Ben's mechanical hair trigger guide.

Discussion in 'Gun Building, Modifications & Repairs' started by Ben3721, Oct 4, 2019.

  1. Ben3721

    Ben3721 Well-Known Member

    This guide of mine used to be on another forum that is long gone. I am new to this forum, however many may know me from some old forums. Been teching for nearly 10 years. I hope this is an appropriate section for this guide. It will have to be broken down into multiple posts to get it all here. Please forgive me for triple posting, I had to to get the entire guide in. I used to keep this guide stashed away, but realized it needed to be public knowledge once again. It might not be bad to sticky this guide, while old school, it's the poor man's hair trigger without needing a 150 dollar trigger board.

    This is my personal hair trigger guide. It is more in depth than a typical guide, so I made the guide its own thread. I decided to make this because the old stickied hair guide has dead photos and isn't as in depth as this one. This guide is ONLY intended for a TM based V2 gearbox shell with a V2 based trigger assembly. I however assume the same principles can be adapted to work on other versions with a little bit of thought. This is a guide to HELP you make a hair trigger, you must already know how to use some basic tools and know how to open up a gearbox without killing yourself with the spring guide. I will not be accepting gearboxes to work on, do it yourself, that's what teching is about. If you cant work on your own gear your in the wrong hobby. I won't be holding anyone's hand to walk them through this guide other then the guide itself.

    Also please don't go full grammar nazi on this thread post. Don't quote the entire 3500 word thread post 9 times to point out every single typo, misspelled word or any detail I missed, please just PM me on here and ill fix it. I'm sure I messed up something on this massive thread. If you need any simple help or want to add something to this guide just PM me, don't reply it here. General questions and comments are welcomed.

    Now to the fun stuff and the start of the guide.

    I unfortunately also have to explain how semi works in detail since many newer techs may not know (I didn't know for a long time). By providing this info it should help some understand semi auto in a AEG, If you clearly understand how it functions you should be able to get the gist of how the hair trigger modification works. But first I will state some terminology by me that will be used here to help you understand what the heck I'm talking about.

    The terminology I have added below is to help describe certain sections of parts of which may be modified or that are very important to this mod. Don't worry I have attached photos at the end of the thread.

    Oddball Terminology List -
    cutoff lever sear: The section of the cut of lever that pushes the trolley sear up to slip it off the trigger sear, which resets the trolley back.
    Trolley: The piece inside the trigger assembly that holds the conductor contact bar, it interacts with the trigger sear and cut of lever sear.
    Trolley cutoff sear: The plastic section of the trolley that interacts with the cutoff lever sear, in this guide it will be replaced by a pin. So expect the term "trolley cutoff pin" to replace this term later on.
    Trigger sear: The top of the trigger that interacts with the trolley to push it forward until the trolley is kicked up by the cutoff lever to reset.
    Trolley reset pin/post: The pin/post (typically casted and part of the left side of the gearbox which often breaks off in stock guns) that stops the trolley when it resets back from being kicked off the trigger sear by the cutoff lever sear. The hair trigger mod will greatly reduce stress on this pin/post if done properly.
    Sector cam: The cam that pushes back of the cutoff lever.

    How semi auto works on a AEG (almost all types). I will also explain how auto bypasses this system.
    The trigger is pulled forcing the trigger sear to start pushing the trolley forward, the trolley cutoff sear then goes ABOVE the cutoff lever sear, (this MUST happen before the trigger contacts touch or it will fire auto for a moment!). Shorty after the trolley is pushed into the trigger contacts. Once the sector gear has released (or is about to release) the piston the sector cam hits the cut off lever, which then the sear of the cutoff lever pushes up the trolley cutoff sear high enough that the back of the trolley slips off the trigger sear and slams back into the trolley reset pin. This cuts power and the cycle is complete.
    For auto, the selector plate is pulled back from the selector switch, decompressing the selector plate spring and pulls the cutoff lever above the trolley reset sear. Preventing it from pushing the trolley sear up when it moves forward from the trigger pull.

