FBI Regional SWAT clone build: Colt 11.5 and green Mk4 Federal rail

In October 2015 the FBI ordered 2,500 Colt 11.5 inch Commando barrels with no front sight post, then thousands of Geissele rails. Posters who say they carry these guns describe an 11.5 inch Colt under an OD green Geissele Mk4 Federal rail on field office SWAT carbines. Collectors call it the FBI Regional SWAT carbine.

We rebuilt it from purchase records, maker pages and the AR15.COM clone thread, then matched every part to our catalog on 27 September 2026. You'll see what's documented, what's only reported and what you can buy.

What an FBI Regional SWAT clone copies

An FBI Regional SWAT clone copies a Colt pattern carbine with an 11.5 inch barrel, carbine gas and Geissele's 10 inch Mk4 Federal rail in OD green. The setup dates from about 2015.

Geissele says that rail filled FBI contracts. Green as the SWAT color rests on forum reports and photos, not a document.

What rifle does FBI SWAT use?

FBI SWAT uses Colt pattern M4 carbines. A retired FBI firearms instructor wrote in 2013 that field SWAT mostly carried select fire Colt M4s. Recent forum posts still describe an 11.5 inch Colt pattern gun.

The program began in 1973, after Wounded Knee, with five agent teams in six field offices.

Regional SWAT is a collector's name, not the FBI's

The FBI doesn't say regional. Its SWAT at 50 story says field office SWAT and never uses the word. A poster claiming FBI experience wrote in 2023 that the term isn't used.

A 2010 FBI Atlanta page called Atlanta one of nine Enhanced SWAT teams prepared to augment the full time Hostage Rescue Team. We found no newer count. Members serve on collateral duty and certify through a three week Quantico course.

FBI Atlanta agents beside a Lenco armored truck in Brunswick, Georgia, on 4 February 2026, during an FBI and DEA operation against a Glynn County drug trafficking organization. We can't identify the suppressed carbine's rail or optic, or tell whether these agents are on the SWAT team. Photo: courtesy FBI Field Offices, via DVIDS. Public domain, via Wikimedia Commons.

HRT, SWAT, agent or vehicle unit: which FBI carbine is which

According to posters who say they carry or issue these guns, the rail color tells you which FBI program paid for a carbine.

Why an FBI HRT clone is a different build

Posters tie HRT uppers to Colt's heavy 11.5 inch barrel, sold by Colt Parts as SP402251, and to Spuhr mounts. They split on its rail color: tan, DDC or, per a 2023 poster, almost all black.

Orders funded by the FBI's CIRG division for Geissele 6ARC rifles in 2025 and 2026, plus rifle parts for HRT, suggest HRT is moving to Geissele built rifles. If you want an HRT gun, you're building a different list.

FBI SWAT clone parts list: the issued part and what to buy

Here's the whole carbine on one screen. We started from an archived enthusiast parts list and tested each line against the records. A poster claiming FBI experience says SWAT guns vary by office and operator, so no single list is correct.

Every part shown is listed on GPP. The Colt lower, Colt barrel, green rail and Geissele Government handle had no offer in stock on 27 September 2026. Product photography is supplied by the listed merchants through their affiliate feeds.

Strong means records or a maker's page, moderate means repeated owner reports, weak means a post or two. Exact means we list the issued or same standard part.

The lower receiver group

The lower is where your clone parts ways with the issued gun.

Lower receiver: Colt M4 pattern, semi auto only

No record gives the SWAT lower's model. A 2013 account says field SWAT carried Colt M4s capable of full auto, and forum posters have since reported M4A1 marked lowers on SWAT guns. They disagree on how many are still select fire.

One owner's issued agent and vehicle unit lowers look like commercial Colt LE6920s, with LE and CR serial prefixes.

Yours has to be semi auto. Colt's LE prefix M4 Commando lower is our equivalent card, with no offer in stock. PSA's M4 Carbine lower is the budget look.

Trigger and trigger guard: Colt GI or Geissele SSA

The FBI bought Geissele select fire triggers, SSFs among them, from 2008 to 2016 and SSA semi auto triggers in 2015. A 2017 order bought Geissele semiautomatic triggers "in support of SWAT program" without naming the model. A poster claiming FBI experience says operators choose between the select fire group and an SSA.

The SSA is documented, so it's our exact card. The enthusiast parts list names the SSA-E, but we found no FBI order for it. CMMG's kit stands in for the Colt group.

Posters describe a standard mil spec trigger guard.

Stock and rear sling mount: Magpul CTR, green or black

FBI orders named the mil spec Magpul CTR in 2013, 2014 and 2017, the last as MAG310BLK, black. No order names OD green, but posters and the enthusiast parts list put green CTRs on SWAT guns. Buy the mil spec MAG310 in either color, since the commercial MAG311 won't fit a mil spec tube.

