TFB REVIEW: Franklin Armory BFSIII Binary Trigger For H&K Firearms

    Until about two months ago, I had no intention of ever pulling a binary trigger. Seemingly serving no useful purpose, I viewed these fire control designs as gimmicky and on par with bumpfiring at hip level using a thumb-in-a-belt-loop stance. But when an Instagram follower and reader suggested that TFB review the new Franklin Armory BFSIII binary trigger for HK style guns, I had a sudden and dramatic reversal of thought. What if I could achieve near fully automatic rates of fire in multiple platforms without investing tens of thousands of dollars in a registered trigger pack? The bosses approved and TFB was lucky enough to receive a pre-production version of Franklin Armory’s newest trigger.

    So how did it do? Let’s find out.

    If you are unfamiliar with the binary trigger design, I’ll start off with the basics. The Franklin Armory BFSIII has three positions: SAFE – SEMI – BINARY. While the first two need no explanation, the third stop on the selector is where the magic happens. Pulling the trigger causes the hammer to fall and releasing the trigger also allows the hammer to fall. The result is two rounds fired as compared to a single round in “standard” trigger groups. Pulling the trigger in the Binary setting and holding it to the rear, then switching the selector to the Semi or Safe position will not result in a second round firing.

    The BFSIII (bottom) as it ships from Franklin Armory, an HK91/PTR91 trigger group, and the TPM Outfitters P5SD

    First off, if you are green to HK trigger pack maintenance, a few months ago we put together a primer on parts interchangeability and disassembly of the two most common groups found on the roller lock (delayed) platforms. I prefaced the write up as being “for dummies” because for one, I am not a gunsmith and two, a full disassembly of an HK trigger pack should probably be left to the professionals.

    All this is to say, there is some assembly required when you purchase a BFSIII. Not to worry, if you can install a trigger into an AR15 lower, you are more than capable of installing Franklin Armory’s new offering.

    The BFSIII is installed in the PTR Industries K3P above.

    The BFSIII is installed in the PTR Industries K3P above.

    BFSIII Parts and Installation:

    The HK BFSIII is sold as a bare trigger pack without a housing, ejector, ejector spring or ejector cam pin. This may come as a disappointment to some owners, however if Franklin were to include these items with each trigger, the costs would be passed on to you the buyer. Housings can run from $100-$300, ejectors are about $20, ejector springs are about $3 and ejector cam pins are about $3. The casual shooter can use the housing, ejector, spring and pin from their host weapon without buying any additional parts.

    For the more dedicated users, I recommend buying a separate housing, ejector, spring and cam pin from RTG Parts, Brownells or HKParts. This will allow you to swap between your standard trigger group and the BFSIII without the need for tools in less than a minute.

    Below is the BFSIII trigger pack with the ejector spring installed. I placed a spare ejector spring above it for reference. Honestly, binary trigger or not, if you own a HK style roller delayed gun, you should probably have a few of these on hand. They are small and held in place only with friction.

    The bottom front of the pack holds a long hex screw that is used to level out the assembly in some housings. My trigger ran fine with or without the leveling screw.

    PIctured are two ejectors, the top being for 9mm guns like the MP5 and the bottom being for .308 guns like the HK/PTR91 series. Below the ejectors is the ejector cam pin and the ejector spring. Again, if you own an HK style gun, invest the short money into a few replacement cam pins. They are small and only push-fit in place.

    Here we have the BFSIII selector (left), a S/F selector (middle) and an ambidextrous 0,1 selector (right). The Franklin Binary selector is held in place with two small hex screws. Disassembly starts by rotating the BFSIII selector counterclockwise to the 12 o’clock position. Then, using a 1.5mm hex wrench, loosen the right side screw and remove the right side selector. Once this is complete, you will be able to wiggle the left selector out of the housing/group and remove it completely. You may have to apply slight downward pressure on the hammer to free the selector completely.

    Pictured below is a standard S/F trigger pack (left) and the BFSIII binary trigger pack (right). Both packs have ejector springs installed but neither has an ejector or cam pin.

    Viewing the internal workings of the BFSIII trigger pack (left) and the S/F trigger pack (right), it’s easy to tell that there are some major differences. The Franklin Armory fire control unit resembles an AR15 Trigger group more than it does an HK trigger group.

    Each BFSIII will ship with two hammer springs. Below is the .308 hammer spring (left) and the 9mm hammer spring (middle). Note the extra coil on the .308 spring for added power. Using the 9mm spring in my PTR Industries K3P I experienced light primer strikes. Swapping out for the proper hammer spring corrected the issue completely.

