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M4A1 disassemby and gearbox breakdown (A peek inside)

  • 16-07-2011 12:09am
    #1
    Registered Users Posts: 4,612 ✭✭✭


    Had a dboys M4A1 lying in the wardrobe since 2007 that was
    wildly firing at all sorts of different fps levels,
    so decided I needed to open it up to see what was going on and perform a spring change.


    A lot of people are too nervous to open up their guns when they have an issue with them.
    The easy part is taking them apart and putting them back together again. The hard part is knowing
    how all the different parts interact with each other to achieve the result you want with regards to
    upgrades and repairs and tweaking. I'm confident enough to poke about and replace and try and fix things
    but I'm still clueless when it comes to brands and parts working together well,
    I don't have the experience or knowledge that an airsoft gun-tech would have so whatever I've mentioned
    below is from a NOOB's perspective.

    Decided to take a few photo's to show how easy it was to do a
    (very) basic M4 strip down to gear box level.

    I'll post the text first and the photo below the text in each pic.

    Its not a complete strip down of the gun or gear box and its not a trouble shooting guide but
    more of a very very very basic show and tell to encourage others to try fix their own issues
    if something goes wrong or at least to take a peak! :-)

    The M4 is common as Muck and nearly every airsofter will have one.
    The Dboys M4A1 uses a Version 2 gear box which is a nice bog standard easy one to work with.
    IMG_1619.jpg

    The Hand grip comes off easy as everyone will know who owns one.
    The butt comes off my pulling down on the lever instead of pushing on it.
    One thing to note here is a nice simple upgrade is to replace the crappy Tamiya (pictured)
    connectors with Deans Connectors. Tamiya connectors will only allow about 15amps of current through them
    so may actually act as a resistor for set ups that use better batteries that deliver a higher current.
    IMG_1620.jpg
    IMG_1624.jpg


    To separate the upper receiver from the lower receiver you only need to take out 1 Pin.
    This screws out with an Allen key. The nut screws out from the pin, and the pin can be removed.
    One side of the pin has a flat side that that rests against the receiver when installed which stops
    it from turning. Before trying to remove the upper receiver make sure you disconnect the wires
    from the battery connector switch (if your gun is front wired)
    These will sometimes have spade connectors to allow you to do this.
    IMG_1621.jpg
    [EDIT: The Cosmetic Bolt stop can be removed at this stage also if desired. After taking this gun apart
    and putting it back together a few times mine broke off as the metal is real cheap pot-metal]
    IMG_1622.jpg

    You can then slide the upper receiver forward taking care to slowly pull the wires through the
    opening in the reviver near the delta ring/end of the outer barrel.
    IMG_1623.jpg


    Once the upper and lower parts of the gun are separated you can just slide the inner barrel
    and hopup unit out of the outer barrel.
    IMG_1626.jpg
    IMG_1625.jpg
    IMG_1627.jpg



    I've a close up of the hop-up chamber here. When this is fully assembled its a good idea to
    wrap some Teflon tape AKA PTFE or plumbers tape. (not too much) while will help with air seals.
    IMG_1629.jpg
    IMG_1628.jpg



    Since I wanted...well needed more than wanted to open the gear box I was not concerned with
    stripping the upper receiver down any further so put it to one side. I just needed to take
    the gun apart enough to get the gearbox out.
    IMG_1630.jpg


Comments

  • Registered Users Posts: 4,612 ✭✭✭bullets


    Next step was to remove the Stock Tube. If yours has a cover, this can be removed.
    You can see in the pic of inside this tube below that there is a screw that needs to be removed
    internally. You will need a LONG screwdriver for this.
    IMG_1631.jpg
    IMG_1632.jpg


    Below is it removed. In the pic below you will see the Stock Ring.I've seen extended stock rings
    that have sling attachments on them, this ones standard. There is space on this to allow wires
    to pass through if you want to rear-wire your AEG instead of front wiring or vise versa.
    The metal part over the stock tube screw also is not 100% circular its got a tangent cut out of it
    so wires can pass down the inside of the tube.
    IMG_1633.jpg



