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so what do you think of this custom build for ak internals

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basically aiming for high speed good quality without going silly, and it will be going into my retro arms gear box shell with 6.01 madball 7075 aluminium barrel. the gun is a king arms ak47s marui shell with a 74 front end from a parts gun i had left over the only thing left to go inside is a mosfet and hop rubber which i was thinking modify flat hop and and flat nub

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I've never heard anybody saying how good Element bearings are, but I have heard plenty and have personal good experience with Kanzen. You don't have to go for their ceramic-uber ones, they do steel.


I would also choose a double O-ring piston head because, well greased, they can produce up to +30FPS compared to a standard piston head and O-ring. For a high cycle rate build you need lightweight, so this POM one is probably a better choice than the Magic Box or PPS aluminium designs. More compression means more FPS from a lighter main spring, which increases the trigger response and cycle rate, plus increases consistency between the power of shots which is better for accuracy.


I would also choose a POM delayer clip also, rather than the new steel one because, if you need to modify it to make it fit, it will be a lot easier to work. Although in this case it may well fit perfectly since you're choosing the same make of gears. Nonetheless, for future useability I would still choose plastic.


Don't forget grease. I use CT-2 silicone grease with Teflon.


If you are using a Madbull 6.01x455mm TBB then, even without a double O-ring piston head, you will have a hot gun: including an SHS nozzle* (which has an O-ring), then an M100 spring will give you about 385-90FPS, possibly a fraction higher. If I were you I would get the double O-ring head and both M85 and M90 springs with a 6.03x455mm TBB and see which spring works best.

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Dunno if you are putting any gears of what type in there

but that length barrel 6.01 might be too hot & too tight - jamming if less that brill ammo used


Could always just buy a cheap cyma 028 box and a few little tweaks + ya motor & fet etc....

(o-ring nozzle, check seal on piston/cylinder, AOE, time doing the shimming - be a cracking little box)

then add fet + deans + motor to improve rof & response - 6.03 barrel probably best all round option

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Oops, I forgot why i put that asterisk above...


*I don't know which length of SHS nozzle you would need for an SHS hop chamber in a KA TM compatible receiver. I'm pretty sure that even the shorter SHS one is 20.5mm long which is about 1mm longer than a TM AK nozzle. There is an ACM aluminium nozzle with O-ring which is 19.5mm long - u can get it from taiwangun.com here (even though they advertise it as 19mm). I've just ordered one of these from gunfire.pl just so i can measure it, because i already have a spare one of those from taiwangun for my new RPK (which I also will be modifying for fast cycle rate), so on Thursday when it arrives I'll be able to tell you exactly how long it is, if you're interested.


TBH i'm not sure why the difference between the various lengths of 'short' type AK nozzles makes any difference, especially when you have a delayer clip fitted, because surely so long as it makes good contact with the hop rubber, it doesn't matter if the tappet plate spring is pushing it slightly harder forward. Perhaps someone has an idea? Because I have had problems trying to get a replacement Lonex nozzle, rubber, and hop chamber in a CYMA AK to work together and the fix was to change the nozzle to a 19.5mm one, the same as the original CYMA.

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get box sorted - firing well good seals etc...

(even standard parts if fitted and running well will bring good improvements)


then when setup well you can just wire in a mosfet without needing to open box back up on a v3

and see the improved rof & response.


Out of interest what rate are you seeking coz tbh a high rof is great but if you want it to last longer

then run on sensible volts and still get great rof on a 7.4v

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Cool the gears are 14.1 shs super shooter gears if that was not clear as of rate of fire i am not actually sure, i wanted a good rate of fire from a low volt battery rather then having to use 11.1 lipo the cylinder is also a single piece cylinder and cylinder head cncd from one piece of metal so there is no need for a cylinder head and i choose both long and short air nozzels because i have no idea what i would need but i take it you guys think that apart from tge bushings everything should go well

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I should point out as well currently there is no gearbox and it is being built from scratch


in that case maybe get a cyma gearbox or just use stock gears - what !!!

yes stock gears 18:1 with shs high speed all rewired with deans & a basic fet will greatly improve rof & response


You need to crack open the box and check shims/regrease/ensure seals are good fit o-ring nozzle

most of all you MUST check/do Angle Of Engagement unless you like piston's initial tooth snapped off

Tiny slits near back or port quite far back for 455mm barrel I reckon


Check box/seals work fine all fps looking good first...