    On the right is the BFSIII hammer and below are two collets that sit on the hammer pin inside the hammer spring coils. Again, disassembly and reassembly is much like an AR15 hammer – push the hammer pin out right to left, remove the hammer and spring, taking care not to lose the collets. Then swap out the hammer springs and use the included slave pin to keep everything together for re-installation. Tap in the hammer spring from left to right, pushing out the slave pin in the process.

    The whole process is easier than it sounds, taking two to three minutes to swap hammer springs. Besides, if I had to guess, the overwhelming majority of owners will run the BFSIII only in 9mm platforms, removing the need to change springs.

    If you haven’t already done so, take the time to read the “HK Trigger Pack Disassembly For Dummies” post I linked above. A lot of the steps I reference here are outlined in that basic tutorial.

    The Franklin Armory BFSIII For The H&K Platform:

    The BFSIII™ for HK is a 3-Position Trigger. In position 3 it will fire 1 round on Pull and 1 round on Release. This makes it the fastest semi-automatic trigger on the market. The BFSIII™ is ideal for Tactical and Competition use. The BFSIII™ provides greatly reduced split times between rounds and the ability to place two separate shots into a tighter group.

    Trigger Operation:

    Position 1 – Safe –Will not fire.

    Position 2 – Semi – Fires 1 round per pull.

    Position 3 – Binary – Fires 1 round on pull and 1 round on release.

    • A trigger pull around 4.5 pounds.
    • Ambidextrous Safety Selector.
    • Safety Selector will fit in two and three position trigger housings.
    • Will not work with Ambi Housings
    • Trigger housing, ejector, ejector pin and ejector spring are not included.
    • Will fit most HK 91, 93, & MP5 variants and clones
    • Some firearms may require additional fitting
    • MSRP $699.99

    A complete listing of all Franklin Armory installation and owners manuals can be found here.

    Shooting with the BFSIII Binary Trigger:

    With the installation out of the way, the “hardest” part is behind you. What’s left is some range time, practice and a lot of ammo.

    After years of practice on standard triggers, shooters may not be used to thebinary action of pulling to a full stop, holding and releasing as a secondary trigger pull. At first, the cycle of the BFSIII can seem counter intuitive; training your finger and your brain to make a complete two part cycle to fire two smooth shots. But with practice, I was able to simulate controlled strings of burst fire that turned live ammo into spent casings at speeds that makes my wallet cry. I used two platforms to test the BFSIII:

    1. The TPM Outfitters P5SD (MP5SD):

    I have to admit, I had reservations about adulterating my precious TPM rifle with “non-standard” parts. But the addition of Franklin’s latest binary offering made my favorite gun even more entertaining. It takes some getting used to and it has a different feel, but with practice I can empty a 30 round magazine in five to seven seconds.

    I experienced one stoppage that I can attribute to a magazine issue.


    2. The PTR Industries K3P from Atlantic Firearms

    My PTR K3P is still waiting for the ATF’s blessing to wear a stock. And while I should have ordered a pistol stabilizing brace instead of a surplus bipod, I decided to simulate HK G3 firing rates sans stock. Although the BFSIII functioned in the .308 platform without issue, my host gun was not in an optimal state for simulated automatic fire. Simply put, a short barreled battle rifle without a good shoulder/cheek weld is not a pleasant experience.

    Still, I was able to empty a standard 20 round G3 magazine in about five seconds, As you will see in the video below, the only stoppage I experienced was due to a few subsonic .308 rounds that snuck in at the end of the magazine.

    Most importantly, I didn’t experience an hammer follow (outrunning the action) in either gun, no matter how fast I attempted to pull and release the trigger.


    You’ll notice I avoided discussing utility or practicality in the review of the BFSIII. There will be those that will call binary triggers stupid or ridiculous. Without putting them behind a trigger, it is unlikely that I will be able to change their minds. But more to the point, most of us buy certain guns that have no real useful purpose other than pure entertainment value. Why can’t a trigger be in the same enjoyment-only category?

    Let’s talk about price. The $699 MSRP is a steep investment for entertainment. However, street prices are hovering between $500-$600. And with the money most HK roller gun owners have invested in their setups, $600 is not a terrible figure. For example, 0,1 ambidextrous trigger groups average about $300.

    All in all, the Franklin Armory binary trigger left me impressed. If you are an HK style rifle or pistol owner and want that feeling of near automatic rates of fire, the BFSIII is a worthy choice.

    What I think could be improved:

    1. A tool-less design for removing the selectors. I worry about loosing those small hex screws
    2. Include an ejector, ejector spring and ejector cam pin with each BFSIII. It will save the majority of users from having to disassemble their current packs to get up and running.

    What I liked:

    1. Works as designed. Functions on two major platforms.
    2. Well made.
    3. Fun. Smile inducing fun.





    Editor In Chief- TFB
    LE – Silencers – Science
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