# Second of Ten

> Precision Firearms Manufacturer


## Pages

- [M5 DI Series](https://sotarms.com/firearms/m5-di-series/): Our large-frame SOTM5 platform, running direct impingement, for full-power cartridges.
- [M4 Short Stroke Piston Series](https://sotarms.com/firearms/m4-short-stroke-piston-series/): Short-stroke piston rifles and pistols — our most sought-after line — including the SOT Enhanced CAR816E and the SOT QUATTRO-816 on the Desert Tech Quattro-15 lower.
- [M4 DI Series](https://sotarms.com/firearms/m4-di-series/): Our small-frame AR on the SOTM4 platform, running direct impingement — the SOTM4 Billet and SOTM4 Forged rifles and pistols, the SOT SPIRE 6, and the home of the SOTM4 Monobloc, our gold standard for bombproof design.
- [Support](https://sotarms.com/support/): Gauged and test fired before it ships — and answered after.
- [Contact](https://sotarms.com/contact/): We answer same day in most cases, and within 24 hours of receipt at the outside.
- [About SOT](https://sotarms.com/about-sot/): We don’t just build firearms. We engineer solutions.
- [Warranty Information](https://sotarms.com/warranty-information/): How our warranty works and what to do if you need to send something back. We stand behind what we build.
- [Terms of Sale](https://sotarms.com/terms-of-sale/): A plain-English guide to what applies when you buy a firearm, component, or accessory from Second of Ten.
- [FAQ](https://sotarms.com/faq/): If your question is not here, our support team answers same day in most cases.
- [Featured Firearms](https://sotarms.com/featured-firearms/): Three series, each built around a different argument.
- [Prop 65](https://sotarms.com/prop-65/): Information for California customers.
- [Terms of Use](https://sotarms.com/terms-of-use/): The rules for using www.secondoften.com — who the site is for, what you can do with what’s on it, and what happens if something goes wrong.
- [Parts](https://sotarms.com/parts/): The components we fit to our own firearms — measured, marked and checked by us.
- [Upper Receiver Groups](https://sotarms.com/upper-receiver-groups/): Assembled, gauged and checked to the same standard as our complete firearms — ready to drop on your lower.
- [Firearms](https://sotarms.com/firearms/): Five series of complete rifles and pistols, each built to the same documented standard.
- [Agency & Department Sales](https://sotarms.com/agency-department-sales/): Second of Ten sells direct to law enforcement agencies, military units and government purchasers.
- [Gundaddy.com](https://sotarms.com/gundaddy/): Firearms, parts, optics and ammunition. More than 40,000 items in one store.
- [Optics](https://sotarms.com/optics/): Our optics selection is carried by our retail store, Gundaddy.com — and the same people who build our firearms are available to advise on what goes on one.
- [Home](https://sotarms.com/): Second of Ten LLC builds rifle and pistol platforms in Stuart, Florida for private citizens and government agencies.
- [Legal & Privacy](https://sotarms.com/legal-privacy/): A plain-English guide to the rules for using our website and what happens to the information you give us.
- [Lower Receiver Groups](https://sotarms.com/lower-receiver-groups/): The same lower our complete rifles are built on — assembled, function checked and sold complete. Fits any Mil-Spec AR-15 upper.
- [SOTM4A5 Forged Series](https://sotarms.com/firearms/sotm4a5-forged/): HM Defense Monobloc® rifles and short barrel rifles on a forged MOD-0 upper and SOTM4 lower: mid-length gas, HMB™ bolt, A5 recoil.
- [LMT® MRP™ Series](https://sotarms.com/firearms/lmt-mrp-series/): Complete LMT® Monolithic Rail Platform (MRP™) rifles and pistols built by the SOT Custom Shop in 5.56 NATO, 6mm ARC, 6mm MAX and .300 BLK — pairing the MRP™ upper with OE parts that LMT® does not offer together, to the same documented standard as every rifle we make.
- [Index-Marked Bolt Carrier Groups](https://sotarms.com/technical-faqs/index-marked-bcg/): Two marks on one bolt carrier group. Each one makes something invisible checkable.
- [Carrier Completion Kit — Nitride Cam Pin](https://sotarms.com/parts/bolt-carrier-group-parts/carrier-completion-kit-nitride/): The same three parts with a black nitride cam pin — the finish that matches a nitride or phosphate carrier group.
- [Carrier Completion Kit — Full Chrome Cam Pin](https://sotarms.com/parts/bolt-carrier-group-parts/carrier-completion-kit-full-chrome/): Firing pin, retaining pin and a full chrome cam pin carrying the SOT arrow index mark. Five dollars more than the cam pin alone.
- [SOT Nitride Arrow Index Marked Cam Pin](https://sotarms.com/parts/bolt-carrier-group-parts/sot-nitride-arrow-index-marked-cam-pin/): The mark states a direction rather than only a memory: the arrow point faces toward the bolt face, checkable with the bolt out of the rifle.
- [AR15 Firing Pin, Chrome Plated](https://sotarms.com/parts/bolt-carrier-group-parts/ar15-firing-pin-chrome-plated/): 8740 steel, machined to the mil-spec print, precision ground and chrome plated. Buy the spare before you need it.
- [SOT Enhanced Chrome Bolt](https://sotarms.com/parts/bolt-carrier-group-parts/sot-enhanced-chrome-bolt/): Standard geometry — the cam pin passes through a bored hole. C158, shot peened, HPT and MPI, and it ships with the SOT arrow-indexed cam pin and a firing pin.