    Next is take off the rear pin. Some AEG's have different sizes pins to the front pin.
    I don't know why.
    IMG_1634.jpg

    Next you want to remove the pistol grip and motor.
    You start be removing the screws on the Motor Plate.
    (you don't need to touch the large middle one)
    IMG_1635.jpg

    After you remove this you will see the motor.
    Some guns have a small metal disc for motor adjustment that sometimes
    falls out or gets stuck to the motor magnetically. My gun does not have such a disc.
    But its something to make note of if yours does. You can remove the wires on most
    motor's as they have spade/like connectors, some versions of gearboxes have horrifically soldered
    wires to the motors which is annoying as you need to desolder to get the motor out.
    IMG_1636.jpg

    This is the motor.
    There are different types Long, Short, High Speed, Hi Torque.
    On top of the motor the gear is called the Pinion gear.
    This motor is some cheap rubbish but it does the job.
    A replacement motor may cost in the region of 35-40 Euros and could be a good investment.
    From what I hear from more experienced airsofters than myself a lot prefer High Torque rather
    than high speed. Make sure you get the correct length of motor for your gun if you buy one.
    IMG_1637.jpg
    motors.jpg


    Be careful too when putting the motor back in that you connect it correctly.
    Some motor's connectors have a Red Colour painted on them for the red wire.
    IMG_1638.jpg

    Once the motor is removed, you will need a longish screw driver to loosen or remove two more
    screws in order to get the pistol grip off. On some pistol grips the screws will come out completely,
    other types the screws may stay partially threaded in the holes and allowing the pistol grip to be
    removed without having to take out the screws completely.
    (If the screws come out or fall out and you have a hard time trying to put them back in at the assembly stage
    a tip is to put a little silicone grease on your screw/screwdriver so it stick on)
    IMG_1639.jpg


    Nearly there! (Phew and nothing broken yet)
    There is still some things holding the gearbox in place.

    You will need to remove the magazine release catch.
    On the button side there will be a screw or an Allen screw.
    Remove this and the catch can be removed.

    Also on this side of the gun you will see a dummy cover/plate where the fire selector switch
    area. If you want (you don't need to) remove the fire selector switch you will need to remove
    this little bit in other to access a screw that's behind the fire selector switch on the inside
    of the receiver.
    IMG_1641.jpg


    Below is the mag release catch. This pin on this goes through a loop in the gearbox
    so this is why it needs to be removed.
    IMG_1642.jpg



    Lastly on some guns (not all) There is a pin that needs to be tapped out.
    This is not attached to the trigger in any way (although it looks like it is from the pic)
    IMG_1643.jpg

    A handy tool to have is a Jewelers or watchsmiths Hammer available from Maplin for under a tenner,
    its light and small and good for delicate taps, and comes with different heads such as a plastic head instead of
    a metal one etc.
    IMG_1644.jpg
    IMG_1645.jpg


  • Registered Users Posts: 4,612 ✭✭✭bullets


    Now you can take out the gear box.
    Its a good idea to turn your fire selector switch to Semi position to reduce the chance
    of damage to a plastic fire selector plate on the outside of the gearbox.
    Remove the gear box buy gently wiggling it diagonally away from the lower receiver.
    IMG_1646.jpg

    The fire selector plate is usually made out of plastic.
    There are different types for different types of guns.
    Some of these are easily damaged when taking the gearbox out while leaving the fire
    selector switch As the inside cam of the switch can catch on the plate.
    Not something you really need to worry about too much on an M4 but
    on an MP5 or SA58 worry!

    Now the belly of the beast! The gearbox.
    You generally have screw heads on one side so this is the side ya open.
    Its a good idea when removing the screws to lay them on top of a bit of stick tape
    and roughly in the same order or pattern that you take them out.
    Some screws will not be the same length as others.
    IMG_1647.jpg


    With the top removed this is the sight we are greeted with!
    Almost forgot to mention, just in case before opening.
    Stick a screwdriver and hold in place into the back of the gear box
    as shown when opening it. The spring is under pressure so can pop
    out fly across the room and take out your lovely LCD Telly or computer monitor etc
    so be careful. (or it may give a rather dis-appointing bend upwards and not fly anyplace)
    IMG_1648.jpg