Then add shs hi speed - considerable increase on its own

pop in fet on old stock wiring at trigger wires - new motor & battery wire on 16awg with deans

Now test her on stock gears.....


7.4v lipo 25c = 19 to 20 rps

9.9v life battery 25 to 26

11.1v lipo battery 30 to 31rps


Pretty impressive for old stock gears- however watch yourself on 11.1v lipo's & approaching 30+

If your piston is quite heavy/weighty on a stock m100 spring it won't return quite as quick as a light piston if

this happens at higher speed PE or Pre Engagement can take place - on all metal gears on piston

There will be no weak point to break and one hell of a BANG can happen if everything is all metal


Reason of the PE warning is coz if you run with M100 spring or less it is more likely to happen

People in US can use M110 - M120+ which will return heavier pistons faster & avoid PE

When peeps build very high speed setups they get the weight right down to 10gms by swiss cheese oh high rof & DSG's

All metal teeth, piston bearings etc.., add extra weight from 20gms to 31gms

or you could get a complete piston with 1 metal tooth at about 16gms without swiss cheese


Or you may need to run a higher spring - taking you over 350 but short stroke it to bring you back down

But as long as you don't go mad and stick to 20 to 25rps then PE should not be a possible worry


People think you gotta have high speed gears for higher rof - you don't

You do need a higher torque motor to turn higher speed gears or a stronger spring -M130 on DMR's say

But not all torque motors turn quickly - some are not much faster than stock but are much more powerful

Some torque's are quite quick - but not all of them.


SHS High Speed is a bloody quick impressive cheap motor especially when dean/fet/16awg is done

Then you really unleash the potential of it and will turn as quickly as you can supply the juice to it

People say torque is better - you are using a stock or lower than stock spring and stock 18:1 gears

the motor is not having to do any extra strain except run quicker which it will

You could just use deans but you should use thicker 16awg coz the stock motor wire will get very warm

AND fit a basic mosfet to avoid contacts arcing/burning out


You don't need an Active Braking mosfet - it won't double fire on stock gears and the stronger neodym high speed

motor will come to rest very quickly anyway once power is cut - stock motor's (ferrite) will roll on a bit but neodym won't


Get a half decent cheap box - say £40

check it works reasonable ok - probably too hot with a m120 spring in there


Then buy a m100 or m95 spring, piston o-ring, o-ring nozzle, some cheapo self adhesive washers to do AOE

PTFE tape to seal cylinder head, shims grease etc...... - £10 to say £15

Maybe better double o-ring cylinder head, steel/ali cylinder instead of brass type if you want it running best seals

(imho - perhaps lose piston bearing it adds weight to piston and if not installed with loctite they often come undone

use a lighter plastic spacer/bushing if buying a new piston head but stock might be ok but fit a bearing spring guide)


Make sure all bits turn and slide real smooth and work all ok...

Test it all out - job done........

(buy a load of various parts to build a box from scratch and they may not all fit/work correctly together straight away)


Do the wiring & mosfet once the box is running nice and quiet with good seals etc.. like I said


I am NOT an expert - far far from it I am still learning (and breaking stuff though not so much as I was at first)


However I have read/researched a lot of stuff and one of the best guides on what you seek is here:




It has saved me probably about 12 to 24 months in major headaches & busted boxes and mega mega kudos

to the guy for putting together such a comprehensive guide all broken down in various stages of tuning

and what you need to do to obtain an increased rate of fire


Final thing - insane rof & DSG's etc... - just means in general ya box will crap out quicker

it is like a car - faster you drive it at higher speeds in your box more heat/wear will occur

the more miles or shots the quicker your car/box will need servicing


With that "general" common sense bit out of way - do the stuff above without going too nutz

keep the volts low and she will perform well for longer plus 7.4v lipo's should be cheaper/smaller

and you will see a vast improvement over a stock gun without needing to spend out too much

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SD, you've done it again, mate. My guess is that, unless someone already knows what you are talking about, less than a 1/3rd of what you've just said makes enough sense for people to take useful advice from it.