- [HMB™ Bolt — 6mm ARC, Hard Chrome](https://sotarms.com/parts/bolt-carrier-group-parts/hmb-bolt-6mm-arc-hard-chrome/): The 6mm ARC bolt in hard chrome — the pick for high round counts and suppressed use.
- [HMB™ Bolt — 5.56 / 6mm MAX, Hard Chrome](https://sotarms.com/parts/bolt-carrier-group-parts/hmb-bolt-556-6mm-max-hard-chrome/): Chromed after heat treatment, so the finish sits on a fully hardened bolt. The easier one to wipe carbon off.
- [HMB™ Bolt — 5.56 / 6mm MAX, Black Nitride](https://sotarms.com/parts/bolt-carrier-group-parts/hmb-bolt-556-6mm-max-black-nitride/): The general-duty pick. A surface conversion rather than a plating, so there is no coating to chip at an edge.
- [HMB™ Bolt — 6mm ARC, Black Nitride](https://sotarms.com/parts/bolt-carrier-group-parts/hmb-bolt-6mm-arc-black-nitride/): Cam pin socket in place of a pass-through hole, so material is retained where a drill removes it. The 6.5 Grendel-derived bolt face.
- [SOT Enhanced DLC+ Bolt Carrier Group](https://sotarms.com/parts/bolt-carrier-groups/sot-enhanced-dlc-plus-bcg/): Diamond-like carbon over a high-gloss polished finish, with a chrome-lined bore. Runs as though oiled when dry, and carbon wipes rather than scrubs.
- [SOT Enhanced Super-Stake Bolt Carrier Group](https://sotarms.com/parts/bolt-carrier-groups/sot-enhanced-super-stake-bcg/): The gas key staked by hand, one at a time, on OCKS screws — then checked for mil-spec opening and alignment. The stake is the whole point.
- [SOT Enhanced All-Chrome Bolt Carrier Group](https://sotarms.com/parts/bolt-carrier-groups/sot-enhanced-all-chrome-bcg/): Chrome on every surface — including the extractor and gas key, which most chrome groups leave in phosphate. Nothing on it cleans differently from anything else.
- [SOT Enhanced M16 Chrome Lined Phosphate Bolt Carrier Group](https://sotarms.com/parts/bolt-carrier-groups/sot-enhanced-m16-chrome-lined-phosphate-bcg/): The floor, not the compromise. Built to our own specification, and the only group where both SOT marks are simply how it is made rather than an upgrade.
- [YM 6mm ARC Chrome BCG w/ HMB™](https://sotarms.com/parts/bolt-carrier-groups/ym-6mm-arc-chrome-bcg-hmb/): The same group on the 6mm ARC bolt face, hard chromed after heat treatment with a chrome-lined bolt throat.
- [YM 5.56 M16 Chrome BCG w/ HMB™](https://sotarms.com/parts/bolt-carrier-groups/ym-556-m16-chrome-bcg-hmb/): Made in-house since 1991, with 30% more guide contact area and the HMB™ bolt. Deliberately not staked — and the page explains why.
- [YM 6mm ARC Black Nitride BCG w/ HMB™](https://sotarms.com/parts/bolt-carrier-groups/ym-6mm-arc-black-nitride-bcg-hmb/): The ARC group in nitride, $100 below its chrome twin. Nitride throughout rather than a chrome-lined throat — a real trade, not a finish preference.
- [SOT Enhanced HMB™ 5.56 Bolt Carrier Group](https://sotarms.com/parts/bolt-carrier-groups/sot-enhanced-hmb-556-bcg/): The cam pin socket in place of a pass-through hole, licensed from HM Defense. Material retained where a drill would have removed it.
- [Bolt Carrier Group Parts](https://sotarms.com/parts/bolt-carrier-group-parts/): HMB™ bolts, the SOT Enhanced Chrome Bolt, SOT arrow index marked cam pins, chrome firing pins and carrier completion kits for AR-15 bolt carrier groups.
- [Bolt Carrier Groups](https://sotarms.com/parts/bolt-carrier-groups/): Eight complete AR-15 bolt carrier groups from $109 to $299.95 — HMB™ cam pin socket groups and standard-geometry SOT Enhanced groups, compared by finish, bolt and gas key.
- [DMCA Notice](https://sotarms.com/dmca/): Send Second of Ten a DMCA copyright takedown notice or counter-notice.
- [Agency Sales](https://sotarms.com/technical-faqs/agency-sales/): We build for agencies. We build only for the United States.
- [Who Is HM Defense?](https://sotarms.com/technical-faqs/hm-defense-history/): They didn't come from the gun industry. That turns out to be the whole story.
- [Bore Obstruction Function](https://sotarms.com/technical-faqs/sot816-bore-obstruction/): The piston isolates the action from the barrel. When the barrel spikes, the pressure has somewhere to go — and it is not toward you.
- [MBT-2S vs G2S](https://sotarms.com/technical-faqs/mbt2s-vs-g2s/): Both break at about four and a half pounds. They don't get there the same way.
- [Two-Stage Triggers](https://sotarms.com/technical-faqs/two-stage-triggers/): A total pull you can trust. A break you can time.
- [VC-3 Threadmate](https://sotarms.com/technical-faqs/vc3-threadlocker/): Most thread lockers work by turning into a solid. This one works by refusing to.
- [Castle Nut](https://sotarms.com/technical-faqs/castle-nut-vc3/): A stake is a one-time operation. Your castle nut may not be a one-time job.
- [CN5F + A5](https://sotarms.com/technical-faqs/cn5f-a5-castle-nut/): A longer extension deserves a longer nut.
- [A5 Buffer](https://sotarms.com/technical-faqs/a5-buffer/): Same energy, longer runway, lower peak.