    So what are the bits then!
    I've labelled a few on the pics below.
    IMG_1649.jpg
    IMG_1650.jpg
    IMG_1651.jpg
    IMG_1653.jpg



    Shims are used to adjust the height/positioning of the gears in the gearbox
    They can be applied both on top and under each gear.
    In a badly shimmed gearbox the gears will have a lot of up and down play in them.
    You need to be very careful with shimming, there are lots of guides out there about this
    aspect of things. (I'm still not 100% sure I know what I'm doing when it comes to this)

    If you adjust the height of one gear too much you may need to do the same
    to the other gears too.

    If you raise the height on your spur gear then you will need to raise the height
    of your bevel gear too.

    If you adjust the height too much on the bevel gear too much from under the gear
    it may cause issues when you put back in your motor with it not meshing together
    correctly. There is a screw on the bottom of the pistol grip on most
    AEG's (where the motor is in the grip) that allows you to adjust motor height slightly
    this may help if you shim your bevel gear slightly too high)
    Also if you raise your bevel gear too much your anti reversal latch
    may not align correctly and cause it to wear out faster than it should.

    If you don't have enough shimming on your sector gear it may interfere with your
    cut off lever and you will have firing issues.
    (I've not taken apart the cut off lever here as I did not need to)
    The cut off lever (sometimes called yaw control lever) sits right under the
    sector gear so you need to make sure this gear has enough clearance not to touch it.

    If you shim too much and you put your gearbox back together again it may put pressure
    on the gears and your motor might have a hard time turning them and cause issues.

    All sorts of gears too! with different ratios,
    and even modular gears that can be just popped in
    that are all perfectly matched and aligned.
    Modify_modular_gear.jpg


    Bushings.
    There come in different sizes, types and materials.
    The ones in this gun are Nylon and I think 7mm in size.
    These can be replaced with compatible metal ones if needed.
    If you do install new bushings make sure there are properly aligned
    and seated correctly. Some people also suggest these are glued in!!!
    as they may go loose and spin together with the gear after prolonged
    use rather than have the gear spin in them! For higher rate of fire
    set ups, metal bushings are probably better than nylon/plastic ones.
    Note: changing the bushings is not going to increase your rate of fire!
    but they will last a lot longer than cheap nasty plastic ones!!!
    I read someplace that Plastic Bushings should be replaced after about 15,000 rounds
    which sounds crazy since if you go through a bag of 3-4000 BB's and are a high capper
    per skirmish day that's not a whole lot.
    CA7mmbearings.jpg



    Anti reversal latch:
    This can be a pain in the ass to stay in when putting your gear box back together.
    You need to make sure its orientated correctly when installed and you need to be
    VERY VERY careful with the spring. The anti reversal latch makes sure your gears only
    turn one direction. If you ever get a gear box lock up where no parts have broken then
    this is the little thing you will need to release in order to reset your piston.
    (This can be done without opening the gearbox as you can access it with a pick
    by just removing the motor and pistol grip)


    I've left the trigger/contact assembly, the selector plate and cut of lever
    alone. They can be finicky to get back together and the contacts were not
    corroded or anything (I never used the gun in a skirmish ever)
    I have taken these apart before and had a small accident when assembling,
    the back of the trigger (as its low quality metal) where the spring goes
    into the hole broke!
    IMG_1652.jpg

    Next we have the other bits.
    Spring Guide is slightly different on V3 gearboxes
    but we wont worry since its a V2 were looking at here.
    you can get upgrades with washers/ball bearings etc that
    do different things but are not really needed unless your fussy.
    Ball bearing spring guide can aid spring rotation within the piston,
    if the piston also has a ball bearing and the spring is not statically
    attached. The idea being it causes less stress to the gears if
    both ends of the spring can rotate or spin??? (open to correction)
    Pistons come in all sorts of weird and wonderful flavors.
    Full metal teeth, half metal teeth, first few teeth metal.
    Low weight, high strength, super dooper material.
    Some people drill holes in pistons to make them lighter for high speed set
    ups.

    One problem sometimes is piston teeth can get stripped/shredded
    when there is a gun problem. People tend to think that full metal
    teeth pistons is a good solution for this.

