Flex 3MR Rifle Trigger

What Is the Flex 3MR Trigger?

If you own an AR15 and you’re looking for a way to shoot faster, more accurately, and more confidently, the Flex 3MR Trigger is one of the most talked-about upgrades in the firearms community right now — and for very good reasons.

The Flex 3MR is an assisted reset trigger made by Flex Industries for the AR15 platform. It was designed from the ground up to give shooters — especially law enforcement officers and tactical operators — a faster, smoother, and more reliable trigger experience without crossing into illegal territory. In fact, the Flex 3MR holds the unique distinction of being the only ATF-approved assisted reset trigger on the market today.

The Story Behind the Flex 3MR Trigger

According to Flex Industries, the Flex 3MR was developed out of a critical operational need to provide a superior fire control unit for professionals engaged in border enforcement and counter-cartel operations. The men and women protecting the U.S. borders face fast-paced, high-stress, life-or-death situations where the difference between a fast follow-up shot and a slow one can be the difference between life and death.

Existing trigger systems simply weren’t cutting it in these conditions. Standard triggers were too slow to reset under stress. Fully automatic options were too hard to control in terms of accuracy and ammunition usage. What was needed was a trigger that could fire rapidly, reset reliably, and still allow the shooter to maintain precise target engagement.

The Flex 3MR was engineered to solve exactly that problem. It draws on the legacy of TAC-CON’s 3MR technology, which had received ATF approval as an assisted reset trigger that doesn’t classify as an automatic weapon, and builds upon it with new engineering refinements to produce the most advanced and compliant rapid-fire trigger system available to civilian and professional markets today.

The result is a trigger that is battle-tested, rigorously engineered, and now available to AR15 owners across the United States.

Key Features of the Flex 3MR Trigger

Here’s a breakdown of what makes the Flex 3MR Trigger stand out from the crowd:

ATF Approved — Fully Legal Under Federal Law

The Flex 3MR is the only ATF-approved assisted reset trigger on the market. Every purchase comes with an official ATF approval letter confirming that this trigger system is fully compliant with federal regulations and does not classify as an automatic weapon or machine gun.

3-Position Ambidextrous Safety Selector

The Flex 3MR includes a 3-position ambidextrous safety selector, making it accessible for both right-handed and left-handed shooters. The three positions give you:

• Safe – the firearm will not fire
• Semi – standard semi-automatic fire
• Third Position (Assisted Reset) – engages the assisted reset mechanism for rapid follow-up shots

Assisted Reset Mechanism

The heart of the system. When engaged in the third position, the trigger uses energy transferred from the bolt carrier group through the trigger assembly to actively push the trigger back to the front sear after every shot. This produces a crisp, fast, consistent reset.

4.5-Pound Non-Adjustable Trigger Pull

Both the semi and third positions have a consistent, non-adjustable 4.5-pound trigger pull weight. This is firm enough to prevent accidental discharge while still being light enough for controlled, rapid fire.

Drop-In Compatible with Mil-Spec Lower Receivers

The Flex 3MR is designed to work with mil-spec lower receivers, making it compatible with the vast majority of AR15 platforms available in the United States today.

Requires M16/FA Bolt Carrier Group

To engage the assisted reset function, the Flex 3MR requires a full-auto (FA or M16) bolt carrier group. This is necessary because the BCG is what provides the force to actuate the assisted reset. (Note: Using an M16 BCG in a semi-automatic lower is completely legal.)

Built for Extreme Durability

The Flex 3MR is purpose-built for use in the most demanding tactical environments. Its materials and construction are designed to resist corrosion, heat, and wear, ensuring reliable performance under thousands of rounds and harsh conditions.

Rapid Follow-Up Shots with Precision

The combination of the assisted reset and the 3-position selector means that shooters can achieve faster, more controlled follow-up shots while maintaining excellent accuracy — something that forced reset triggers and binary triggers often compromise.