No record names the buffer. Posters report an H buffer with a standard spring, and an H2 in one issued gray gun. The CQD rear sling mount on the enthusiast parts list appears nowhere else we looked, and we don't list one.

Grip: Ergo SureGrip, A2 or Hogue

The FBI bought black Ergo 4009 grips, the Original ERGO Grip AT SureGrip, in lots of 1,200 and 1,250 in 2015, naming no program. Posters saw black Ergos on SWAT guns in 2018 and 2022 and say earlier guns had Hogues. Black only is disputed, since one issued gray gun wore a graphite gray Ergo.

Our Ergo card is 4009-BK, though the listing says Ambidextrous SureGrip. The Hogue card covers the earlier guns.

The upper receiver group

Most of your upper is Colt, and most Colt parts were out of stock.

Upper receiver: Colt M4 flat top

Posters say most uppers they've seen are Colt marked, and the FBI's Colt parts contracts don't itemize them. We found nothing tying the keyhole, square or cage code marks on the enthusiast parts list to FBI guns, so any Colt M4 flat top will do.

None of our 11.5 inch or stripped Colt upper listings had stock, so Expo's T marked upper is your budget stand in.

Barrel: Colt 11.5 inch LE6933 profile, 1 in 7

The barrel has a clear paper trail. The FBI's October 2015 order bought 2,500 Colt 11.5 inch Commando barrels, 1 in 7, with no front sight post and a .074 inch gas port. It gives no profile or program.

Builders use Colt's LE6933 barrel, 401065 stripped, which Brownells lists as chrome lined with carbine gas. Watch the label: Colt Parts sells SP401065 as an FBI HRT Profile assembly, and we haven't confirmed the profile with Colt. Ports vary too, from .074 on that order to .073 on a 2014 one and .070 in two posts.

The Colt card was out of stock. Daniel Defense's 11.5 inch government barrel is your in stock equivalent. The Commando name also sits on the Colt 733 Commando from Heat.

Gas block: Geissele Super Gas Block on carbine gas

No record names the gas block. Posters and the enthusiast parts list describe a Geissele Super Gas Block held by set screws, stainless on issued guns.

Geissele now sells it as the Super Compact Gas Block, 05-807B, in black, made from 17-4 stainless for a .750 inch journal, with no bare stainless version listed. BCM's tube covers the carbine gas system and LBE's block is the budget pick.

Muzzle and suppressor: A2 hider, then HUXWRX Flow 556K

For the classic gun, fit an A2 birdcage. Posters call the A2 standard from 2018 to 2021, and a 2019 post said field SWAT had no cans.

Since September 2021 the FBI has bought suppressors, muzzle devices and training aids from OSS, later HUXWRX, including 5.56 cans with flash hiders in 2023. Posters in 2022 and 2023 put OSS or HUXWRX cans on QD hiders on field SWAT guns and name the Flow 556K. Which teams got cans isn't documented.

Our Flow 556K card comes with the standard 1/2x28 QD hider, since no source names the FBI's.

For other cans and short suppressed setups, see our best 5.56 suppressors and the Sicario task force build.

Bolt carrier and charging handle: GI or Geissele Government

A poster claiming FBI experience lists a standard government type carrier with no maker. The Colt M16 carrier card is that pattern, out of stock, and BCM's is the in stock equivalent.

Geissele says its Government Charging Handle, 05-851, was developed for FBI special agents. Posters report black ones on some Enhanced team rifles in 2020 and on every regional gun at a 2022 event. LBE's card stands in for the earlier Colt handle. We found nothing supporting the PRI Gas Buster on the enthusiast parts list. Our AR-15 charging handle guide covers the alternatives.

The Geissele Mk4 Federal rail in OD green

The rail makes your gun read as FBI, and it's the hardest part to buy in green.

Handguard: 10 inch Mk4 Federal, part 05-430ODG

Geissele's page for the 10 inch Mk4 M-LOK, SKU 05-430, says it's the same rail used to fill FBI contracts. Gen 2 rails, with a longer bottom Picatinny section than Gen 1, showed up on regional guns in 2022.

The FBI bought 1,350 Super Rails in February 2017 and 1,725 that December, with no length, color or program stated. That's far more than the roughly 1,100 SWAT members GAO counted, so many likely went to agent guns.

The black card is the same rail in another program's color, and it was in stock.

SOCOM's Geissele railed carbine gets its own M4A1 URGI clone build.

Where a green Federal rail still turns up

Geissele's customer service account wrote in November 2018 that the Federal rails offered over Black Friday were contract overruns. Green ones turned up again in later blem sales and a 2023 listing.

Geissele's site now lists the 10 inch Mk4 only in black and DDC. Our green card's three offers were all out of stock, so your best bet is a Geissele sale.

