Build template

Block 2 IAR

Sustained fire from a magazine-fed AR-15

Custom AR-15 (Build From Scratch)9 componentsCurrent build cost: $3,795.83Prices as of Jul 1, 2026

The Block 2 IAR is a civilian infantry automatic rifle built on the SOCOM Block 2 M4 layout, aimed at the advanced shooter who wants high-volume, fast follow-up fire from a magazine-fed AR-15. It pairs a Daniel Defense M4A1 upper and full-auto-profile bolt carrier with a Partisan Disruptor forced reset trigger, an EOTech EXPS3 holographic sight backed by a G33 magnifier, and a Magpul D-60 drum for sustained strings.

This is a range and outdoor-defense rifle first: the quad-rail upper adds thermal mass around the barrel, the 1x holographic window drives close-quarters speed, and the flip-in 3x magnifier extends positive identification past 200 yards. It is not a subtle build, and the drum plus holographic combo pushes the weight up, but that is the trade for the sustained-fire handling and capacity it targets.

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Host platform

Custom AR-15 (Build From Scratch)

Parts build: the receivers and barrel are line items in the list below, so there is no complete rifle to buy first.

Why this build

The reason this combination works is the optic. An EXPS3 with the 68 MOA ring and 1 MOA center dot is the fastest way to put rounds on a close target with both eyes open, and the G33 flips into the optical path behind it for a true 3x view when you need to read a target at distance. Running a holographic sight and a dedicated magnifier beats a fixed LPVO for a sustained-fire role because you keep true 1x speed and only add magnification when the situation calls for it.

The Partisan Disruptor is a forced reset trigger, not a binary or a full-auto part. Its bolt-carrier-driven reset lets a disciplined shooter run strings far faster than a standard trigger while each pull still fires one round. The Daniel Defense M16-profile bolt carrier gives the extra reciprocating mass that keeps a gas gun cycling reliably through those fast strings, and the quad-rail upper's steel and aluminum act as a passive heat sink when the barrel warms up.

The rest of the parts are chosen for hard use rather than weight savings. The B5 Enhanced SOPMOD stock gives a wide, repeatable cheek weld under the raised holographic sight, the Radian Raptor-LT charging handle lets you clear or check the chamber ambidextrously with the optic sitting close over the receiver, and the D-60 drum keeps 60 rounds ready so the FRT's rate of fire is not throttled by 30-round reloads.

Parts list

Complete Uppers

Daniel Defense M4A1 FSP Upper Receiver Group 14.5"

$1,551.00 at Optics Planet · Out of stock

The Daniel Defense M4A1 FSP upper is the classic Block 2 foundation: a 14.5-inch cold hammer forged barrel with a Surefire SF3P pinned and welded to a permanent 16-inch barrel length, carbine gas, a pinned front sight post, and a full quad rail. The quad rail is the point here; its mass helps soak up heat during sustained fire, and the four Picatinny faces mount anything. It ships with a BCG and charging handle, though this build swaps in dedicated parts for both.

Buy

AlternativeDaniel Defense M4A1 RIS II Upper Receiver Group 14.5"$1,544.00

The RIS II quad rail with a low-profile gas block gives a truer modern SOCOM Block 2 look and drops the fixed front sight post for a cleaner optic rail.

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Lower Receivers

Aero Precision M4E1 Stripped Lower Receiver

$155.00 MSRP

The Aero Precision M4E1 stripped lower is the most popular upgrade receiver for a reason. The threaded bolt catch pin installs with a hex key instead of a hammer and roll pin, the integrated trigger guard cannot snap off, and the upper tension screw removes receiver wobble against the DD upper for a tighter feel.

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Bolt Carrier Groups

Daniel Defense M16 Bolt Carrier Group

$235.00 at Optics Planet · In stock

The Daniel Defense M16 bolt carrier group is built to the same spec as the carriers in DD's complete rifles: an 8620 carrier, a shot-peened and HP/MPI-tested Carpenter 158 bolt, chrome-lined interior, and a staked gas key. The full-auto M16 profile carries the mass that keeps the gun cycling through the fast strings this build is designed for.

Buy

Budget swapBCM Bolt Carrier Group$223.99

BCM's phosphate full-auto BCG uses the same C158 bolt and staked gas key for less money if the DD branding is not a priority.

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Triggers & Fire Control

Partisan Triggers Disruptor FRT

$275.00 at Optics Planet · In stock

The Partisan Disruptor is the heart of the build. It is a forced reset trigger with a three-position safety and a listed 3.75 to 4.1 pound pull. In its enhanced-semi mode the bolt carrier's rearward travel physically drives the trigger forward into reset, so follow-up shots come far faster than a standard trigger while each pull still fires a single round. It needs an H2 buffer at minimum, with H3 recommended, on a carbine-gas gun like this one.

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Premium swapPartisan Triggers Disruptor FRT (Ambi)$299.99

The ambidextrous Disruptor adds a left-side selector for support-hand manipulation without changing the reset mechanism.

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AlternativeRare Breed Triggers FRT-15L3$450.00

The Rare Breed FRT-15 is the original forced reset trigger design if you want the name that started the category.