    Tools/parts you will need.
    - Airsoft AEG with V2 gearbox and V2 trigger assembly. You must have decent trigger response already.
    - All the tools to take down the airsoft gun and gearbox your working on.
    - Easy cheap to replace trigger contacts (SHS) Not any with super sort trigger contacts. Just in case you screw up.
    - Dremel with 1 inch grinding cutting disk (you'll need a few) head and thick grinding disk head.
    - Eye protection, If you do not have any you shouldn't be playing airsoft lol.
    - Battery, not a high discharge rating one unless your careful to not short anything out. (for safety reasons). For those with mosfets don't use too low of a voltage or you can harm your mosfet.
    - Volt meter or motor or 12v led.
    - Small flashlight. No not your super bright 1500 lumen CREE one, you'll end up blind.
    - 6/32 tap, No.36 drill bit or a tad smaller, a few 6/32 screws with FLAT HEADS. This screw has a lot of surface area to its threads for its size and typically works the best. You have to decide what metal for the screw you want to use, because later you will have to grind down the head of the screw to about 1.5mm and still have some material left to be able to pull the screw back out if needed after heating the thread lock.
    - Mid strength thread lock, No high temp resistant stuff !
    - Good grease removing soap (dish soap) and your siblings tooth brush.
    - Gear grease.
    - Dark sharpie marker.
    - Drill or drill press. Must be able to drill a perfectish 90 degree hole.
    Optional but preferred.
    - Hand file and sand paper.
    - Retro Arms trigger. (will cut down time to do the mod a bit and you must have a nice trigger if you're going to be doing a awesome hair trigger...)

    Alright now I will begin the steps to do the mod. Please read the entire step before physically doing the step.

    Step 1: First you MUST remove most the slack between the trigger sear and trolley. Put the trigger in with the whole trigger assembly (with the trolley spring in) WITHOUT the trigger spring. Gently move the trigger back and forth. There will most likely be some wasted slack in the trigger pull that needs to be reduced. If by some dumb luck your trigger sear has about .5mm slack before hitting the trolley continue to step 2. If you are using a older Retro Arms trigger (or a rare handful of other triggers combined with certain trolleys) you may find that it's so far forward and tall that the trolley can't go back far enough to catch onto the sear to reset. It that is your case hand file the FRONT of the trigger sear (see image #1 I used a retro arms one) until you have about .5mm slack between them. You must have some slack to ensure the trolley is fully reset! Now for those with the stock triggers with tons of slack, You have many options to reduce this slack. Keep in mind LATER on you will want to sand the top of the trigger sear down shorter since it won't be pushing the trolley as far and doesn't need that extra height to push that far. I will list two ways below for those who have trigger slack between the trigger sear and trolley, a easy way and a harder way, read both.
    For those using Speed brand triggers (skip this paragraph if your not) you have a grub screw that you can one of two things with: to reduce this slack OR to set the maximum travel distance IN reinforced gearboxes with the extra lip (using a long screw and sanding it to set both will also work), for regular gearboxes without the lip you will need to still do step 3 and you will use the grub screw to reduce the slack. (see image #2)
    - (easy) Sand the back of the trolley (surface that is closer to the sector gear) until the slack is ALMOST gone, the trigger sear will then almost touch the bottom edge of the trolley where the notch is, however don't remove too much or the sear of the trigger sear will slip behind the trolley (like the retro arms triggers do out of the box). Be sure to use a weaker or pre-stretched trolley spring to prevent breaking your trolley reset post/pin in the long run. It must still be strong enough to reset the trolley back with the trigger sear under it.
    - (Best way, harder) First off some gearbox shells have a legit steel pin, if you have slack and have one of these reinforced pins already, use the "easy" method directly above. For others you must replace the stock trolley reset post with a screw after drilling and tapping the hole. Try to use a screw that is about the same size as the stock trolley reset post, and try to place it in the same spot. Once you have the screw in sand/dremel the edge of the screw until the trigger sear touches the trolley notch. Do not try to place the screw too far left or high or it will touch the cutoff lever and cause issues, if you did by accident take the cutoff lever and dremel out some material so that the cut off lever sits horizontal to the gearbox shell . Leaving the threads on the screw where the trolley hits WILL eat away the plastic within 10k rounds! (learned that the hard way.)
    I ended up doing a combination of both methods for my AEG's.