How the Flex 3MR Trigger Works

Understanding the mechanics behind the Flex 3MR makes it easier to appreciate why it works so well. Here’s a simplified breakdown:

Step 1 – You Pull the Trigger When you pull the trigger in any of the active fire positions (semi or third), the hammer drops and the round fires.

Step 2 – The Bolt Carrier Group Cycles As the round leaves the barrel, the gas-operated system drives the bolt carrier group rearward. This ejects the spent case and cocks the hammer again.

Step 3 – Force Is Transferred Here’s where the magic happens in the third position. As the BCG moves forward again after cycling, its kinetic energy is transferred through the trigger assembly — this force is directed to the trigger itself, physically pushing it back forward to the front sear (reset position).

Step 4 – The Trigger Resets Instantly Because the trigger is being assisted back to reset by the mechanical energy of the BCG rather than relying solely on spring tension, the reset happens faster and more reliably than with a standard trigger or even most aftermarket triggers.

Step 5 – You’re Ready to Fire Again With the trigger already in reset position, you can immediately fire your next shot with a simple pull — no need to consciously release and re-engage the trigger.

This cycle can repeat rapidly, allowing for a high rate of controlled fire that is still fundamentally semi-automatic in nature — one shot per trigger pull — which is why it is legally distinct from a machine gun under ATF definitions.

Who Is the Flex 3MR Trigger Built For?

The Flex 3MR was designed with specific users in mind, though its benefits extend to a wide range of AR15 owners:

Law Enforcement and Border Patrol Officers

This is the original intended audience. Officers operating in high-stress environments with threats that require rapid, accurate fire will find the Flex 3MR to be a genuine operational upgrade. The assisted reset function helps counteract fear lock and ensures that officers can engage threats effectively even under extreme stress.

Military and Tactical Operators

Special operations personnel and tactical teams who depend on their AR15-platform rifles in close-quarters or high-tempo environments will appreciate the speed and consistency of the Flex 3MR.

Competitive Shooters

3-gun competitors, USPSA shooters, and tactical match participants are always looking for a legal edge in their speed and accuracy. The Flex 3MR’s faster reset can shave fractions of a second off split times, which can be the difference between first and second place in competitive shooting.

Home Defense and Self-Defense Owners

Anyone who keeps an AR15 for home defense knows that if you ever need it, the situation will be high-stress and fast-paced. The Flex 3MR’s intuitive assisted reset can help ensure you can fire accurate follow-up shots even when your heart is pounding.

Enthusiast and Range Shooters

If you just love shooting your AR15 and want to experience what a top-tier trigger upgrade feels like, the Flex 3MR is a genuinely impressive piece of engineering. It makes every range session more enjoyable and more educational.

Flex 3MR vs Other AR15 Trigger Upgrades

The AR15 aftermarket trigger space is crowded. Here’s how the Flex 3MR stacks up against the most popular alternatives:

Flex 3MR vs Standard Drop-In Trigger

Standard drop-in triggers are great for improving pull weight, feel, and reset quality — but they do not have an assisted reset function. They rely entirely on spring tension. The Flex 3MR is in a different category because it uses mechanical assistance to speed up the reset, making follow-up shots faster. For pure precision shooting, a high-end standard trigger is excellent. For rapid, accurate fire, the Flex 3MR wins.

Flex 3MR vs Binary Triggers (e.g., Franklin Armory, Fostech)

Binary triggers fire one round on pull and one on release, effectively doubling your fire rate with each trigger action. However, this means firing a round when you release — which can be dangerous if you’ve already identified your target is no longer a threat. Binary triggers also face significant legal challenges in many states. The Flex 3MR fires only on the pull, giving you full control and a much better legal standing.

Flex 3MR vs Forced Reset Triggers (FRTs)

Forced reset triggers (FRTs) were popular for a time but have been classified as machine guns by the ATF and are now prohibited for civilian ownership. The Flex 3MR is specifically designed to be different — it assists the reset rather than forcing an automatic cycle — and it has ATF approval to prove it. There is no legal FRT product on the market; the Flex 3MR is the legal, compliant alternative.