As i understood the OP, he already has a V3 gearbox shell and is proposing to fill it with the parts listed in order to create a reasonably high cycle speed gearbox, without spending silly money, but also spending what it costs to be sure of decent quality. I'd say you're on the right track in the main, Chris, but just be aware that an M100 spring combined with a 6.01x455mm barrel will give you an AEG which is too hot to use on full auto anywhere in the UK. As a general rule 6.01mm is too tight for guns which you are intending to run with full-auto capability, fulfilling the assault rifle role, anyway, because you are probably going to want to use just averagely good ammo - Blaster 0.25g for eg.


Predicting final FPS from a combination of upgrade parts is a bit of a black art, but really for us to advise you on the combinations to consider we need to know what FPS limit you are aiming to be under. Again as a general rule though, 6.03mm is the way to go for a 455mm long barrel in an assault rifle. I run a 6.02x275mm in my AKS-74U on full auto, firing mainly Blaster 0.25g BB's, and i've never had a jam. I suspect that you'd be ok with 6.02x455mm, but that would tend to make the calculations a bit of a pain in the hole.


If you are intending to use it at sites with a 350FPS limit then, with the parts list you have above, an M95 spring and a 6.03x455mm TBB should chrono at about 345-48. But as I said above, I would choose the double O-ring piston head and an M85 spring, and be prepared to find some tubing to use as a grommet to pre-tension the spring a little if you end up chrono-ing as low as 342, maybe an M90 and be prepared to clip a couple of turns off it if you end up slightly over 350...

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I was taking no gearbox and being built from scratch


Whilst he buys up lots of bits n hope they all work together OK....


Was saying get a decent working one and just a small tweak here n there will do same job


Yes I went way way overboard but everybody says high speed gears n high torque I'd way to go...


Nope the link demonstrates it is not a must particularly if keeping fps to UK specs...


Sounds daft but really can get great performance without all the extra high speed gears putting more stress on motor which isn't designed for higher gearing or pulling higher springs...


High speed and stock gears do produce good results as link shows

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some very good advice sitting duck and i have taken it on board especially the part about the mosfet wiring and deans. but ian is dead on the money the retro arms gearbox is already bought and i intend to fill it with good parts without breaking the bank. i am actually aiming for about 350 fps i am actually pleased i can use a weaker spring as it means less wear and tear on my gears and motor, i actually thought the spring might not be powerful enough, thankfully the retro arms box is built for quick spring change which i assume means i don't have to take it all apart again to change the spring. Also the element switch comes with silver plated wire i always though this could carry a high current but without the fitting problems of 14 awg or should i cut it off and replace with 14 awg. are you also telling me that the 14.1 gear ratio will burn out my motor and i would be better off with 18.1 gears because i do have the super shooter gears in a higher ratio in my m4 not doing anything if i need them

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Oh I agree with you SD, it's just that to someone who doesn't already know the arguments/considerations for the various ways of doing things, the way you wrote it was pretty impenetrable :lol:


That's another reason for concentrating on maximum compression - by allowing the use of weaker main springs your motor is under much less strain, whatever gearset you choose. Yeah, a weaker spring increases the likelihood of pre-engagement, but even using 14:1 gears and an SHS high speed motor (which does have the power handling necessary to pull springs up to M110 via high speed gears without running out of sheer torque and slowing down as a result) you'd have to be running high voltage before you reached rates of fire where that could become an issue.


As you say, SD, a MOSFET is also the way forward, for all sorts of reasons, but specifically in this case so that the power of, say, a Turnigy Nano Tech 25-50C 7.4V LiPo* can be delivered instantaneously to the motor so the initial few milliseconds of trigger response are not compromised by the additional power requirement to get a higher stress set up like this moving from its static position.