    Step 2: Cut out a slot on the top/back of the trolley to allow more space for the spring, this will smooth things out and prevent the trolley from hopping over the trolley reset pin/post. Later on shortening the trigger sear will also help prevent this. Don't shorten the trigger sear just yet...
    Last edited: Oct 4, 2019
    -Spitfire- likes this.
  2. Ben3721

    Ben3721 Well-Known Member

    Step 3: Trigger maximum travel distance.
    The trigger MUST have a screw to stop it early for it to be a hair trigger (duh) "Reinforced gearboxes" have a perfect spot with a lip that is meant to stop the trigger at a longer pull (see image #2 note that photo shows the screw and trigger already in). If you don't have that lip you will still be placing the screw in the same place. First dremel the head of a 6/32 screw so it's about 1.5mm thick then dremel a deeper slot for a flat head screw driver to fit into. If the head of the screw is too thick it will hit inside the lower receiver pushing your entire gearbox over (be sure to check this after you place the screw in). Drill a hole with a No.36 drill bit against the lip or in the same spot then tap the hole with a 6/32 tap, You want it to be a super short trigger pull for now, the back arm of the trigger should now almost touch the screw or even be in the way a bit. Tighten the screw as if your leaving it in (not so tight that you can't get it out...), no thread lock yet. If your screw is too long you will have to cut it down or it will go too far into the gearbox. You will soon be removing material off of the screw to set the maximum pull distance. Use the sharpie and mark where the back arm of the trigger hits the screw (see image #2), take out the screw, file/dremel off material until you achieve your desired trigger pull (see image #3). While setting your trigger pull consider this, the shorter the trigger pull, the harder it will be to set in the next few steps. I recommend not setting a trigger pull too short that you accidentally hit the trigger too fast and end up not completing full cycles, thus causing semi dead zone lockups more often. You must now use the soap+water and toothbrush to clean the gearbox shell from any metal fragments/dust/shreds. Dry it well and regrease any friction spots. It should now look something like Image #3 Remember to use thread lock when you finally put the gearbox together and know it's working fine, you can always take it out even when the gearbox is shut to do this. if you NEED it out heat up the screw to weaken the thread lock and use a nice screw driver or impact drill to remove it, DONT strip the head!

    Step 4: Placing the trolley sear pin.
    This is the hardest part about this mod, You may ruin a trolley forcing you to do step 1 and 2 again if you half-*** this step. This step requires a keen eye and a lot of focus.
    (See image #4) You soon must place a pin that is closer to the cutoff lever sear then the normal plastic sear. You essentially want it set to when the trigger is pulled that the pin IMEADTIATLY goes over the cutoff lever sear before the trigger contacts touch (see image #5) (next step will help with setting trigger contacts). Now to give yourself some room for error you'll want to use a pin a bit bigger then you'll need. You'll end up removing a tiny section of the plastic trolley sear and drilling a hole through the trolley at that spot and out the other side, Yes you may hit the metal bar inside the trolley that is the conductor for the contacts, use a sharp drill bit and oil it. (drill press really helps here). You want the hole a TINY bit smaller than your pin your using. (use a narrow nail as the pin OR a drill and tapped TINY threaded screw then cut the head off). If you using a pin rough it up and push it through with some thread lock, same if you use the screw thread lock it too. Once it's in place you must then make the end of the metal pin flush with the old plastic trolley sear remaining on the trolley (via dremel see image #4). And on the other side it must be flush to the plastic (via dremel again). Now take your dremel with a grinding cutting disk and make the disk smaller via grinding rock/metal and THEN shape the BOTTOM of the pin to be flush with the old plastic sear. Why would someone make the cutting disk smaller? Because if it's too big it hits the back of the trolley ruining it... learned that the hard way. Now that this is done put only this list of parts in: cutoff lever, selector plate and selector spring, trolley and trolley spring, trigger contact assembly, trigger and trigger spring. Close the gearbox, look down inside the gearbox like Image #5 You will see the two sears touching each other, hopefully they are too close and prevent you from switching the cut off lever up into auto via pulling back the selector plate (with trigger NOT pulled). Now you must go back in and remove material from either the cutoff lever sear or the trolley pin sear until the cutoff lever sear clears the pin when you switch to auto. try to make the edge of the pin and cutoff lever sharp so you don't get semi lock ups often (see image #4). You want the sears to BARELY clear each other! Now install the sector gear and close it back up. Make sure the selector plate is forward so that the cut off lever is down and ready. Pull the trigger a TINY bit, You should see the trolley pin sear (image #5) overlapping the cutoff lever sear almost immediately. Now rotate the sector gear a cycle, it will most likely bump the trolley up a little BUT not enough to kick it off the trolley sear, try this with the trigger all the way pulled. Don't freak out if it doesn't cut off yet. Step 6 is essential to this. Also don't try to lower the pin to try to make it cut off sooner, I won't explain what happens if you do atm, just don't it won't end up well.