- [Piston vs DI](https://sotarms.com/technical-faqs/piston-vs-di/): The question isn't which system is better. It's where you'd rather put the energy.
- [CAR816 Gas Regulator — Adjusting the Gas](https://sotarms.com/technical-faqs/car816-gas-adjustment/): Clear the rifle. Press the lock. Rotate the regulator to the state that matches what you are shooting. Feel it seat.
- [Pinned Gas Block — Low Profile](https://sotarms.com/technical-faqs/pinned-gas-block-low-profile/): A gas block under a handguard can walk for months before it tells you.
- [Pinned Gas Block](https://sotarms.com/technical-faqs/pinned-gas-block/): The gas block you adjust by hand is the one you least want held on by friction.
- [Plunger Selection — RIFLESPEED](https://sotarms.com/technical-faqs/riflespeed-plunger/): The knob chooses a setting inside a range. The plunger chooses where that range sits.
- [Adjustable Gas — RifleSpeed](https://sotarms.com/technical-faqs/riflespeed-gas/): A fixed gas port is sized for the worst ammunition you will ever feed the rifle.
- [NP3 Bolt Carrier Group](https://sotarms.com/technical-faqs/np3-bcg/): Every other finish we offer answers wear with hardness. This one answers it with lubrication.
- [DLC vs Hard Chrome](https://sotarms.com/technical-faqs/dlc-vs-hard-chrome/): The steel underneath is the same. You're choosing a surface.
- [Polished DLC BCG](https://sotarms.com/technical-faqs/polished-dlc-bcg/): Hard is half of it. Smooth is the other half.
- [Super-Stake BCG](https://sotarms.com/technical-faqs/superstake-bcg/): Every gas key is staked. Very few are staked well.
- [Indexed Gas Key](https://sotarms.com/technical-faqs/indexed-gas-key/): A screw that has begun to turn looks exactly like one that hasn't.
- [Arrow Indexed Cam Pin](https://sotarms.com/technical-faqs/arrow-indexed-cam-pin/): Your cam pin goes back in two ways. Only one of them is the way it came out.
- [6mm MAX vs 6mm ARC Bolt](https://sotarms.com/technical-faqs/6max-vs-6arc-bolt/): Both are 6mm cartridges for an AR-15. Only one of them uses a standard bolt.
- [6mm ARC HMB Bolt](https://sotarms.com/technical-faqs/6arc-hmb-bolt/): A 6mm ARC bolt starts with less steel and more thrust. Then the standard design drills a hole through it.
- [HMB Piston BCG](https://sotarms.com/technical-faqs/hmb-piston-bcg/): The piston hits hardest exactly where the bolt is thinnest.
- [HMB Bolt](https://sotarms.com/technical-faqs/hmb-bolt/): Reinforced where every AR bolt breaks. By not drilling through it.
- [Tension Screw](https://sotarms.com/technical-faqs/tension-screw/): An AR is two halves joined by two pins. Pins in holes need clearance to work.
- [No Forward Assist](https://sotarms.com/technical-faqs/no-forward-assist/): On a precision rifle, forcing a round into the chamber is almost never the right move.
- [Billet Upper Receiver](https://sotarms.com/technical-faqs/billet-upper/): The receiver is the surface everything else on the rifle is measured from.
- [Barrel Bedding](https://sotarms.com/technical-faqs/barrel-bedding/): The barrel doesn't float in the receiver. It's bedded to it.
- [Thermal Fit](https://sotarms.com/technical-faqs/thermal-fit/): No clearance. No compound. Steel held in aluminum.
- [Direct Thread Suppressor Mount](https://sotarms.com/technical-faqs/direct-thread-mount/): Field Answers No. 04: how to mount a suppressor by direct thread, with the advantages and disadvantages. Matching thread and bore, seating on the barrel shoulder, verifying alignment, how tight and how often to check, maintenance, and when a taper or locking mount is the better choice. Bombproof by Design.
- [Hub Locking Mount — HUXWRX HUB-QD](https://sotarms.com/technical-faqs/hub-locking-mount/): Field Answers No. 03: the advantages of a hub locking mount over a taper-only mount, using the HUXWRX HUB-QD Adapter 2.0 as the worked example. How the lock works, installation torque, mounting and removal, trade-offs, and when a plain taper mount is still the right choice. Bombproof by Design.
- [Plan B Suppressor Mount](https://sotarms.com/technical-faqs/planb-suppressor-mount/): Field Answers No. 02: how to install and use a Plan B hub and suppressor mount. Matching the parts, installing the muzzle device and hub mount, verifying alignment, mounting and removing the suppressor, maintenance, and the advantages and trade-offs of a taper mount. Bombproof by Design.
- [VCI Bore Protection](https://sotarms.com/technical-faqs/vci-barrel-protector/): Rust doesn't wait for you to go shooting.
- [Bore Alignment](https://sotarms.com/technical-faqs/bore-alignment/): Every device we install gets checked with a rod.
- [Chrome Lined or Match Bore](https://sotarms.com/technical-faqs/chrome-lined-vs-match-barrel/): One starts more accurate. The other stays where it started.
- [Monobloc Barrel](https://sotarms.com/technical-faqs/monobloc-barrel/): A gas block that can't come loose, because there isn't one.
- [Technical FAQs](https://sotarms.com/technical-faqs/): Searchable answers to technical questions about Second of Ten platforms, components, build standards and suppressor mounting.
- [My account](https://sotarms.com/my-account/)
- [Checkout](https://sotarms.com/checkout/)
- [Cart](https://sotarms.com/cart/)
- [Shop](https://sotarms.com/shop/)
- [Laser Engraving](https://sotarms.com/custom-shop/laser-engraving/): Custom text, logos and markings laser engraved on receivers, handguards, suppressors and accessories. Quoted to the job. Quoted to the job.