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Charging Handles & Action Controls

Radian Raptor-LT Charging Handle

$73.99 at Optics Planet · In stock

The Radian Raptor-LT is a 1.2-ounce ambidextrous charging handle with large, textured latches you can strike with a thumb, finger, or palm. Under a holographic sight that sits close over the receiver, the ambi levers make press-checks and malfunction clearances far easier than a standard right-side latch.

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Budget swapBCM Gunfighter Charging Handle$79.79

The BCM Gunfighter's extended Mod 4 latch improves manipulation for less if you do not need ambidextrous operation.

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Pistol Grips

Magpul MOE-K2 Grip

$18.90 at Optics Planet · In stock

The Magpul MOE-K2 uses a steeper 17-degree grip angle that brings the firing hand closer to the body, which suits a squared-up stance and reduces wrist strain when running an aggressive, C-clamp hold during fast strings.

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AlternativeBCM Gunfighter Grip Mod 3$19.95

The BCM Gunfighter Mod 3 uses a more traditional reduced angle with a storage compartment if the steep K2 angle does not fit your hand.

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Stocks & Braces

B5 Systems Enhanced SOPMOD Stock

$79.99 at Optics Planet · In stock

The B5 Enhanced SOPMOD gives the widest cheek weld in B5's lineup at 11.8 ounces, with dual water-resistant compartments that each hold three CR123 cells. The wide comb supports your face under the raised holographic sight, and the battery storage keeps spares for the EXPS3 and light on the gun.

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Budget swapMagpul CTR Carbine Stock$59.95

The Magpul CTR drops to 8.8 ounces with a friction lock that kills wobble, trading cheek support and storage for lighter weight.

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Optics & Sighting

EOTech EXPS3 + G33 Magnifier Combo

$1,279.00 at Optics Planet · In stock

The EOTech EXPS3 and G33 combo delivers a fast 1x-to-3x optic setup: the EXPS3's 68 MOA ring with a 1 MOA center dot for instant close-range aiming, and the G33 3x magnifier on a switch-to-side mount that flips into place behind it for identification and precision past 200 yards. Both units are night vision compatible and quick-detach. The system runs around 22 ounces with mounts, which is the weight cost of this versatility.

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Budget swapEOTech EXPS3$733.99

Run the EXPS3 holographic sight alone and add the G33 later; you keep the fast 1x window and drop the magnifier's weight and cost.

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AlternativeVortex Razor HD Gen II 1-6x24$1,469.00

A 1-6x LPVO gives continuous magnification and a BDC reticle, trading the holographic sight's true-1x speed for glass-based precision.

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Magazines & Feeding

Magpul D-60 Drum Magazine

$127.95 at Optics Planet · In stock

The Magpul D-60 holds 60 rounds in a compact drum with a ratcheting loading lever and the proven Gen M3 feed tower. For a sustained-fire role, it keeps the FRT fed through long strings without the interruption of frequent 30-round reloads, at the cost of 46 loaded ounces hanging off the magwell.

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Budget swapMagpul PMAG 30 AR/M4 GEN M3$13.95

A standard 30-round PMAG Gen M3 cuts weight and cost when you do not need the drum's capacity for a range session.

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Current build cost $3,795.83

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Capability profile

Capability Scan

Baseline vs Configured

Frequently Asked Questions

▶Is a forced reset trigger like the Partisan Disruptor legal?

The Partisan Disruptor is a semi-automatic forced reset trigger, meaning each trigger pull fires exactly one round; the bolt carrier just resets the trigger faster than your finger can. After Cargill v. Garland (2024) forced reset triggers are treated as semi-auto at the federal level, but several states restrict or ban them, so verify your state and local law before buying. It is not a machine gun and not a binary trigger.

▶Can I build this Block 2 IAR cheaper?

Yes. Swap the EOTech EXPS3 and G33 combo for the EXPS3 holographic sight alone and add the magnifier later, drop the Daniel Defense M16 BCG to a BCM phosphate carrier, run a Magpul CTR stock instead of the B5 Enhanced SOPMOD, and load standard 30-round PMAGs instead of the D-60 drum. The Partisan Disruptor and the DD quad-rail upper are the parts that define the build, so keep those and economize on the surrounding components.

▶What buffer do I need to run the FRT reliably?

Partisan lists an H2 buffer as the minimum for carbine-gas guns like this 14.5-inch DD upper, with an H3 buffer commonly recommended for the most consistent forced reset. The extra buffer mass slows the carrier enough to make the reset dependable. A rifle-buffer setup applies only to 20-inch A2-style systems, not this carbine.

▶Why a holographic sight and magnifier instead of an LPVO?

A red dot or holographic magnifier combo keeps a true 1x sight for both-eyes-open close-quarters speed and only adds 3x magnification when you flip the G33 in. An LPVO gives continuous magnification but its eyebox and true-1x fidelity are more demanding at speed. For a sustained-fire IAR role where most work is close and fast, the EOTech EXPS3 plus G33 is the faster answer.

▶Does the 14.5-inch barrel make this an SBR?

No. The Daniel Defense M4A1 FSP upper uses a 14.5-inch barrel with a Surefire SF3P muzzle device pinned and welded to reach a permanent 16-inch barrel length, which keeps it a standard rifle with no NFA paperwork. If you chose a bare 14.5-inch barrel without a pinned device, it would be a short-barreled rifle; under current law the federal making tax on an SBR is zero, but you still file the paperwork and wait for approval.

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