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A guide to upgrading AEGs, please use before asking questions.

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  • A guide to upgrading AEGs, please use before asking questions.

    This is fairly basic, I'm not going to go into fine tuning, or modding of various gearboxes. For this, I am assuming that the stock internals are of Marui or equivalent standard, purely because clone internals vary too much in quality to make a general guide on them.

    FPS (Feet Per Second, speed of bb)

    New Spring:

    This is the easiest and most common way of increasing FPS. Most lower power springs can simply be dropped in without worry, and will do no damage to your gun. You will notice a very slight decrease in ROF (Rate of Fire), due to the higher resistance of the new spring.
    However, higher power springs (>M100) will probably need you to replace other internals to prevent your gun from breaking due to the power of the spring. I will talk about this later.

    The rough power output of springs follow. Please bear in mind that this depends on the quality of your air seal, and thus these readings differ from gun to gun. It will also differ from brand to brand (of spring). Thus I am assuming all springs are Systema, in a stock Marui:

    1J: 328FPS~
    M100: 350FPS~
    M120: 390FPS~
    M120S: 420FPS~

    For more details, please use Google.

    Tight Bore Barrel:

    Simply, a barrel with a smaller inner diameter. The most common used is a 6.03, but there are a lot of diameters available. A 6.01 will need very, very regular cleaning, and is only recommended for single shot rifles. These can increase velocity by about 5-10FPS. Doesn't seem worth it? They increase range and accuracy far more. More about this later.

    Air Seal Upgrades:

    Fairly broad, this one. Your air seal is a combination of:

    Hopup (inc. rubber)
    Cylinder (and head, inc. rubbers)
    Piston Head
    O Ring

    I can't really give a value for how much this will increase FPS by, as it depends on how much you upgrade, and how bad your air seal was to begin with. If you air seal is in desperate need of upgrading, you will know, as the FPS of your gun will greatly reduced.

    Other Things To Think About:

    A bad hop unit, when set, will rob the gun of FPS. G&P hop units have been known to do this.
    An unclean barrel will destroy accuracy as well as drop your FPS.
    An unclean gearbox can lose you FPS and ROF.


    Something to note: the length of your barrel will provide no descernable performance improvement. A lot of people will say "oh a longer barrel gives more range/accuracy", thich may be true of real steel rifles, but is absolute bull in airsoft. The only time a barrel length change will have a difference is if you don't match the gearbox cylinder to the new barrel. You'll lose a lot of performance if you don't change the cylinder out as well.


    Surprisingly, FPS doesn't have as much an effect on range as most people think. Granted, an increase of 150FPS will give you more range, but most of it comes down to quality of hop unit, as is explained.


    The Hopup upgrades come into three parts, chamber (the casing), rubber (the sleeve that fits over the barrel), and the bucking (the small nub that applies hop). If you know them by different names, then that's fine, but to avoid confusion I shall refer to them as I just have done.

    The rubber. It comes down to preference. I very much like TM rubbers, they are fantastic. Guarder clear are also very nice. Shop around and read reviews.
    The bucking. "H" buckings are very good indeed, these also increase accuracy. A very good, cheap way of fixing (not upgrading) a broken bucking is to use a bit of the inside of a Biro (not the bit with the ink in it). Cut it to size, and drop it in.
    The casing. Not desperately important. I myself would only get a new one if my current one wasn't working. Again, TM is a good choice.

    A good Hopup unit will increase range and accuracy a lot, and as stated before, will not rob your gun of FPS.

    Tight Bore Barrel:

    Very nice upgrade, will improve range and accuracy. They are a fair bit of money, but are worth it considering that they improve three aspects of gun performance without putting much extra stress on the internals.



    Again, Hopup. A good Hopup will give tighter groupings as the BB will fly straighter.

    Tight Bore Barrel:

    This is where this upgrade really comes into its own. A tight bore can make your gun far more accurate. Again, a 6.03 is the most popular choice. Make sure you choose the correct length for your gun (use Google).

    ROF (Rate of Fire)


    Simplest way to upgrade ROF. A TM EG1000 (or equiv.) will satisfy most, and you won't need to replace any internals to accommodate the increase. Make sure to get the correct shaft length for you gun (again use Google). Systema motors, whist giving very nice ROFs, will require you to upgrade their internals. I will talk about this later.


    Low resistance wiring is a very healthy way to upgrade ROF. It will also put less strain on the electrical parts of the gun, and mean that they don’t get as hot.