    The problem then is you have to ask your self a question.

    If the Piston teeth don't break if your gun has a problem then something else or
    possibly several other parts may break instead! It would be better for a cheap part
    like a piston to break rather than having your more expensive gears get damaged or
    your motor burn out etc. Its all about balance and harmony! (I am guessing)

    Attached to the piston is the piston head. These also come in different types.
    You can get plastic or metal heads each with advantages and dis advantages,
    you can get silent head piston heads, ball bearing piston heads

    Piston heads have an O-ring around them which forms a seal when in the cylinder.
    They will sometimes have Holes on the face of the piston head. When the piston is
    traveling forward these holes allow air to go through the face of the piston head
    and its directed outwards around the o-ring causing it to expand and form a better seal
    for compression. There are 4 or 6 hole configurations and 8 hole configurations.
    Silent Piston heads have a rubber surface (along with a rubber surface on the cylinder head)
    They can help reduce noise a little but will reduce fps. Metal vs Plastic piston heads
    causes more debate on which is best but I've never experimented so don't know what
    the differences are.

    Cylinder. The one pictured is a Full cylinder.
    There are different types that can be used with different barrel lengths.
    For really long barrel's a non ported cylinder is used.
    For shorter barrels you might get a cylinder with a hole/port/slot cut in it.
    The position of this port can vary from the very back of the cylinder to towards the center.
    eg. if you change your barrel length you may need to change your cylinder to keep your FPS the same.


    Cylinder Head and Cylinder Nozzle also come with various bells and whistles like
    other parts, plastic vs metal, silent versions etc etc etc

    Nozzle. Make sure you use the correct nozzle (if your upgrading)
    A nozzle too long will cause mis-feeds.
    A nozzle too short will cause FPS drop.

    Tappet plate. There are different types of tappet plates but
    generally the same version gear box's use the same kind of tappet plate.
    The tappet plate pulls the air nozzle back to let the BB into the chamber.

    Spring, these can some teflon coated, stainless steel, linear or non linear,
    different lengths, different strengths. They can be free spinning in the piston
    or can be static and attached to the inside of the piston.

    So far I've been very long winded but I have been drinking lots of cider which tends
    to make me go on and on and on and on and talk rubbish.
    Since I only opened it up to change the spring and its open, may as well lube up.

    There are different types of lubrication you can get for your gearbox.
    I really don't know if that actually make a genuine difference or not or if they
    are a complete gimmick. (The most important and useful one is simple Silicone grease)
    Silicone grease was used to fix my real steel shotgun when ordinary grease and oil did not work
    its awesome stuff)
    IMG_1654.jpg


    The air-seal stuff I put rubbed with my finger on the piston head O-rings
    and inside of the cylinder.

    Black stuff when on the gears and red stuff went on the bushings.

    The silicone grease went on the piston, and the metal piston guides on the gearbox shell, as
    well as where the tappet plate moved back and forth.

    If your gonna play with a gear box the two things I would recommend getting after silicone grease
    would be some shims (which come in different thicknesses) and a gearbox spring set.
    One of my guns (An AUG) had a gear box lock up so I went to disengage the anti-reversal latch
    to release the piston from the locked position and I ended up accidentally destroying the
    very delicate spring that was on the latch. The guns sat their in pieces for weeks because
    I did not have this tiny tiny tiny little delicate spring to replace it with the one that I wrecked.
    a spare set of replacement springs cost about 4 Euros are are always handy to have just in case.

    IMG_1655.jpg
    springs_mtx_v2gb.jpg


  • Registered Users Posts: 4,612 ✭✭✭bullets


    Anyway stuck in the new spring and lubed everything up. Its important not to
    overly lubricate the gears etc if you dont have a hi-torque motor. (or so I've read)

    Onto re-assembly assuming you've played with the gear box and done whatever changes
    and shimming (and tested yer shimming of course...google a shimming guide)
    all all those wonderful things.

