Words and Pics: Alex Dai


This is certainly my favorite AR build so far. It all started with a Geissele MK4 Federal OD Green rail and it took me about three months to get it all set. My FBI HRT/SWAT rifle build is based on a GBLS DAS GDR15 CQB version.

Why FBI HRT/SWAT rifle?

I didn’t know I had a thing for ODG until I saw the pics of FBI HRT/SWAT rifle with a Geissele MK4 Federal ODG rail. That ODG rail combines with black receivers is irresistible to me. After a long wait, I finally sourced one of these rare ODG rails to replace my old black MK8 for the new build.

To be clear, this is not a faithful FBI rifle clone. According to the parts list and reference pics, it seems to me the most iconic symbols for an FBI HRT/SWAT rifle are the Geissele MK4 federal ODG rail, 11.5” barrel, and CTR stock. Therefore, I kept these three parts and chose other parts based on my specific needs and preferences.


I bought my first GBLS GDR15 last summer, and it never let me down. My first GBLS build was a 14.5” URG-I which also took me forever to get done, but that is another story. This FBI clone is my second GBLS build, so you know I do love this platform.

The GBLS DAS is built like a tank, the whole design feels solid and reliable. The functional BCG makes crisper recoil than any EBBs, but possibly not kicking as hard as some GBBRs. What is most beyond my expectations is the range and accuracy. It shoots as accurately and with the same range as my PTW, if not better.

However, as the GBLS receivers are not designed in a 1:1 scale to the real steel ones, you might not be able to use a variety of real steel parts on your replica. This is one of the biggest drawbacks of this system for me. Besides, I expect GBLS to release a lighter trigger and a blank receiver version in the future.

All in all, if you’re looking for a platform that combines GBBR functionality with AEG reliability, the GBLS DAS is a no brainer.

My FBI build is based on a GDR15 CQB version which came with a 10.5” outer barrel, so I had to add a 1” barrel extension to get an 11.5” outer barrel.

As GBLS upper won’t fit a real steel barrel nut, I ordered an AEG spec Geissele type barrel nut form GBLSUSA.

GBLSUSA also helped me to replace the stock trigger with their Geissele style flat trigger. Even though the flat trigger looks cool and feels excellent, it won’t significantly reduce the trigger pull weight.

ODG Parts

Geissele MK4 Federal Rail 10”

I always prefer the boxy look of the MK4/MK8 rail than the slimmer profile of the MK14/MK16 rail. With the integrated picatinny rail sections at the fore of the rail in the 3, 6 and 9 o’clock positions, the MK4 is even more versatile and modular than the MK8. And the federal version is 10” instead of 9.5” which is perfect length for an 11.5” SBR. Like any Geissele SMR rails, the MK4 Federal also bundled with a Geissele Super Gas block.

This PTS x Magpul MIAD AEG Grip has been discontinued for a while, so it took me some time to find one. Fortunately, I successfully modified it to fit the GBLS.

Magpul CTR Stock with Bruno’s 3D print battery pad

Magpul Original Mag Assist

Radian Raptor Ambidextrous Charging Handle

Cloud Defensive LCS (Light Control System) with Surefire ST-07

I chose the LCS not only because they offer in ODG, but mostly because it gives me the ability to hard-mount a Surefire switch to the rail while controlling loose cable as well.

TangoDown IO Cover For Aimpoint T-2

True North Concepts GripStop–K M-LOK

The GripStop is lightweight and streamlined, and its unique design allows me to pull the firearm rearward and maintain a solid purchase on the rail with the support hand.

I have tried to add as many ODG parts as possible on this FBI HRT build, but I would not call it perfection, unless I get an anodized ODG buffer tube and mod it to fit GBLS. Nevertheless, I am still satisfied with the current configuration.

Other Parts

Unity Tactical FAST Mount

Somebody may think the Unity Tactical Fast Mount is too high (2.26”), but it’s only 1/3″ higher than other popular 1.93” mounts, and that increased height makes it work great with NVG’s, gas masks, and heads up shooting techniques. Also, the built-in front and rear sight eliminates the need for separate BUIS, saving weight and space. For me, this is by far the best option to mount an Aimpoint T2.

PTS 51T Flash Hider and MK18 Suppressor

I always love the aggressive look of the AAC Blackout 51T Flash Hider, and the PTS one is a faithful replica. The PTS MK18 suppressor holds my tracer unit perfectly, which is a bonus for indoor games.

Steiner DBAL-A3

I don’t usually use any laser/IR device in airsoft games, so this DBAL-A3 is just for the look. And considering it is a fairly pricy device, I tend to replace it with a DBAL-A2 replica for gaming.

I have played with this FBI HRT/SWAT build for several games, and it felt exactly how I expected. Sometimes I would adjust the setup to meet different needs, like adding a magnifier to be more versatile, and changing to a crane stock for a larger battery.

Next, I want to swap both my GBLS builds to blank receivers with realistic marking, and maybe buy the new released steel heavy weight BCG.

Parts List



• Flat Trigger

• G-style Barrel Nut

Airsoft Parts

• 1” Outer Barrel Extension

• PTS 51T Flash Hider

• PTS MK18 suppressor

• PTS x Magpul AEG Trigger Guard

• PTS x Magpul MIAD AEG Grip (ODG)

• Strike Industries Style AR15 Ultimate Dust Cover

Real Steel Parts

• Geissele MK4 Federal Rail 10” (ODG)

• Geissele Super Gas Block

• Magpul CTR Stock (ODG)

• Magpul Original Mag Assist (ODG)

• Radian Raptor Ambidextrous Charging Handle (ODG)

• Cloud Defensive LCS (ODG) with Surefire ST07 Tape Switch

• TangoDown IO Cover For Aimpoint T-2 (ODG)

• True North Concepts GripStop–K for M-LOK (ODG)

• Aimpoint T2

• Unity Tactical FAST Mount

• Surefire M300 Mini Scout Light with DS00 Dual Switch Assembly

• Arisaka Offset Scout Mount Picatinny

• Steiner DBAL-A3

• Ferro Concepts Slingster (Ranger Green)

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