*From hobbyking.com (if you don't find the shape you need under that link, look in the menu on the left under Batteries & Accessories > airsoft Batteries) / the sustained output of 25C is more capacity than full auto fire would generally need, but excess capacity improves trigger response anyway, however what makes these batteries so good for airsoft and in particular for fast trigger response is their burst output of 50C: ie they are capable of delivering a lot more power for the initial few milliseconds when the trigger is pulled than most LiPo's available from airsoft suppliers; it is these first few milliseconds that really count for trigger response, because to get any motor moving from static requires a great deal more current than it does to keep them running - a decent airsoft motor actually draws more current than an electric cooker very briefly, assuming the wiring and connectors can handle it.


As SD says, rewiring with fat wire is also a must - these days i've stopped buying expensive silicone insulated 16AWG wire, or Modify silver plated low resistance wire, in favour of plain old Maplin power cable - the diameter of conductor is sufficient, the insulation is more robust, and it's a lot cheaper. I've also gone in for plenty of heat shrink - additional layers over parts of the wire susceptible to being crushed between the gearbox and receiver for eg, not just covering the soldered ends. Also there is a small but noticeable power increase from soldering the connections to the motor rather than using spade connectors.

Edited by Ian_Gere
clarification of whom i was speaking to
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If you get silver plated lo-res wiring with the switch, may as well use it. 14AWG is probably a fraction better, but it does introduce a few problems due to getting jammed in the spaces available for wiring. 16AWG is good enough, IMO, but as i just said, lo-res is lo-res, so if you have it, may as well use it.

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18:1 to 14:1 = aprox further 28% increase in rof

I say aprox btw, might be a tiny bit less due to very slight increase in tension/gearing so say 25%


if you stay on 7.4v you will should be fine

if using 9.9v life then it may get closer with an additional quarter increase

eg: 25rof on 18:1 top speed then 14:1 could be over 31rps


again there is a "possible risk" of PE at higher speeds is all I am saying


The reason for just using a decent "normal box" is Mr Monkey Nutz had a nightmare

with his QD box build from scratch, tappet/nozzle losing pressure etc....

That was all

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Don't get me wrong - good quality parts are miles better than most stock parts

Good SHS gears, better cylinders than cheap brass types, double o-ring cylinder heads etc....


Most of the time they will fit together very well and operate real smoothly

But on occasions the tappet plate/nozzle/hop up bucking may not quite make a perfect seal

and you can lose fps - on the expected performance - like Ian the AK man said about different nozzles etc...


The bitch bit is with a brand new build if bits are not quite a perfect fit you can't compare old nozzle length/tappet etc.....

So it became a bit of a bitch trying other parts and double checking stuff for Mr Monkey Nutz


But usually most good TM parts work very well together and may only need a little check and tweak when assembling

(all part of the "fun") and is where your skills and patience can be tested

Getting a working box and adding a few upgrades is relatively straight forward - pah I can do that


I'm sure it will all be fine sir - if you run into problems there are some very experienced people on here

(not me - I'm thick as 2 planks)


The link is a very good read though from some very clever mofo who knows a LOT more than I ever will about high rof

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I'd recommend the madbull steel bull barrels, i haz one and they're rock solid and perform well. I've never used a madbull aluminium barrel but steel is more durable than aluminium so go for that. They are pretty hefty though, i have a 229mm version and it weighs more than my metal handguard

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Yeah, the issue with the durability of the materials used to make barrels is not how strong they are really - i mean if you abuse your gun so much that the inner barrel is in danger of being bent, there are many more expensive parts which will fail first so you'd have bigger fish to fry. The issue is how well the inner surface withstands normal wear from BB's being fired through it and the unpredictable effect of dust particulates abrading it, plus the potential for scratches when you clean the barrel as dust particulates get trapped by your cleaning wad and dragged up and down the barrel as you work it up and down with your cleaning rod.


Chrome plating produces the hardest inner surface, followed by stainless steel, then coated aluminium, brass, aluminium, copper.

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the barrel is made out of aircraft grade aluminium tho ak frazzle so i have no worry s about its strength and here is a video of 7075 gearbox being smashed with a hammer to prove my point https://www.youtube.com/watch?v=9U1-RGmLGAQ

A barrel is much thinner and longer than a gearbox and bends more easily. Also because it's stainless steel, the insides wear out slower and is less susceptible to scratching.


Anyway, just go with whatever, the steel bull isn't much more expensive anyway.


One more thing, tis frizzle.

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