    The first gear I put in is the spur gear.
    IMG_1656.jpg


    Then the anti-reversal latch. Be careful this goes in the correct
    way around and be very careful with the spring. Also these never fit
    in snug in the hole they go into and have a horrid habit of popping out.
    Put a dap of silicone grease into the hole and it will help.
    IMG_1657.jpg


    I put in the bevel gear next(but others put in the sector gear next)
    making sure you pull back the anti-reversal latch so it engages the
    bottom of the bevel gear.
    IMG_1658.jpg


    I then pop in the sector gear. Make sure the teeth on this gear are
    facing down and have not engaged anything. Rule of thumb for people
    is the little notch/protrusion should be at the 1 or 2 O'Clock position.
    IMG_1659.jpg


    After this I pop the nozzle into the groove that's on the tappet plate.
    IMG_1660.jpg


    After putting the cylinder head (with lubed O-ring) into the cylinder
    it push fits! make sure the orientation of the cylinder head is correct.
    so the holes fit into the notches/pegs for them on the gear box shell.

    One thing to note here is you may push the cylinder head in too far or not far enough.
    You can adjust this as there should only be space for the correct length of cylinder and cylinder
    head combined, See the way the green arrow in the pic show the clearances in the shell.
    IMG_1661.jpg


    Piston and spring and guide can now go in.
    Make sure the guide rails on the shell are aligned with the guide grooves in the piston, and that
    the teeth on the piston will mesh up flat to the gears. (ie make sure its not crooked)
    Also make sure the tappet plate is sitting flat and moves back and fourth and that the nozzle is
    snugly still fitted where it should be (It can come off and you may not see it)
    Don't forget to add back in the tappet plate spring at this stage.
    IMG_1662.jpg


    Pop the top of the shell over everything making sure the bushings and shims are all in place.
    you may need to adjust one or two of the gear spindles with a screwdriver while holding the
    spring in place, the cylinder down, placing the gearbox shell over the top. Sounds like a lot!


    The gearbox can be eased back into the lower receiver now providing all the wires are ok.
    Be careful that the slot in the selector plate aligns with the cam in the inside of the receiver for
    the fire selector switch. (check by moving to all 3 positions after everything in place)
    IMG_1663.jpg


    At this point. Put the rear body pin back in to hold the gear box in place.
    Also put the pistol grip and motor back in, and the motor plate back on.
    Pop the pin above the trigger back in.
    IMG_1664.jpg


    STOP HERE!!!!!
    This is the point where you can test the mechanism to see if it cycles. attach a battery to the wires
    and test fire the gear box. If it works HAPPY DAYS! if it jams then you may have to open
    the gear box again to see what you did wrong.
    IMG_1665.jpg


    After this the mag release catch can go back in.
    Make sure the small screw on the button is fully screwed in.
    IMG_1666.jpg
    IMG_1667.jpg


    Stock can now go back on.
    IMG_1668.jpg

    The Barrel before we go any further is shown below.
    A good upgrade would be a tight-bore barrel.
    But be aware as well as increasing accuracy it will increase FPS so may cause
    a gun almost at the limit to go over. Also you may need to use high quality BB's
    as poor quality ones with loose tolerances may cause jams.
    IMG_1669.jpg


    The hop-up unit/chamber is shown here, its easy to disassemble.
    Just pop off those little spring washers and all the knobs and a pin
    come out. This will allow you to take the top plastic bit out and
    access the hop-up nub. (Note: if you take the barrel off first
    this nub will just fall out into the hop up chamber)
    IMG_1670.jpg


  • Registered Users Posts: 4,612 ✭✭✭bullets


    Here's a pic of it disassembled.
    IMG_1671.jpg



    The hopup Bucking rubber comes in different types/materials
    and different degrees of hardness. Hardness of rubber is measured on the Shore scale.
    http://en.wikipedia.org/wiki/Shore_durometer
    For a high powered gun I'm told that harder rubbers are used.
    For guns with a 1j Limit such as Ireland softer rubbers are more useful as an upgrade.
    The softer the rubber the shorter the lifespan of the hopup bucking.

    The Barrel has a little window in it. The bucking goes over the end of the barrel
    and when you adjust the hop dial it pushes on the nub which pushes on the bucking which
    protrudes through the window and into the barrel.

