles
16″ SOTM4MBA5 Forged Rifle
The 16″ Monobloc® on the forged receiver set. Choose a 15″ or 13″ SOT Wedge-Lock M-LOK handguard, FDE or black, or the 13″ Picatinny quad rail in black (FDE coming soon).
14.5″ SOTM4MBA5 Forged Short Barrel Rifle, Chrome-Lined, 13″ M-LOK
A 14.5″ chrome-lined Monobloc® under a 13″ SOT Wedge-Lock M-LOK handguard, black. Under ATF’s October 9, 2026 guidance no NFA registration is required; state law still applies.
13.9″ SOTM4MBA5 Forged Short Barrel Rifle, Chrome-Lined, 13″ M-LOK
A 13.9″ chrome-lined Monobloc® in Black Phosphate under a 13″ SOT Wedge-Lock M-LOK handguard, black. Under ATF’s October 9, 2026 guidance no NFA registration is required; state law still applies.
12.5″ SOTM4MBA5 Forged Short Barrel Rifle, 11.7″ M-LOK
A 12.5″ Monobloc® that still reaches mid-length gas, under an 11.7″ SOT Wedge-Lock M-LOK handguard, black. Under ATF’s October 9, 2026 guidance no NFA registration is required; state law still applies.
The forged lower, sold complete
SOTM4MOD1 A5 Forged Complete Lower Receiver
The SOTM4MOD1 A5 forged lower the rifles are built on, sold complete: Schmid two-stage DLC trigger, Geissele Posi-Snap and Maritime, SOT A5 nine-position tube, A5H2, B5 Systems Bravo in FDE or black. Upper not included.
Why a forged receiver set
Stronger where an AR takes its knocks
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 receiver of the same alloy, and tougher against impact and hard use.
Fits like every Mil-Spec receiver
Both forged receivers are held to Mil-Spec dimensions, so they work with Mil-Spec parts across brands. The SOTM4MOD1 A5 complete lower, sold on its own, pairs with any Mil-Spec AR-15 upper.
Priced for the machine time it saves
A forging comes out close to its finished shape, so it needs far less machining than billet. That is where the price difference comes from. Billet buys tighter tolerances between upper and lower and room for features like SOT’s profile and an ambidextrous bolt release. We build both.
A barrel joint that holds itself
On most AR rifles the barrel is held in the upper by the barrel nut: the extension slides into the receiver and the nut clamps it. On the MOD-0 forged upper we fit the barrel thermally, so the receiver itself grips the barrel extension.
How it is done
The upper receiver is expanded with heat and the barrel extension chilled, so the two seat without force. As they return to the same temperature, the receiver closes on the extension in an interference fit.
What it gives you
A barrel joint that does not depend on the barrel nut’s clamping force alone to keep the barrel square to the receiver. No galling on assembly, no retaining compound, no bedding.
Why it suits the forged upper
MOD-0 is how Second of Ten designates a thermal-fitted receiver: it names how the barrel is held. On this series it is the forged upper, so a forged receiver set carries the same disciplined barrel joint as our other MOD-0 builds.
Thermal fitting secures the joint. It is not a group-size promise: accuracy comes from the barrel, the ammunition and the shooter.
Four failure points, removed at the component
Bombproof by Design™ is how we choose parts: find the documented failure points on an AR, and remove them at the component instead of managing them with maintenance. The forged series carries the same four answers as our billet flagship.
The gas block that cannot come loose
On an HM Defense Monobloc® the gas block is milled straight into the metal of the barrel blank during manufacturing. There is no separate block to clamp, pin or set-screw, nothing to shift, and no port to misalign. The port is sized at manufacture for mid-length gas, even at 12.5 inches.
The bolt that keeps its metal
The cam pin hole is the documented weak point of the AR bolt. The HMB™ bolt replaces the through-hole with a socket, so material is retained where a standard bolt removes it. Its radiused cam pin carries the SOT arrow index, so it always goes back in the same way, for even wear and longer cam pin life.
A gas key you can check at a glance
The gas key is staked, and a single line is laser engraved across the key and both screw heads. A screw that has started to turn shows as a stepped line during ordinary cleaning, long before it can leak gas and short-stroke the rifle. If the line is broken, contact us before firing.
A recoil system that stays put
The SOT A5 nine-position buffer tube runs an A5H2 buffer and a rifle-length action spring: the same energy over a longer runway, for a lower peak. The Forward Controls Design CN5F extended castle nut is staked, with Vibra-TITE VC-3 on the threads, so the tube cannot back out.
The trade-off we accept: a Monobloc® gas port is sized at manufacture, so it cannot take an adjustable gas block.