- [Feed Ramp Polishing](https://sotarms.com/custom-shop/feed-ramp-polishing/): Rough or coarse feed ramps polished smooth for more consistent feeding. The surface is polished; the geometry is not changed. $45.
- [Gas Block Pinning](https://sotarms.com/custom-shop/gas-block-pinning/): Barrel dimpled for the set screws and the gas block pinned to it — taking one of the most common field failures out of the gas system. $55.
- [Barrel Shortening and Threading](https://sotarms.com/custom-shop/barrel-shortening-and-threading/): Shorten (optional), crown and thread an AR-15 or AR-10 barrel — threads cut concentric to the bore and gauged. Other platforms on request. From $85.
- [Pin and Weld](https://sotarms.com/custom-shop/pin-and-weld/): Permanently attach a muzzle device to bring overall length to 16.0″, or for assault-weapon-law compliance. Removal of an existing pin and weld available. $65.
- [Custom Shop](https://sotarms.com/custom-shop/): SOT Custom Shop services: LMT barrel conversions, pin and weld, barrel shortening and threading, gas block pinning, feed ramp polishing and laser engraving.
- [LMT® MRP™ & MWS Barrel Conversion](https://sotarms.com/custom-shop/lmt-barrel-conversion/): Convert any AR-15 barrel for your LMT MRP ($135) or any AR-10 barrel for your LMT MWS ($175). Any length or caliber, two to three weeks.
- [SOLGW 14.5″ 6mm ARC with RIFLESPEED](https://sotarms.com/parts/barrels/lmt-mrp-barrels/solgw-14-5-6mm-arc-riflespeed/): SOLGW 14.5″ 6mm ARC with RIFLESPEED barrel converted for LMT MRP upper receivers — 6mm ARC, mid-length gas. In stock and shooter ready.
- [Ballistic Advantage 18″ 6mm ARC with RIFLESPEED](https://sotarms.com/parts/barrels/lmt-mrp-barrels/ballistic-advantage-18-6mm-arc-riflespeed/): Ballistic Advantage 18″ 6mm ARC with RIFLESPEED barrel for LMT MRP uppers — 6mm ARC, rifle-length gas, 5/8×24 threads. In stock, shooter ready.
- [SOLGW Precision SPR 18″ 6mm Max® with RIFLESPEED](https://sotarms.com/parts/barrels/lmt-mrp-barrels/solgw-18-6mm-max-riflespeed/): SOLGW Precision SPR 18″ 6mm Max with RIFLESPEED barrel for LMT MRP uppers — 6mm Max, rifle-length gas, 5/8×24 threads. In stock, shooter ready.
- [SOLGW Precision SPR 18″ 6mm Max®](https://sotarms.com/parts/barrels/lmt-mrp-barrels/solgw-18-6mm-max/): SOLGW Precision SPR 18″ 6mm Max barrel converted for LMT MRP upper receivers — 6mm Max, rifle-length gas, 5/8×24 threads. In stock and shooter ready.
- [SOLGW Precision SPR 16″ 6mm Max®](https://sotarms.com/parts/barrels/lmt-mrp-barrels/solgw-16-6mm-max/): SOLGW Precision SPR 16″ 6mm Max barrel converted for LMT MRP upper receivers — 6mm Max, intermediate gas, 5/8×24 threads. In stock and shooter ready.
- [Mos-Tek 10.5″ 6mm Max®](https://sotarms.com/parts/barrels/lmt-mrp-barrels/mos-tek-10-5-6mm-max/): Mos-Tek 10.5″ 6mm Max barrel converted for LMT MRP upper receivers — 6mm Max, carbine gas, 5/8×24 threads. In stock and shooter ready.
- [Government-Contract Clone 10.3″ 5.56 NATO](https://sotarms.com/parts/barrels/lmt-mrp-barrels/govt-contract-clone-10-3-556/): Government-Contract Clone 10.3″ 5.56 NATO barrel converted for LMT MRP upper receivers — 5.56 NATO, carbine gas, 1/2×28 threads. In stock and shooter ready.
- [Monobloc® 16″ 5.56 NATO, Chrome-Lined](https://sotarms.com/parts/barrels/lmt-mrp-barrels/monobloc-16-556-chrome-lined/): Monobloc 16″ 5.56 NATO, Chrome-Lined barrel converted for LMT MRP upper receivers — 5.56 NATO, mid-length gas, 1/2×28 threads. In stock and shooter ready.
- [Monobloc® 16″ 5.56 NATO](https://sotarms.com/parts/barrels/lmt-mrp-barrels/monobloc-16-556/): Monobloc 16″ 5.56 NATO barrel converted for LMT MRP upper receivers — 5.56 NATO, mid-length gas, 1/2×28 threads. In stock and shooter ready.
- [Monobloc® 14.5″ 5.56 NATO, Chrome-Lined](https://sotarms.com/parts/barrels/lmt-mrp-barrels/monobloc-14-5-556-chrome-lined/): Monobloc 14.5″ 5.56 NATO, Chrome-Lined barrel converted for LMT MRP upper receivers — 5.56 NATO, mid-length gas, 1/2×28 threads. In stock and shooter ready.
- [Monobloc® 14.5″ 5.56 NATO](https://sotarms.com/parts/barrels/lmt-mrp-barrels/monobloc-14-5-556/): Monobloc 14.5″ 5.56 NATO barrel converted for LMT MRP upper receivers — 5.56 NATO, mid-length gas, 1/2×28 threads. In stock and shooter ready.