    When the BB passes through/past this is puts a back spin on the BB which increases the range.
    http://en.wikipedia.org/wiki/Hop-Up_%28Airsoft%29

    The Nub/spacer can come in different shapes.
    An interesting idea is Shredders Nub.
    Shredder's Concave Spacer :
    http://www.atlanticairsoft.org/showthread.php?t=3767
    IMG_1673.jpg


    The Hopup bucking itself is sometimes thicker inside at the particular spot
    where the nub pushes down and sometimes will have a lip/rise on the inside surface
    at this point. (beware of too much hop up, may cause jams in the barrel)
    Because of this region the hop up rubber/bucking needs to be orientated in a specific way.
    To aid in this there is a raised ridge at the bottom of the bucking which corresponds to
    a cut groove along the end of the barrel to endure it slides on correctly.
    IMG_1672.jpg

    On the barrel in the pic below you will see a spacer/spring to keep the barrel centered.
    Sometimes this comes with replacement hop up rubbers and is a Brass ring.
    (These can sometimes be incompatible with your gun) When everything is in place this
    spacer bit gets pushed into the hopup chamber section to make sure there is no barrel rubber.
    IMG_1672.jpg


    When putting the hopup unit back together again use a bit of silicone grease (wonderful stuff)
    so the nub sticks to the plastic bit as pictured in the center.
    (to stop it from getting installed incorrectly)
    IMG_1674.jpg


    Tip: Teflon tape as mentioned at the start.
    IMG_1675.jpg

    Getting back to the re-assembly.
    Barrel gets shoved back in.
    IMG_1676.jpg
    IMG_1677.jpg


    The upper receiver should slide back on but you may need to pull the inner barrel/hop up section
    out a little to get the wired pushed through the slot designed for them.
    IMG_1678.jpg

    front pin can go back in to lock the receiver in place.
    IMG_1679.jpg

    After that tis just a matter of sticking back yer battery wires onto the
    fuse/connectors and slap on the hand-guard.

    ~B


  • Registered Users Posts: 1,147 ✭✭✭THE MINDER


    Absolutely superb guide with crystal clear pictorial-well impressed Bullets:)


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  • Registered Users Posts: 426 ✭✭dinko4gr


    bullets the moment i read you thread i said WTH lets see whats wrong with this CA M4 that doesnt work. Followed all your steps to the letter and i just finished putting it back together. Guess what ITS FREAKING WORKING NOW !!!!:D the problem was that it was re-wired to the back to use a crane stock battery and for some weird reason the cables were a bit squashed so no power would flow to the motor. Now its working like a charm. Seriusly man all thumbs & toes up for you for taking the time to post this one. The only way that this could be done easier is if you were actually were here and doing it for me while i snored like a train :D

    If i may add a suggestion the most easy "extra" part of the M4 is the Bolt stop. You are lucky and its actually pinned to your lower receiver. On CA it simply comes off as soon as you remove the upper receiver.

    Im referring to this lill bugger :D

    Parts_GP832_lg.jpg


  • Registered Users Posts: 516 ✭✭✭robust


    Excellant job Bullets.
    One of the best hopup disassembly guides I've seen.
    Love to see some more.


  • Registered Users Posts: 1,222 ✭✭✭Irishmaster


    Great guide Bullets! Did you sort out the inconsistant fps problems in the end?


  • Registered Users Posts: 4,612 ✭✭✭bullets


    Great guide Bullets! Did you sort out the inconsistant fps problems in the end?

    Fires very consistently now :D
    only problem is its firing over the limit with the hop-up turned off :mad:
    despite me changing the stock spring,
    and cutting a few loops of the newer spring.

    There is still not something right
    Fires 249-255 with Hop up on fully.
    and unfortunately 340-350 with Hop up off.

    If I do something to knock 30fps off of it with hop up off
    then it will have a really be Low fps reading with hop-up on.
    (The stock bucking has got to be replaced yet)

    Springs are tough little buggers, I needed to take a dremel to it as there
    was no way my Tesco Snips was cutting through it.
    (Took about 2ish loops off of the spring which knocked about 15-20fps off of it)

    Rather than continue to cut more loops of the spring and needing to grind so sharp bits done catch I'll need to buy another spring much lower than a m100 or change or modify the cylinder to reduce the fps.