Flex 3MR vs Standard Stock Trigger

No contest. The stock mil-spec trigger on most AR15s has a heavy, gritty pull, a mushy reset, and leaves a lot of performance on the table. Upgrading to the Flex 3MR is night and day — you get a cleaner break, a much faster and more mechanical reset, and the option to engage assisted reset mode when needed.

How to Install the Flex 3MR Trigger

Installing the Flex 3MR is within the capability of most AR15 owners who are comfortable doing basic lower receiver work. Here’s a general overview of the process:

What You’ll Need:

• Flex 3MR trigger assembly (comes as a complete fire control group)
• M16/FA bolt carrier group (if not already installed)
• H2 or H3 buffer (if not already installed)
• AR15 armorer’s block or vise
• Roll pin punches
• Hammer
• Needle-nose pliers (optional but helpful)

General Installation Steps:

Step 1 – Clear and Safety-Check the Firearm Always verify the rifle is completely unloaded before beginning any work. Remove the magazine, lock the bolt back, and visually and physically inspect the chamber.

Step 2 – Separate Upper and Lower Receivers Push out the two takedown pins and separate the upper from the lower receiver.

Step 3 – Remove the Old Trigger Group Using the appropriate punch, push out the trigger pin and hammer pin. Remove the trigger, hammer, disconnector, and associated springs.

Step 4 – Install the Flex 3MR Following the instructions provided with the Flex 3MR, install the new trigger and hammer assembly, ensuring all pins seat fully and all springs are oriented correctly.

Step 5 – Install the 3-Position Safety Selector Remove the existing safety selector and replace it with the Flex 3MR ambidextrous 3-position selector. Make sure it detents cleanly into all three positions.

Step 6 – Reassemble and Function-Check Reassemble the lower, reattach the upper, and perform a complete function check. Cycle through all three safety positions, test the hammer fall in each fire position, and verify the safety locks the trigger in the safe position.

Step 7 – Install Compatible BCG and Buffer (If Needed) If you don’t already have an M16 BCG and H2/H3 buffer, now is the time to install them.

Step 8 – Test Fire Head to the range and run at least two magazines in semi mode before engaging the third position assisted reset. This lets you get a feel for the base trigger before experiencing the assisted reset function.

Flex 3MR Trigger Maintenance and Longevity

Like any precision mechanical component, the Flex 3MR benefits from regular maintenance. Here are some tips to keep it running at peak performance:

Keep It Clean Carbon buildup in the trigger pocket area can affect the smoothness of the reset. After every shooting session — or at least every few hundred rounds — clean your lower receiver’s fire control group area with a good solvent and a bronze brush.

Lubricate Properly Apply a small amount of quality firearm lubricant to the trigger and hammer pins, the disconnector contact surfaces, and the selector detent. Don’t over-lubricate — excess oil attracts dirt and debris.

Inspect for Wear Periodically inspect the sear surfaces on the trigger and hammer for wear. The Flex 3MR is built for durability, but like all mechanical parts, it will eventually show wear with heavy use. If you notice any rough or inconsistent trigger behavior, inspect the parts before your next shooting session.

Check Buffer and BCG Because the assisted reset function depends on proper BCG cycling, keep your bolt carrier group and buffer clean and properly lubricated as well. A dirty or sluggish BCG can affect how reliably the assisted reset engages.

With proper care, the Flex 3MR is built to last tens of thousands of rounds.

Where to Buy the Flex 3MR Trigger

The Flex 3MR Trigger is available through several channels:

Direct from Flex Industries (flexindustries.com) Buying direct from the manufacturer is always a great option. You get the genuine article, access to customer support, and any promotions they’re running. The official website also provides the most up-to-date product information, including any new variants like the AMBI version with the ambidextrous selector.

Authorized Retailers The Flex 3MR is available through various authorized gun dealers and online retailers across the U.S. Look for retailers who include the original ATF approval letter with purchase — this is a sign they are selling the authentic product.