Optic and mount: Aimpoint T-2, H-2 or Romeo4M

The mount is documented. The optic on a SWAT gun is disputed, so you get both sides.

Which Aimpoint SWAT guns carry is disputed

The records favor the H-2. The FBI bought Aimpoint Micro H-2s with Daniel Defense mounts in sets of 640, 33 and 1,750 in 2015 and 2016. No order names a program, and 2,423 sets is more than twice the SWAT headcount.

The forum favors the T-1 and T-2. A poster claiming FBI experience wrote in 2020 that SWAT guns get the T-1, T-2 or SIG Romeo4M and agent guns the H-1, H-2 or Romeo4M. Against that, posters read a 2023 photo of field office SWAT members as showing H-2s.

We card the T-2 for your SWAT clone. The T-1 is discontinued. The H-2 fits an agent gun and maybe some SWAT guns, but it has no night vision settings. Our Romeo4M listing had no offer in stock, so it has no card.

Mount: Daniel Defense 03-045-18025, no spacer

Daniel Defense's Aimpoint Micro Mount, 03-045-18025, appears in all three H-2 orders, and the 1,750 set order specifies no spacer. Posters say regional guns run DD mounts, with SIG mounts under Romeos. You could buy it in stock at $105.80.

Sights, light, laser, foregrip and sling

These parts vary most from gun to gun, so you're picking the common choice.

Rear and front sight: Troy folding BattleSights

The FBI bought Troy front battle sights in May 2019. A poster claiming FBI experience called Troy sights standard in 2018 and said in 2020 that new guns get Magpul MBUS Pros, which a 2022 observer saw on every regional gun at one event. Both Troy cards were in stock.

Light: SureFire Mini Scout or Inforce WML

Three forum accounts from 2020 to 2023 put SureFire Mini Scouts on SWAT guns and Inforce WMLs on agent guns, though the enthusiast parts list puts the Inforce first. The FBI bought Inforce lights at agent scale, 1,200 in 2015 and 1,500 in 2017.

Nobody names the Mini Scout model, so our first card is SureFire's current M340C. If you're copying an agent gun, the Gen 3 Inforce stands in for the out of production Gen 2.

Laser: tan PEQ-15, or the civilian ATPIAL-C

FBI records name the AN/PEQ-15 as ATP-000-A18 and the black ATP-000-A22, and 2014 and 2016 orders list tan units. Posters call tan PEQ-15s standard on SWAT guns.

The full power PEQ-15 is law enforcement only, so both cards are civilian equivalents. Only Steiner's black DBAL-A3 was in stock. Our civilian IR laser guide covers the rest, and the M4A1 Block II clone build hits the same problem.

Foregrips and sling: OD green AFG, wide two point

No FBI order for AFGs turned up, but posters and the enthusiast parts list put OD green Magpul AFGs on SWAT guns. The M-LOK AFG is an equivalent that bolts to the rail slots.

A May 2015 order lists "TY Viking Tac wide sling, black", and posters call VTAC slings basic issue but not universal. We read that as the black VTAC MK2 Wide Padded, which is our inference, not the order's wording.

FBI SWAT carbine variants over its service life

The green rail gun is the latest of several FBI SWAT long guns.

From the MP5/10 to quad rail Colt M4s

The FBI adopted the MP5/10A2 in 1994, and its 2008 equipment page still listed a 10mm MP5 as the primary weapon, next to a Springfield .45. Our guide to the FBI Glock 19M and its size siblings covers today's pistols.

After FBI ballistic testing showed .223 penetrating less than its submachine gun loads, M16s and M4s took over. American Rifleman puts the Rock River M4s chosen in 2004 with investigative agents, not SWAT.

Early Colt SWAT guns wore quad or drop in rails with EOTechs, then Troy free float rails.

Detroit FBI SWAT members take cover on a pier during a maritime training exercise with the Coast Guard Cutter Bristol Bay in Detroit, 17 October 2013. Their carbines carry quad rails and EOTech sights, the earlier setup. Photo: Petty Officer 3rd Class George Uhl, U.S. Coast Guard. Public domain, via Wikimedia Commons.

A Milwaukee FBI SWAT member on the urban assault course at Fort McCoy, Wisconsin, 27 April 2016. His carbine has a free float rail with round lightening holes, an EOTech sight and a weapon light, the look before the Geissele rails. Photo: Jamal Wilson, Fort McCoy Multimedia Visual Information Branch, U.S. Army. Public domain, via Wikimedia Commons.

The civilian legal path to an FBI SWAT clone

Your clone meets federal law at the barrel, the select fire parts and the can.