- [Monobloc® 13.9″ 5.56 NATO, Chrome-Lined](https://sotarms.com/parts/barrels/lmt-mrp-barrels/monobloc-13-9-556-chrome-lined/): Monobloc 13.9″ 5.56 NATO, Chrome-Lined barrel converted for LMT MRP upper receivers — 5.56 NATO, mid-length gas, 1/2×28 threads. In stock and shooter ready.
- [Monobloc® 12.5″ 5.56 NATO](https://sotarms.com/parts/barrels/lmt-mrp-barrels/monobloc-12-5-556/): Monobloc 12.5″ 5.56 NATO barrel converted for LMT MRP upper receivers — 5.56 NATO, mid-length gas, 1/2×28 threads. In stock and shooter ready.
- [LMT® MRP™ Compatible Barrels](https://sotarms.com/parts/barrels/lmt-mrp-barrels/): Thirteen barrels converted for LMT MRP uppers — Monobloc® 5.56, a 10.3″ govt clone, 6mm Max® and 6mm ARC. All in stock, shooter ready.
- [AR Trigger Guide](https://sotarms.com/parts/triggers/ar-trigger-guide/): How an AR trigger works, why one fits AR-15 and AR-10 rifles and pistols, single vs two-stage, pull weight by role, curved vs straight bow, and fitting.
- [Barrels](https://sotarms.com/parts/barrels/): The barrels we build our rifles and uppers on, in a wide range of calibers and lengths from 8″ to 24″ — from a roster of nine qualified makers, each chosen for a specific engineering role, and every barrel held to one acceptance standard at our bench.
- [Geissele SSA-E® Super Semi-Automatic Enhanced Trigger](https://sotarms.com/parts/triggers/geissele-ssa-e/): Geissele SSA-E® Super Semi-Automatic Enhanced trigger, 05-160. 0.9–1.3 lb second stage, 2.9–3.8 lb total — our lightest break. AR-15/AR-10, $250.00.
- [Geissele SSA® Super Semi-Automatic Trigger](https://sotarms.com/parts/triggers/geissele-ssa/): Geissele SSA® Super Semi-Automatic two-stage trigger, 05-101. Crane safety certified, laser marked and lot traceable. AR-15/AR-10, $250.00 at Second of Ten.
- [Geissele G2S® Two-Stage Trigger](https://sotarms.com/parts/triggers/geissele-g2s/): Geissele G2S® two-stage AR-15/AR-10 trigger, part 05-145. Wire-EDM sears, 4.25–4.75 lb total pull, curved bow, non-adjustable. $175.00 at Second of Ten.
- [LaRue MBT-2S Two-Stage Trigger — Straight Bow](https://sotarms.com/parts/triggers/larue-mbt-2s-straight-bow/): LaRue MBT-2S straight-bow (flat) two-stage AR-15 trigger, LTMBT-2S-SB. 4.5 lb and 6.0 lb springs included, $139.99 — same price as the curved bow.
- [LaRue MBT-2S Two-Stage Trigger — Curved Bow](https://sotarms.com/parts/triggers/larue-mbt-2s-curved-bow/): LaRue MBT-2S curved-bow two-stage AR-15 trigger (LTMBT-2S). 4.5 lb and 6.0 lb springs included. Our standard fit — $139.99 from Second of Ten.
- [Gas System Components](https://sotarms.com/parts/gas-system-components/): The gas system parts we build our rifles with: RIFLESPEED adjustable Gas Controls and plungers, and low-profile gas blocks, pinned to the barrel the way we pin our own.
- [Triggers](https://sotarms.com/parts/triggers/): Two-stage AR-15 triggers we fit to our own rifles: LaRue MBT-2S in curved or straight bow, Geissele G2S®, SSA® and SSA-E®. Pull weights, specs and prices.
- [Quattro-15 Series](https://sotarms.com/firearms/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.
- [SOTM5 Complete Upper Receivers](https://sotarms.com/upper-receiver-groups/sotm5-complete-upper-receivers/): Large-frame complete uppers on the SOTM5 Billet receiver, for full-power cartridges — .308, 6.5 Creedmoor and 8.6 Blackout.
- [SOTM4 Complete Upper Receivers](https://sotarms.com/upper-receiver-groups/sotm4-complete-upper-receivers/): Choose the barrel. Build the upper. Bombproof by Design™.
- [Custom Shop Series](https://sotarms.com/firearms/custom-shop-series/): Limited editions and one-of-a-kind builds, finished by hand to the same documented standard as every rifle we make.

## Products

- [18″ SOTM5 6.5 Creedmoor PRS Lite Rifle](https://sotarms.com/product/rfl-m5-65cm-b180-blk/): 18″ large-frame 6.5 Creedmoor rifle on Second of Ten’s billet SOTM5 receivers: a thermal-fitted MOD-0 upper over a 7075-T6 lower, Criterion Hybrid barrel, RIFLESPEED adjustable gas pinned to the barrel, Toolcraft double-ejector BCG and Geissele Super Semi-Automatic® (SSA®) trigger. Ships to a licensed FFL dealer for transfer.
- [SOTM4MOD1 A5 Forged Complete Lower Receiver](https://sotarms.com/product/lwr-sotm4mod1a5-f/): The SOTM4MOD1 A5 forged lower from the SOTM4A5 Forged Series rifles, sold complete: Schmid Inside Elite two-stage DLC trigger, Geissele Ambi Posi-Snap selector and Maritime bolt catch, button magazine release, SOT A5 nine-position buffer tube with an A5H2 buffer, and a B5 Systems Bravo stock and Type 23 grip in FDE or black. Fits any Mil-Spec AR-15 upper.