Lengths, weights and prices
| Model | Barrel | Handguard | Length, collapsed / extended | Weight, unloaded | Price |
|---|---|---|---|---|---|
| 16″ SOTM4MBA5 Forged RifleRifle | 16″ HM Defense Monobloc® | 15″ M-LOK · 13″ M-LOK · 13″ Quad Rail (FDE quad rail coming soon) FDE or black | 34″ / 37″ | 6 lb 15 oz / 6 lb 11 oz / 7 lb 11 oz | $1,450.00 – $1,500.00 |
| 14.5″ SOTM4MBA5 Forged Short Barrel RifleShort barrel rifle | 14.5″ HM Defense Monobloc®, chrome-lined | 13″ M-LOK, black | 32.5″ / 36″ | 6 lb 8 oz | Price soon |
| 13.9″ SOTM4MBA5 Forged Short Barrel RifleShort barrel rifle | 13.9″ HM Defense Monobloc®, chrome-lined | 13″ M-LOK, black | 31.9″ / 35.4″ | 6 lb 7 oz | Price soon |
| 12.5″ SOTM4MBA5 Forged Short Barrel RifleShort barrel rifle | 12.5″ HM Defense Monobloc® | 11.7″ M-LOK, black | 31.5″ / 34″ | 6 lb 6 oz | $1,450.00 |
| SOTM4MOD1 A5 Forged Complete Lower ReceiverComplete lower receiver | The forged lower the series is built on, sold complete: Schmid two-stage DLC trigger, Geissele Ambi Posi-Snap and Maritime, SOT A5 nine-position tube, A5H2, B5 Systems Bravo stock and grip in FDE or black. Upper not included. | $625.00 | |||
Every rifle: 5.56×45mm NATO (.223 Remington compatible), 4150 chrome-moly, match-grade, triple-honed, button-rifled, 1:8, mid-length gas · SOT Enhanced HMB™ group in black nitride · one 30-round magazine: Lancer L5AWM® with FDE builds, to match; Magpul PMAG® 30 GEN M3™, SOT crest engraved, with black builds · Breek Arms WARHAMMER charging handle · forward assist · Schmid Inside Elite two-stage trigger · Geissele Ambi Posi-Snap and Maritime · B5 Systems Bravo stock and Type 23 grip.
What every SOTM4A5 forged rifle and short barrel rifle carries
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 tube, so you can read the setting at a glance and return to it. A5H2 buffer and A5 rifle-length spring, Forward Controls Design CN5F extended castle nut, staked, with Vibra-TITE VC-3 on the threads.
Thermal fitted Monobloc®
HM Defense Monobloc®, 16″, 14.5″ or 13.9″ chrome-lined, or 12.5″, 4150 chrome-moly steel, match grade, triple-honed and button-rifled, 1:8. The gas block is milled straight into the barrel blank, and the barrel is thermal fitted to the MOD-0 forged upper.
SOT Enhanced HMB™ group
The HMB™ bolt, with a cam pin socket in place of the through-hole, in SOT’s enhanced carrier: black nitride, arrow-indexed cam pin, staked and index-marked gas key. Chrome groups are optional.
Schmid two-stage trigger
Schmid Inside Elite two-stage, DLC, curved bow: 3.5 lb total. The Geissele G2S® or LaRue Tactical MBT-2S can be installed instead for $100.00.
Geissele controls
Ambi Posi-Snap selector and Maritime bolt catch on the SOTM4MOD1 A5 lower, with a button magazine release, nitride takedown and pivot pins, and a B5 Systems Bravo aluminum trigger guard.
Caliber on the port cover
The ejection port cover is engraved and filled MONOBLOC · 5.56 NATO on both faces, so the chambering reads with the cover shut or open.
Suppressor-ready on request
Ships with the A2 Extended Flash Hider. Order either Faxon MuzzLok® brake and the rifle is ready for a suppressor; the MuzzLok® removes for a direct-mount can.
Make it yours
| Option | Choice | Price |
|---|---|---|
| Trigger | Schmid Inside Elite 2-Stage, DLC, curved bow (standard) | Included |
| Trigger | Geissele Automatics G2S® two-stage, installed | +$100.00 |
| Trigger | LaRue Tactical MBT-2S two-stage, curved or straight bow, installed | +$100.00 |
| Muzzle device | A2 Extended Flash Hider, Black Cerakote® (standard) | Included |
| Muzzle device | 4-port hardened flash hider, Black Cerakote® | +$40.00 |
| Muzzle device | Faxon MuzzLok® Gunner 3-port 5.56 steel muzzle brake | +$60.00 |
| Muzzle device | Faxon MuzzLok® stainless steel Plan B muzzle brake | +$75.00 |
| Bolt carrier group | SOT Enhanced HMB™, Black Nitride (standard) | Included |
| Bolt carrier group | Young Manufacturing M16 Chrome BCG with HMB™ bolt (supplied as Young build it, without SOT’s enhancements) | +$149.00 |
| Bolt carrier group | Microbest Super-Stake C158 all-chrome BCG, heavy-duty stake, with chrome HMB™ bolt | +$149.00 |
| Sights | Magpul MBUS 3 front & rear flip-up set, black (MAG1166-MAG1167) | +$75.00 |
For other muzzle choices, contact us: we offer a wide variety, including mounts for many suppressor manufacturers and other Plan B options. Each product has a printable sell sheet with the full specification, linked from its tile above.
Not a black rifle upgrade. A correction.
The Monobloc® rifle from our billet flagship, on a forged, thermal-fitted receiver set. From $1,450.00.
Where the SOTM4A5 forged rifles can ship
Not available in California, Connecticut, Delaware, Illinois, Maryland, Massachusetts, New Jersey, New York, Rhode Island, Washington or Washington, D.C. The short barrel rifles are also not available in Hawaii. In Colorado and Vermont, and wherever magazine-capacity limits apply, they ship with compliant magazines instead of the 30-round magazine.
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.
Every firearm ships to your FFL dealer. Laws change: please confirm with your local FFL before ordering.
Two things it 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 billet builds carry one. Both are by design.
Photographed as built
Product photos and zoom viewers show the actual rifles, both sides, not renderings. Serial numbers are masked. Anodized shade varies from lot to lot.
Marks
MONOBLOC® and HMB™ are marks of HM Defense, LLC, used under license. Bombproof by Design™ is a mark of Second of Ten LLC. Geissele Automatics, G2S®, LaRue Tactical, MBT-2S, Schmid Inside, B5 Systems, Forward Controls Design, CN5F, Breek Arms, Lancer Systems, Magpul, MBUS®, PMAG®, Faxon, MuzzLok®, Vibra-TITE and Cerakote® marks are the property of their owners. Their appearance indicates that Second of Ten incorporates the component, not sponsorship or endorsement.
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