    Step 5: Step removed.

    Step 6: Shortening the trigger sear JUST ENOUGH.
    Understand this, the trigger sear is no longer pushing the trolley as far, so more of the trigger sear is in contact with the trolley as the cutoff lever is trying to push the trolley up. Now if you skipped this step, your trolley could kick over your trolley reset pin/post requiring a full take down of the gearbox to fix, and it would pinch your trolley spring against your tappet if you didn't do step 2. So essentially in this step you want the trigger sear edge to just hang onto the trolley by like .3mm or so when the trigger is pulled to its maximum travel distance, sand/file the top of the trigger sear until this condition is met (don't make the edge too sharp it will wear the plastic off the bottom of the trolley over time). Keep in mind sanding too much off will cause the trigger to slip when pulled all the way EVEN without the cutoff lever touching the trolley pin sear, requiring another exact trigger and a re-try. Doing this all correctly makes it so when the cut off lever sear hits your new trolley pin sear, it kicks the trolley off the trigger sear with and back into its reset with MINIMAL uplift (this helps prevent some overspin as it cuts off faster). This is another reason why some remove material was removed from the back of the trolley for the spring slot; to prevent the spring from leveraging the trolley down making it less smooth. The trolley is being kicked up sooner than before and that's why this step was important in many ways.
    You should now be able to now push the selector into semi mode, pull the trigger almost any amount, roll the sector over a cycle and the cutoff lever should kick that trolley right over and reset it.

    Step 7: Setting the trigger contacts.
    Now that your almost done, I can tell you that you have finished all the stressful parts. Now you must bend the end of the trigger contacts (see image #6) so that when the trolley pin sear overlaps the cutoff lever sear (see image #5 again if you need too) ENOUGH that it catches reliably and doesn't slip. Now here's something that will help. Solder your wires to the trigger contact assembly properly , technically you never needed to remove the wires from the trigger assembly. Hook a volt meter or a cheap motor or ANY way you can know you have power to the motor power wires. Now hook up a battery as if your powering the gearbox, You must now bend those trigger contacts until they power on at the end of the trigger pull after the trolley/cutoff sears overlap. Make sure the ends of the trigger contacts are not perfectly strait as they could snag the edges of the trolley after they slide onto the conductor bar in the trolley. If they are too short then a longer conductor will have to be placed into the trolley or longer contacts. I should also add some use a micro switch for this function but they can be crushed and break.




    Note the material removed around the pin.

    You can see the cut off lever sear and trolley pin sear better in person. You will be able to see it at this angle.


    Congrats. You should now have a fully functional hair trigger on your AEG.
    I highly recommend a mosfet as you now have less trigger surface contact area.
    Troubleshooting section will be added later on. I may also add more photos later on.

    I have been using this gearbox for months mostly in semi, probably 80k rounds with only minor wear on the back of the trolley. Other then that the mod is solid.

    If you'd like to see a gearbox I did this mod in click this link for specs and a photo of the finished mechbox.

    Again you can do this mod to any mechbox with a direct trigger, v3 shells have a two piece trigger, which makes it nearly impossible to do this mod unless your detailed.
    Last edited: Oct 10, 2019
    kazuchan and -Spitfire- like this.

  3. Ben3721

    Ben3721 Well-Known Member

    Reserved third post for added content later on.