- [12.5″ SOTM4MBA5 Forged Short Barrel Rifle, 11.7″ M-LOK](https://sotarms.com/product/mb-mba5-b125-h117m-blk-s/): The HM Defense Monobloc® short barrel rifle on a forged receiver set: a 12.5″ Monobloc® barrel thermal fitted to SOT's MOD-0 forged upper, on an SOTM4 forged lower. Mid-length gas, SOT Enhanced HMB™ bolt carrier group, A5 recoil system, Schmid Inside Elite two-stage trigger, 11.7″ M-LOK handguard, B5 Systems Bravo furniture, black.
- [16″ SOTM4MBA5 Forged Rifle](https://sotarms.com/product/mb-mba5/): The HM Defense Monobloc® rifle on a forged receiver set: a 16″ Monobloc® barrel thermal fitted to SOT's MOD-0 forged upper, on an SOTM4 forged lower. Mid-length gas, SOT Enhanced HMB™ bolt carrier group, A5 recoil system, Schmid Inside Elite two-stage trigger, B5 Systems Bravo furniture. Choose a 15″ or 13″ M-LOK handguard, FDE or black, or the 13″ Picatinny quad rail in black (FDE coming soon).
- [11.5″ 5.56 NATO Quattro-15 816 Short-Stroke Piston Pistol](https://sotarms.com/product/11-5%e2%80%b3-5-56-nato-quattro-15-816-short-stroke-piston-pistol/): Second of Ten's SOT816E enhanced short-stroke piston upper, a Caracal CAR816 with an HM Defense HMB™ bolt, on Desert Tech's Quattro-15 lower, with a 53-round QMAG-53 and the adapter to run any STANAG magazine. 11.5″ 5.56 NATO, 9.1″ M-LOK handguard, SB Tactical SBA5® brace, B5 Systems Type 23 grip, black anodized.
- [16″ 5.56 NATO Quattro-15 816 Short-Stroke Piston Rifle](https://sotarms.com/product/16%e2%80%b3-5-56-nato-quattro-15-816-short-stroke-piston-rifle/): Second of Ten's SOT816E enhanced short-stroke piston upper, a Caracal CAR816 with an HM Defense HMB™ bolt, on Desert Tech's Quattro-15 lower, with a 53-round QMAG-53 and the adapter to run any STANAG magazine. 16″ 5.56 NATO, 9.1″ M-LOK handguard, VLTOR A5 with CN5F castle nut, B5 Systems furniture, FDE Cerakote® or black anodized.
- [12.5″ 5.56 NATO Quattro-15 Monobloc® A5 Pistol](https://sotarms.com/product/12-5%e2%80%b3-5-56-nato-quattro-15-monobloc-a5-pistol/): An HM Defense Monobloc® upper, thermal fitted to SOT's MOD-0 forged receiver, on Desert Tech's Quattro-15 lower, with a 53-round QMAG-53 and the adapter to run any STANAG magazine. 12.5″ barrel with mid-length gas, 11.7″ M-LOK handguard, VLTOR A5 recoil system, SB Tactical SBA5® brace, black.
- [16″ 5.56 NATO Quattro-15 Monobloc® A5 Rifle](https://sotarms.com/product/16%e2%80%b3-5-56-nato-quattro-15-monobloc-a5-rifle/): An HM Defense Monobloc® upper, thermal fitted to SOT's MOD-0 forged receiver, on Desert Tech's Quattro-15 lower, with a 53-round QMAG-53 and the adapter to run any STANAG magazine. 16″ barrel, chrome-lined or standard bore, 15″ or 13″ M-LOK handguard or 13″ Picatinny quad rail, VLTOR A5 with A5H2 buffer, B5 Systems furniture, black throughout.
- [16″ Quattro-15 Monobloc® RECCE Rifle — Black Anodized](https://sotarms.com/product/16%e2%80%b3-quattro-15-monobloc-recce-rifle-black-anodized/): An HM Defense Monobloc® upper, thermal fitted to SOT's MOD-0 forged receiver, on Desert Tech's Quattro-15 lower, with a 53-round QMAG-53 and the adapter to run any STANAG magazine. 16″ chrome-lined barrel, 15″ M-LOK handguard, black anodized throughout, Reptilia RECC·E™ furniture.
- [16″ Quattro-15 Monobloc® RECCE Rifle — FDE Cerakote®](https://sotarms.com/product/16%e2%80%b3-quattro-15-monobloc-recce-rifle-fde-cerakote/): An HM Defense Monobloc® upper, thermal fitted to SOT's MOD-0 forged receiver, on Desert Tech's Quattro-15 lower, with a 53-round QMAG-53 and the adapter to run any STANAG magazine. 16″ chrome-lined barrel, 15″ M-LOK handguard, finished in FDE Cerakote® throughout, Reptilia RECC·E™ furniture.
- [Carrier Completion Kit — Nitride Cam Pin](https://sotarms.com/product/carrier-completion-kit-nitride/): Three small parts, and the two that get lost. One of them now tells you which way it went in.
- [Carrier Completion Kit — Full Chrome Cam Pin](https://sotarms.com/product/carrier-completion-kit-full-chrome/): Three small parts, and the two that get lost. One of them now tells you which way it went in.
- [SOT Nitride Arrow Index Marked Cam Pin](https://sotarms.com/product/sot-nitride-arrow-index-marked-cam-pin/): The cheapest part in the bolt carrier group. And one of the few that can be installed wrong without telling you.
- [AR15 Firing Pin, Chrome Plated](https://sotarms.com/product/ar15-firing-pin-chrome-plated/): Seven dollars fifty. Which is a strange amount to be one part away from a rifle that does not fire.