    When you start adding up the costs of new springs, bushings, buckings, gears, motors etc it quickly becomes more than the gun is worth.

    Since I don't use this gun, its gonna be a project gun or something to play with. I've been dying to try out these DIY water transfer Kits so might buy one next pay day and see how it works while I have this gun in pieces.

    ~B


  • Registered Users Posts: 3,152 ✭✭✭Inari


    What spring are you using? Are the barrel and hop rubber still stock?

    If you replace those two, the air seal should be far superior, and you can switch out for a lower powered spring, and keep the power up. Dropping 50 or so FPS with hop applied is typical of hard rubbers - if you switch to a soft bucking, then it won't be as dramatic.

    Personally I'd go with a G&G Green Hop up rubber, or Guarder Clear (I used to use Guarder Clear's exclusively, then I was forced to try G&G Green, and I've not looked back), with a JBU, Vanaras, Madbull or Prometheus barrel. Spring wise I'd say MS90 or MS85. If you go with the lower springs, and are a little low, you can replace spring guide with a metal bearing spring guide, which will bring you back up.

    PS: Very nice guide!


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  • Registered Users Posts: 4,612 ✭✭✭bullets


    Had a causality this morning the bolt stop broke in two when putting the gun back together again after cutting off a few loops of spring.
    Damn pot metal, not to worry though its only cosmetic.

    The Hop-up bucking and barrel are stock but planning on changing them.
    Its the hop-up rubber that is causing the inconsistencies when fully on.

    Its good to know that softer bucking will cause a less dramatic fps drop
    from fully off to fully on I was kinda going :eek: when seeing 90-100 fps differences.

    The replacement spring I knew was going to be a little too strong as it
    was a Deepfire 100m/s DF-CPS05 but it was the only one in stock in a shop
    when I passed by it while in town. (will pick up some bits and pieces this week to change out the bucking and get a new spring)

    I used the green G&G bucking on a different gun and it made a nice difference to range and I actually think the BB's fed a little better when I changed it. The brass ring/barrel space bit was incompatible with the gun I was using though.

    Here's what the cut spring looks like now, a lot shorter than stock.
    I'm now getting readings of 301-305 fps with no hopup.
    and 150-175 with hop up on. (varying a lot when hop-up is on)

    IMG_1687.jpg


    I was not 100% sure about bushing compatibility.
    Was planning on buying 7mm metal ones.
    Thought the nylon ones in it were 7mm and I see 7.03mm ones too
    so was not sure if that meant the hole in the gearbox where the inner diameter of the bushing sits (I presume its this) or the outer diameter of the whole bushing.

    Measuring the part of the bushing that sits in the hole:
    IMG_1689.jpg

    Measuring the outside of the bushing (outer rim)
    IMG_1690.jpg

    ~B


  • Registered Users Posts: 1,222 ✭✭✭Irishmaster


    PDI 120% springs are awesome and give exactly 1 joule in my g&g m4! Maybe try get one of them if you see them! :) I had inconsistant fps too with my m4, changed the cylinder head to an Ultimate one, pdi spring, now its shooting 320-328.


  • Registered Users Posts: 7,463 ✭✭✭Leftyflip


    Bullets - any 7mm bushings or bearings will fit in that shell without an issue. As for springs, the Guarder SP85's and SP90s are the best.


  • Registered Users Posts: 4,612 ✭✭✭bullets


    Still poking at this gun, I took the whole gearbox apart but I was at
    work at the time so could not take pics.

    Bought an Vanaras M90 spring & 5KU replacement gearbox shell as it came with 9mm Ball-bearing bushings, shims, springs and screws and boasted of being re-enforced.
    (Me thinks it may have only had a chrome spray finish on it though)

    Bloody nightmare of a thing. I was just about to give up and go back to the stock gearbox shell but finally (after MR Dremel paid a visit ) got it wedged in.