    Very simple one this; the higher the voltage, the faster the ROF. Most guns come standard using an 8.4V, and you should be absolutely fine to drop in a 9.6V, which will satisfy most. However, going higher (10.8V, 12V) without upgraded internals will more than likely damage your gearbox.

    Also, higher mAh of battery will also increase ROF, though not by as much. This is due to the battery having less resistance with higher mAh (assuming constant voltage).

    High Speed Gears:

    These work in conjunction with high-speed motors. They are designed to allow faster rotation, and less resistance. Not as effective without a new motor, but very effective with one.


    Whichever you want to call them. These are the small bits of metal/plastic that the gears sit in. They come in three main sizes: 6mm (standard), 7mm and 8mm. The last of these are designed for very high speeds, and are very nice if you can get your hands on them. However, there isn't much choice here, as you gearbox casing will only take one size. My advice is to just get metal ones of whatever size your gearbox will accommodate.


    This isn't an really an upgrade. Shims are the very thin washers of metal that sit between the gears and bushing/bearings, on the gear axle. They are used to correctly position the gears. Too close together and the flat faces of the gears will rub together, causing resistance. Too far apart and only the corners of the gear teeth will be engaged with one another, resulting in them shredding. Also, too many shims on the same axle will cause friction, and add resistance. As you can probably gather, shimming is quite a precise thing. It is best just to leave the stock shims where they are unless you know what you are doing.

    A Weaker Spring:

    Simple, reduces resistance, and thus a higher ROF. However, problems can occur with this, as with ROF upgrades in general. I will talk about these later.

    A Clean Gearbox:

    A cleaner gearbox will reduce resistance as well as chances of jamming.

    There are other things you can do to increase ROF, drilling holes in the piston to make it lighter is an example, but they tend to be mods as oppose to standard upgrades, so I'll leave them alone.

    The Bits I Said I'd Talk About Later:

    High Power Internals:

    Simply put, a high power spring is going to exert a much larger force on the components used to pull it. Thus, if said components are bad quality, they are going to break, and you are going to have bits of metal flying around your gearbox. High-torque is the name for internals designed to take high amounts of stress. To run a high power spring, you will need:

    High Torque Gears
    High Torque Motor
    A High Stress Piston.

    At this point, it may seem tempting to get a metal piston. DON'T. The piston acts as a mechanical fuse. If something is wrong in your gearbox, or it jams, then the piston will go as oppose to your gear set/motor. Pistons are cheap, gear sets and motors are not. Thus you'd rather have a piston go than your gear set.

    High Speed Issues:

    The main issue with high speed is pre-engagement.
    The piston is drawn back and released.
    When the piston is released, the gears now have very little resistance, and under a high speed setup will turn extremely quickly. If the spring is weak enough, and the ROF high enough, the sector gear will re-engage the piston as the piston is still travelling forward. This will cause the piston to break very quickly. There is a mod that avoids this, and whilst quite simple in theory, is easy to get wrong, and is best left to an experienced techy.

    High speed motors work best with high speed gears, but that will then need fine tuning to run reliably. I find that unless you are looking to go for a very high ROF, don't stray beyond a Classic Army high speed/G&P M120 motor speed.

    Gearbox Versions:

    Unsurprisingly, AEGs don't all have the same shape gearbox. Whilst they all run with the same basic design (motor, three gears, piston, cylinder etc), they are shaped very differently from gun to gun.

    You should only put upgrades designed for that version gearbox into your gun. Some retailers have "for M16" or "for AUG", as oppose to the version of the gearbox, which is obviously more useful, but it is recommended that you find out your gearbox version before upgrading. Again, Google is your friend here.

    Hope the above helps newbie’s seeking to upgrade AEGs. Thanks for reading.
    Last edited by The Keeper of Secrets; 4th June, 2010, 13:16. Reason: spelling

  • #2
    Re: A guide to upgrading AEGs, newbies please use before asking questions.

    Picture labelling parts of a V2 gearbox. The only part I talk about not pictued is the piston head (and thus O ring), concealed by way of being inside the cylinder.


    • #3
      Re: A guide to upgrading AEGs, please use before asking questions.

      hey mate, excellent step by step way to a GB. i have a question regarding high speed issues. now im putting a MOSFET in my SPR which has aG&P m120 motor, guarder FTK and systema m100 spring. obviously with the mosfet and the speedy stuff its gonna be running around 28-31RPS with a 9.6 3300Mah battery.
      now you said the way on combating the problem is to mod something in the GB. by any chance is that removing the back 2 teeth on the piston? that way you dont get premature sector gear engagement?