Tactical and Firearms Specialty Shops Many tactical-focused firearms retailers carry the Flex 3MR in stock. Check with your local FFL dealer or gun shop to see if they carry it or can order it for you.

What to Avoid Be cautious of third-party marketplace listings on platforms like eBay or unverified websites offering the Flex 3MR at steep discounts. Counterfeit trigger components can be dangerous. Always buy from reputable sources and confirm that your purchase includes the authentic ATF approval letter.

Flex 3MR Trigger Legal States: Where Can You Buy It?

While the Flex 3MR is federally legal across the United States, certain states have their own firearms laws that prohibit or restrict the sale of products like the Flex 3MR to civilians. As of the time of writing, the Flex 3MR is not available for civilian sale in the following states:

• California (CA)
• Connecticut (CT)
• Washington D.C. (DC)
• Delaware (DE)
• Hawaii (HI)
• Iowa (IA)
• Illinois (IL)
• Massachusetts (MA)
• Maryland (MD)
• Minnesota (MN)
• New Jersey (NJ)
• New York (NY)
• Rhode Island (RI)
• Washington (WA)

If you live outside these states, you can legally purchase and use the Flex 3MR Trigger. However, it is always your responsibility to check your local and state laws before making any firearms accessory purchase. Laws change, and what is legal today in your state may be subject to revision. Consult your local FFL dealer or an attorney if you have any questions about compliance.

Flex 3MR Trigger Frequently Asked Questions (FAQ)

Q: Is the Flex 3MR Trigger legal? A: Yes. The Flex 3MR is federally legal in the United States and comes with an official ATF approval letter. However, it is not available for civilian sale in certain states including CA, CT, DC, DE, HI, IA, IL, MA, MD, MN, NJ, NY, RI, and WA. Always check your state and local laws.

Q: Does the Flex 3MR make my rifle fully automatic? A: No. The Flex 3MR is an assisted reset trigger, not an automatic trigger. It still fires one round per trigger pull. The assisted reset simply makes the trigger return to its reset position faster, using energy from the bolt carrier group. This is why it is ATF-approved.

Q: Do I need an M16 BCG to use the Flex 3MR? A: Yes. The assisted reset function in the third position requires a full-auto (M16/FA) bolt carrier group. A semi-auto BCG will not actuate the assisted reset properly. Note: Using an M16 BCG in a semi-auto lower is completely legal.

Q: What buffer do I need? A: The Flex 3MR works best with an H2 or H3 buffer. Using an H1 or carbine buffer may result in unreliable assisted reset performance.

Q: What is the trigger pull weight? A: The Flex 3MR has a non-adjustable 4.5-pound trigger pull weight in both the semi and third positions.

Q: Can left-handed shooters use the Flex 3MR? A: Yes. The Flex 3MR comes with an ambidextrous safety selector, making it equally easy to use for both right-handed and left-handed shooters.

Q: Does every purchase come with an ATF approval letter? A: Yes. Every Flex 3MR purchase includes an official ATF approval letter confirming the trigger’s legal status as an assisted reset trigger, not a machine gun.

Q: How is the Flex 3MR different from a forced reset trigger (FRT)? A: Force reset triggers were classify as machine guns by the ATF and are illegal. The Flex 3MR is an assist reset trigger — it assists the trigger back to reset but does not force an automatic fire cycle. Every shot still requires a deliberate trigger pull. This distinction is what makes the Flex 3MR legal.

Q: Is the Flex 3MR compatible with AR10 platforms? A: The Flex 3MR is specifically design and marketed for the AR15 platform. Check with Flex Industries directly for information about compatibility with other platforms.

Q: How difficult is it to install? A: For someone familiar with basic AR15 lower work, installation is straightforward. It’s a drop-in replacement for the standard fire control group, plus installation of the 3-position safety selector. If you’ve never worked on a lower receiver before, consider having a gunsmith install it.

Technical Specifications