    The 9mm bushings were pretty nifty and after shimming (Made sure not to over shim) the gears were spinning very nicely.
    The hole where the safety lever bar /stopper bar (in front of the trigger area) was supposed to be was not present,
    after tapping around the area with a hammer I found it had some formed correctly when cast so a layer of metal had covered the hole. I was able to tap this out.

    The trigger contacts area would not fit in the new shell so I needed to cut away a little piece and enlarge a hold. On the old gearbox there was a metal pillar that held a screw in place for this area. The new gear box there was no pillar only a hole. Which meant the screw would not fit/reach.
    (and it did not come with longer screws I only had my original)

    All the holes in the gearbox shell that stock parts needed to go into needed to be enlarged.

    The selector plate would not fit it so the slots had to be filed with a blade, and the selector plate needed to be modified.

    Finally the gear box would not fit. It was wider by a 1-2 mm and longer by about a 1.5mm (maybe a little more) I needed to take the Dremel to some areas in the lower receiver and grind them down a little to get the new gearbox in. And needed to tape in the pins with a small hammer.

    Once in the the selector plate was pushing against the body so needed to file a bit off at certain areas. Its still extremely stiff but works.

    I also stuck a Green G&G hob up rubber in, and one of those fancy pants
    hand guards.

    Its firing 230fps with hop-up off (Thats a very Dramatic change)
    This drops to 215-217 with a hop up a little on.

    When I turn the hop-up to about 3/4 of the way the BB's start to jam so still need
    to look at this.

    IMG_1715.jpg

    ~B


  • Registered Users Posts: 1,050 ✭✭✭sci-ops


    I'm sure someone will disagree with this....and I don't have any fancy physics calculations/diagrams to back this up, however, try changing your cylinder to a ported one.....(Port at the rear of the cylinder)

    Any M4 I've ever worked on has had a ported cylinder. Tried non-ported cylinders in one or two and FPS always dropped dramatically. Replace with a ported one and whump, back up to 300's (with 85m/s spring)

    I was always under the impression that a non-ported cylinder was for longer barrel's eg:M16...something to do with volume of air etc etc etc.


  • Registered Users Posts: 1,147 ✭✭✭THE MINDER


    sci-ops wrote: »
    I'm sure someone will disagree with this....and I don't have any fancy physics calculations/diagrams to back this up, however, try changing your cylinder to a ported one.....(Port at the rear of the cylinder)

    Any M4 I've ever worked on has had a ported cylinder. Tried non-ported cylinders in one or two and FPS always dropped dramatically. Replace with a ported one and whump, back up to 300's (with 85m/s spring)

    I was always under the impression that a non-ported cylinder was for longer barrel's eg:M16...something to do with volume of air etc etc etc.

    I'll second that sci-ops.Through research,experimentation and experience I have found this to be true. Different manufacturers label cylinders differenty ie: systema call them Type0/Type 1/Type 2,3 and 4 -each corrosponds to that which will the balance the air volume of different cylinders to air volume of their respective barrels. Others call them A,B,C etc. There is slight variation in types recommended by different manufacturers but there is also some room for deviation in the type of cylinder used.The cylinder in bullets aeg would be considered to be 'TYPE 0' to be used (as sci-ops rightly points out) with barrels over 500mm in length(M16 etc).The M4A1 usually has about a 363mm barrel- Systema would recommend 'TYPE 2' but others their equivalent of 'TYPE 1' .Simply put-yes a ported cylinder Type 1 or 2 with M85/M90 (with a properly sealed cylinder/cylinder head/piston head and hop up) should produce 310-320ish FPS
    Some manufacturers are guilty of putting the 'TYPE 0' in everything-it is probabley cheaper to produce than a variation of ported versions for each aeg.
    Dave.


  • Registered Users Posts: 4,612 ✭✭✭bullets


    Cheers for the info guys appreciated.

    I had thought that porting a cylinder would have reduced the fps and not increased it. will give it a try. Planning on taking the gun skirmishing in the morning to see if it fires ok, and planning on sticking a tightbore into it at some stage so may pick up an cylinder too.

    Pretty interesting stuff playing about with things, a real shocker was a single tiny tiny tiny little shim is all it takes to jam up the gears when all screwes were tightened, and the pure frustration of stuff not fitting correctly.

    ~B


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