- [SOT Enhanced Chrome Bolt](https://sotarms.com/product/sot-enhanced-chrome-bolt/): A bolt, a cam pin and a firing pin. One of them tells you it went back in the right way round.
- [HMB™ Bolt — 6mm ARC, Hard Chrome](https://sotarms.com/product/hmb-bolt-6mm-arc-hard-chrome/): The hole was always the weak point. So it is not a hole any more.
- [HMB™ Bolt — 5.56 / 6mm MAX, Hard Chrome](https://sotarms.com/product/hmb-bolt-556-6mm-max-hard-chrome/): The hole was always the weak point. So it is not a hole any more.
- [HMB™ Bolt — 5.56 / 6mm MAX, Black Nitride](https://sotarms.com/product/hmb-bolt-556-6mm-max-black-nitride/): The hole was always the weak point. So it is not a hole any more.
- [HMB™ Bolt — 6mm ARC, Black Nitride](https://sotarms.com/product/hmb-bolt-6mm-arc-black-nitride/): The hole was always the weak point. So it is not a hole any more.
- [SOT Enhanced DLC+ Bolt Carrier Group](https://sotarms.com/product/sot-enhanced-dlc-plus-bcg/): Carbon has nothing to hold onto. And the marks tell you nothing has moved.
- [SOT Enhanced Super-Stake Bolt Carrier Group](https://sotarms.com/product/sot-enhanced-super-stake-bcg/): The stake is the whole point. So we mark it, and you can see it has not moved.
- [SOT Enhanced All-Chrome Bolt Carrier Group](https://sotarms.com/product/sot-enhanced-all-chrome-bcg/): Chrome all the way through. Including the two parts most groups leave in phosphate.
- [SOT Enhanced M16 Chrome Lined Phosphate Bolt Carrier Group](https://sotarms.com/product/sot-enhanced-m16-chrome-lined-phosphate-bcg/): The one we put our own name on. M16 profile, marked before it ships, and the least expensive group we sell.
- [YM 6mm ARC Chrome BCG w/ HMB™](https://sotarms.com/product/ym-6mm-arc-chrome-bcg-hmb/): Made in-house since 1991. And deliberately not staked — which deserves an explanation, not a footnote.
- [YM 5.56 M16 Chrome BCG w/ HMB™](https://sotarms.com/product/ym-556-m16-chrome-bcg-hmb/): Made in-house since 1991. And deliberately not staked — which deserves an explanation, not a footnote.
- [YM 6mm ARC Black Nitride BCG w/ HMB™](https://sotarms.com/product/ym-6mm-arc-black-nitride-bcg-hmb/): Made in-house since 1991. And deliberately not staked — which deserves an explanation, not a footnote.
- [SOT Enhanced HMB™ 5.56 Bolt Carrier Group](https://sotarms.com/product/sot-enhanced-hmb-556-bcg/): The hole was always the weak point. And now two more things are visible that were not.
- [SOT Custom Shop — Feed Ramp Polishing](https://sotarms.com/product/sot-custom-shop-feed-ramp-polishing/): Custom Shop service. Booked through its request form on sotarms.com; return shipping is charged to your address.
- [SOT Custom Shop — Gas Block Pinning](https://sotarms.com/product/sot-custom-shop-gas-block-pinning/): Custom Shop service. Booked through its request form on sotarms.com; return shipping is charged to your address.
- [SOT Custom Shop — Barrel Shortening and Threading](https://sotarms.com/product/sot-custom-shop-barrel-shortening-and-threading/): Custom Shop service. Booked through its request form on sotarms.com; return shipping is charged to your address.
- [SOT Custom Shop — Pin and Weld](https://sotarms.com/product/sot-custom-shop-pin-and-weld/): Custom Shop service. Booked through its request form on sotarms.com; return shipping is charged to your address.
- [SOT Custom Shop — LMT® MRP™ & MWS Barrel Conversion](https://sotarms.com/product/sot-custom-shop-lmt-mrp-mws-barrel-conversion/): Custom Shop service. Booked through its request form on sotarms.com; return shipping is charged to your address.
- [Geissele SSA-E® Super Semi-Automatic Enhanced Trigger](https://sotarms.com/product/geissele-ssa-e-super-semi-automatic-enhanced-trigger/): Built on the SSA® chassis and retuned lighter: 0.9–1.3 lb on the second stage, the lightest break we offer. Same price as the SSA® — so the choice is about the rifle, not the budget.
- [Geissele SSA® Super Semi-Automatic Trigger](https://sotarms.com/product/geissele-ssa-super-semi-automatic-trigger/): The Super Semi-Automatic®: the semi-automatic version of Geissele's Super Select-Fire®. It publishes the same pull weights as the G2S® — what the difference buys is the record behind each part.
- [Geissele G2S® Two-Stage Trigger](https://sotarms.com/product/geissele-g2s-two-stage-trigger/): Geissele's two-stage at its most direct: the same tool steel and wire-EDM-cut sears as the SSA®, with three things left out — and Geissele lists all three.
- [LaRue MBT-2S Two-Stage Trigger — Straight Bow](https://sotarms.com/product/larue-mbt-2s-two-stage-trigger-straight-bow/): The same LaRue MBT-2S with a straight bow. A flat face gives the finger one repeatable contact point — at the same price as the curved bow.
- [LaRue MBT-2S Two-Stage Trigger — Curved Bow](https://sotarms.com/product/larue-mbt-2s-two-stage-trigger-curved-bow/): Our standard fit and the best value in the range. A two-stage trigger with the take-up built in as a warning — and both springs in the box, so the weight is chosen for the rifle, not the catalog.