      • #4
        Re: A guide to upgrading AEGs, please use before asking questions.

        There are a few things needed to be done to get a high speed gearbox to last.

        1. First important step is to correct the angle of engagement.
        This is when the first gear tooth hits the first tooth on the piston. What you want it to do is hit it flat ,so most of the impact is spread across the hole tooth, insted of it impacting it at an angel and on a small area. To do this you use spacers between the piston and piston head to lengthen it. Here are some pics i found as i dont have any i could take.

        This is the piston with spacers to correct angle of engagement, and also short stroked as you can see a plastic tooth has been removed and the metal one moved down in its place.

        Bad angle of engagement.

        Good angle of engagement.

        2. Secondly you can swish cheese the piston to lighten it and also remove the berings on the piston head if it had them, thios will also reduce weight. The reduction in weight helps the piston move to its stock position faster, so it wont be picked up prematurely.

        3. And a third step is to short stroke the piston and gear.
        This involves removing the last plastic tooth on the piston and moving the the metal one up in its place (see first pic), and then also removeing a tooth on the selecter gear. This will reduce your fps and slitly increase rof but it will also help stop the piston from beaing striped.


        • #5
          Re: A guide to upgrading AEGs, please use before asking questions.

          Also one thing i would say about barrels is the tighter you go the more range you get but less accuracy and the wider, the less range but better accuracy.


          • #6
            Re: A guide to upgrading AEGs, please use before asking questions.

            im not short stroking i know about that, but i was told bout angle of engagment that ill do at a late date. i see the last 2 teeth have been removed.
            thanks turtle dude:D


            • #7
              Re: A guide to upgrading AEGs, please use before asking questions.

              Remember those first 3 pics^ are thanks to Corvid

              You only have to shorten those 2 teeth if you have spaced the piston assembly back for corrected angle of engagement, they need to be modified so that they do not interfere with the sector pickup tooth.

              If you are not adjusting the pistons position (correcting AoE), i don't advise removing both teeth, shave down just the one. The additional clearance that removing the two teeth gives should not necessarily be used as a fix for premature engagement, all it will mean is that should a gear timing issue occur, the sectors initial pickup tooth will attempt to engage the piston tooth whilst the piston is still returning, potentially breaking it off.
              This is why you often see pistons with the back ends ripped off. All those harder polycarb pistons get the worst end of this as they are often too brittle to withstand the small margins of error, this is one of the reasons why the Systema piston has a bad rep, and one of the reasons why people often take the softer TM piston over it.

              Using a stiffer rated spring (Systema M100 should be fine) and or lighter bbs (i.e not exceeding .20gs) will be a better fix.

              Short stroking is not necessary at this speed + said spring rate, whats more he's using an SPR - longer barrel, he wont appreciate the reduction in usable cylinder volume, especially not on top of AoE corrections.


              • #8
                Re: A guide to upgrading AEGs, please use before asking questions.

                o dear
                Student Of Master Fong


                • #9
                  Re: A guide to upgrading AEGs, please use before asking questions.

                  May I use this guide on another forum? All credit to you guys.


                  • #10
                    Re: A guide to upgrading AEGs, please use before asking questions.

                    yer im gonna do all the AoE stuff, i tryed it on my dboys box and that still works, except it locks up now and then cos the pinion gear come off:D


                    • #11
                      Re: A guide to upgrading AEGs, please use before asking questions.

                      Does anyone know what size bushes are in the JG Ver3 gearbox?

                      I have a new spring but might as well do the bushes at the same time.


                      • #12
                        Re: A guide to upgrading AEGs, please use before asking questions.

                        Should be plastic 6mm if it's a stock one.


                        • #13
                          Re: A guide to upgrading AEGs, please use before asking questions.

                          can you put a 12v Battery in a ics mp5 a4


                          • #14
                            Re: A guide to upgrading AEGs, please use before asking questions.

                            If you want it to explode into a million parts.....

                            A 9.6v battery will give you plenty of extra speed. With a G&P M120 motor you'll be looking at 23 a sec with 8.4v and nearer 30 with the 9.6v.


                            • #15
                              Re: A guide to upgrading AEGs, please use before asking questions.

                              Am I a bad person not going into my guns, scared that I'll break it?
                              Lots of my comrades say that I should open them up to service them...


                              About the Author


                              The Keeper of Secrets TreadStone Captain and Team Sniper. Find out more about The Keeper of Secrets