SBR or pistol: the two ways to keep 11.5 inches

An 11.5 inch barrel on a receiver with a stock is a short barreled rifle under the NFA. ATF announced on October 9, 2026 that it would stop enforcing NFA approval and registration for SBRs, though it still accepts a Form 1 or Form 4 at $0. That's a policy that can be reversed, and some states ban SBRs or only allow registered ones.

As a pistol with no stock it isn't an SBR, but brace rules keep changing, so read our AR-15 pistol brace rules first. Our NFA paperwork in 2026 guide covers the forms and the October 9 change, which also apply to the Mk18 Mod 0 clone build and CQBR Block II clone build.

Keeping 16 inches: a pinned 14.5 or a Colt 16.1

A 14.5 inch barrel with a device pinned and welded to reach 16 inches isn't an SBR, because a permanently attached device counts and a removable one doesn't. A 16 inch barrel works too, with more barrel past the 10 inch rail.

We found no Colt pinned 14.5 in our catalog, so Colt's 16.1 inch LE6920 parts are your equivalents.

Select fire parts, suppressors and LE only lasers

The auto sear and select fire group are machine gun parts, so your clone stays semi auto. ATF's October 9 change covers suppressors too, and our guide to what changed for suppressors covers the tax side.

The PEQ-15 limit is the maker's sales restriction, not an NFA rule. State laws on SBRs, suppressors and rifle features vary, so check yours.

What you can buy today and what is unobtainable

We matched 23 part slots against our catalog on 27 September 2026. The issued or same standard part is listed for 20, but five of those had no stock.

Green rail, Colt barrel and Geissele handle: out of stock

On 27 September our listings for the green Federal rail, Colt's LE6933 barrels and 11.5 inch uppers, the Colt carrier, the Geissele Government handle, Colt's LE prefix lower, the ATPIAL-C and the discontinued T-1 had no offer in stock. Neither did our Romeo4M listing.

Parts no retailer can sell you

No retailer in our feeds can sell you the select fire lower or auto group, both machine gun parts, or the law enforcement only PEQ-15 and LA-5 lasers. Our feeds carry neither the 2014 Superior Tooling contract barrels nor Troy's 9 inch TRX Extreme rail, and the .067 inch FBI gas block has no record at all.

Colt 6933 SBR and pistol: a factory head start

Colt's LE6933-OEM2 is an 11.5 inch SBR sold, per its listing, without stock, handguard, trigger guard or gas block, ready for the Geissele parts. It was $987 from a dealer. The M4P6933 pistol with an SBA5 brace was $1,276.17. Both are equivalents.

Add a black Federal rail at $383.99, the Super Gas Block at $67.99, a green CTR at $49.99 and a CMMG trigger guard at $7.36 to the SBR, and you're at $1,496.33. With a T-2 and the DD mount it's $2,525.13. We found nothing tying Colt's LE6920-FBP Federal Patrol to the FBI.

FBI SWAT builds on GPP: what they show

We went looking for FBI clones in our own build data.

No GPP builder saved a build under this name from 10 December 2025 to 27 September 2026. We searched every cart name in that window and every public build.

Federal rail demand is real, but it isn't green. From 31 January to 27 September 2026, our users added a 10 inch Mk4 Federal rail 44 times from 26 sessions, and only 2 adds were OD green.

One guest cart from 13 September 2026 comes close: green rail, Colt upper, Colt carrier and OD green AFG, with no lower or barrel yet. Nobody has searched GPP for FBI or SWAT since our search log began on 23 April 2026. Session tracking started in mid April, so we can't bot check earlier adds.

What the internet gets wrong about the FBI SWAT carbine

Several FBI clone myths trace to one post or one label. Here's our correction list, then the four that matter most for your build.

The green Federal rail is a SWAT rail, not HRT

The HRT name sits in the title of an AR15.COM industry thread, MK4 HRT FBI rail OD green. In that thread a 2018 poster put green rails on division SWAT guns and had never seen one on an HRT gun.

The HRT heavy barrel does not belong on a green rail gun

Builders pair the green rail with the LE6933 profile and treat Colt's heavy 11.5 inch, SP402251, as HRT. Colt Parts labels SP401065, the LE6933 number, as FBI HRT Profile, and that label still caught a 2026 builder. Go by the part number.

No FBI only gas block with a .067 inch port

The claim traces to one pseudonymous 2018 post giving .067 inch for the FBI, and no record names the block. A poster who photographed a block shipped to Quantico with a Gen 1 Federal rail found it identical to a commercial one. The 2015 barrel order specifies a .074 port.

The Quantico Special is not the SWAT rifle

Geissele's Quantico Special is a 16 inch rifle with a 13.5 inch Mk4 rail. Geissele says it's approved for individual federal agents to own personally. The SWAT carbine you're copying is an 11.5 inch Colt.

Sources and photo credits

The AR15.COM thread is your best photo reference.