- [SOTM4 16″ Monobloc® 5.56 NATO, No Forward Assist, 13″ M-LOK Handguard](https://sotarms.com/product/sotm4-16%e2%80%b3-monobloc-5-56-nato-no-forward-assist-13%e2%80%b3-m-lok-handguard/): 16″ HM Defense Monobloc® barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, on the SOT Standard forged 7075-T6 upper with no forward assist. 13″ SOT Wedge-Lock M-LOK handguard and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 16″ Monobloc® Slim Line 5.56 NATO, No Forward Assist, 14″ M-LOK Handguard](https://sotarms.com/product/sotm4-16%e2%80%b3-monobloc-slim-line-5-56-nato-no-forward-assist-14%e2%80%b3-m-lok-handguard/): Slim Line: 4 lb 0.5 oz. 16″ HM Defense Monobloc® barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, on the SOT Standard forged 7075-T6 upper with no forward assist. 14″ Midwest Industries Slim Line M-LOK handguard and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 16″ Monobloc® 5.56 NATO, 13″ Quad Rail Handguard](https://sotarms.com/product/sotm4-16%e2%80%b3-monobloc-5-56-nato-13%e2%80%b3-quad-rail-handguard/): 16″ HM Defense Monobloc® barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper. 13″ SOT Wedge-Lock quad rail handguard and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 16″ Monobloc® 5.56 NATO, 13″ FDE Anodized M-LOK Handguard](https://sotarms.com/product/sotm4-16%e2%80%b3-monobloc-5-56-nato-13%e2%80%b3-fde-anodized-m-lok-handguard/): 16″ HM Defense Monobloc® barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper. 13″ SOT Wedge-Lock M-LOK handguard in FDE anodized finish and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 16″ Monobloc® 5.56 NATO, 15″ FDE Anodized M-LOK Handguard](https://sotarms.com/product/sotm4-16%e2%80%b3-monobloc-5-56-nato-15%e2%80%b3-fde-anodized-m-lok-handguard/): 16″ HM Defense Monobloc® barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper. 15″ SOT Wedge-Lock M-LOK handguard in FDE anodized finish and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 16″ Monobloc® (Chrome-Lined) 5.56 NATO, 13″ M-LOK Handguard](https://sotarms.com/product/sotm4-16%e2%80%b3-monobloc-chrome-lined-5-56-nato-13%e2%80%b3-m-lok-handguard/): 16″ HM Defense Monobloc® chrome-lined barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper. 13″ SOT Wedge-Lock M-LOK handguard and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 16″ Monobloc® 5.56 NATO, 13″ M-LOK Handguard](https://sotarms.com/product/sotm4-16%e2%80%b3-monobloc-5-56-nato-13%e2%80%b3-m-lok-handguard/): 16″ HM Defense Monobloc® barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper. 13″ SOT Wedge-Lock M-LOK handguard and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 14.5″ Monobloc® (Chrome-Lined) 5.56 NATO, 13″ FDE Anodized M-LOK Handguard](https://sotarms.com/product/sotm4-14-5%e2%80%b3-monobloc-chrome-lined-5-56-nato-13%e2%80%b3-fde-anodized-m-lok-handguard/): 14.5″ HM Defense Monobloc® chrome-lined Black Phosphate barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper. 13″ SOT Wedge-Lock M-LOK handguard in FDE anodized finish and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 14.5″ Monobloc® (Chrome-Lined) 5.56 NATO, 13″ M-LOK Handguard](https://sotarms.com/product/sotm4-14-5%e2%80%b3-monobloc-chrome-lined-5-56-nato-13%e2%80%b3-m-lok-handguard/): 14.5″ HM Defense Monobloc® chrome-lined barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper. 13″ SOT Wedge-Lock M-LOK handguard and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 14.5″ Monobloc® 5.56 NATO, 13″ M-LOK Handguard](https://sotarms.com/product/sotm4-14-5%e2%80%b3-monobloc-5-56-nato-13%e2%80%b3-m-lok-handguard/): 14.5″ HM Defense Monobloc® barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper. 13″ SOT Wedge-Lock M-LOK handguard and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 13.9″ Monobloc® (Chrome-Lined) 5.56 NATO, 11.7″ M-LOK Handguard](https://sotarms.com/product/sotm4-13-9%e2%80%b3-monobloc-chrome-lined-5-56-nato-11-7%e2%80%b3-m-lok-handguard/): 13.9″ HM Defense Monobloc® chrome-lined barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper. 11.7″ SOT Wedge-Lock M-LOK handguard and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 13.9″ Monobloc® (Chrome-Lined) 5.56 NATO, 13″ M-LOK Handguard](https://sotarms.com/product/sotm4-13-9%e2%80%b3-monobloc-chrome-lined-5-56-nato-13%e2%80%b3-m-lok-handguard/): 13.9″ HM Defense Monobloc® chrome-lined barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper. 13″ SOT Wedge-Lock M-LOK handguard and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.
- [SOTM4 12.5″ Monobloc® 5.56 NATO, 11.7″ M-LOK Handguard](https://sotarms.com/product/sotm4-12-5%e2%80%b3-monobloc-5-56-nato-11-7%e2%80%b3-m-lok-handguard/): 12.5″ HM Defense Monobloc® barrel, 5.56 NATO / .223, 1:8 twist, mid-length gas, thermal fitted to the SOTM4 MOD-0 forged 7075-T6 upper. 11.7″ SOT Wedge-Lock M-LOK handguard and SOT Enhanced HMB™ Black Nitride BCG and Breek Arms WARHAMMER Mod2 ambi charging handle included. Ships direct, not a firearm.


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