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Missfeeding and PME prevention.

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Hello guys,


I've been doing some teching for an year now for my friends noting major shimming re-greasing, compression upgrades AOE. This is the second time I've done 14:1, so I'm not that versed but want to get better. 


My idea was to make a sort of balance between the fastest trigger response I can get and have it reach reasonably far nothing too crazy.


Could you give some advice on a feeding issue. I have ELAR MARK 18 MOD1 (Platinum Version) bit of a mouthful but what  ewer. So I din't do my research properly and I'm kind paying for it now. 


So the rifle worked like a dream it needed some shimming but aside from that I was quite happy. It din't last long as the piston broke 4 Sunday skirmishes I replaced it with an SHS Full metal rack with 14 teeth, added bearings to it, did an ok shimming, re-greased it with ASG gear and cylinder grease and worked fine for another 2 games but then compression went to shit because the I didn't notice the cracks on the piston head. So I thought if I'm gonna open again I would do some upgrades. I had some parts lying around and the one peace cylinder was vary loose it had a lot of movement front to back in the GB, but I wanted the compression to last and get just a tiny bit of Joule creep as the limits in my country are 1.7 j with 0.3 g BBs for assault rifles, and there was a sale in gunfire, and the retro arms store so here is a list of the parts I replaced and what I modified to them.


Piston: https://gunfire.com/en/products/quantum-piston-with-titanium-covered-teeth-1152199541.html  sanded 3rd tooth for AOE. 

Piston head: https://www.retroarms.com/parts-of-gearbox/cnc-aluminum-piston-head-x used a bearing set instead of the plastic spacer that came with it.

Cylinder type C https://www.retroarms.com/parts-of-gearbox/cnc-stainless-steel to compensate for volume reduction from AOE Correction and have a bit more air volume for 0.32 BBs.

Cylinder head: https://www.patrolbase.co.uk/asg-ultimate-cylinder-head-v2 3 mm glued a silicone ring to accommodate a good AOE.

Gear set: https://www.taiwangun.com/en/gears/steel-14-1-highspeed-3-bearing-gear-set-big-dragon-golden-series?from=listing&campaign-id=19 could not find much info on the but a friend of mine has had the same set for an year now and it seems to work quite well with m110 spring I know they are cheapo but they seem to be holding up. I've also had it that set in a Specna Arms M4 for a 36 hour millsim event before the GB cracked and I gave up on it as it just didn't seem worth spending money and time on it. But I might have gotten lucky and made the perfect shim job but after I got them off they didn't even had a scratch on them.

Spring: https://www.torontoairsoft.com/SHS-AEG-Upgrade-Spring--M110_p_1335.html m110.

Tappet plate from an old G&G v2 as it seemed quite solid and seeing how durable E&L stock parts have been...

Nozzle: Stock just an o-ring change as the original was not sealing well

Did bevel to pinion shimming the stock pinion is not meshing amazingly but still runs very quiet and smooth will be replacing the pinion with Big Bragon or SHS to make it mesh the bast I can.

Installed a Perun plain micro mosfet I've installed about 10 of them so far had no issues had had one in my friends G&G that has the same gear set for a year now and 

All other parts are stock.


I worked fine with my guarder bluebox mags before the upgrade. I've used them on my ARP 556 and that does not have a sector delayer and shoots crazy fast for 18:1. And they worked great on The Specna Arms. 


So now I had to push the mags forward with some material at the back of the magwell. And I works but when the mags starts to get to around 30 BB's it starts to act up gain again. Compression is fine as well 1.4 j 90m/s with 0.30 BBs its pretty acurate and BB's are surprisingly fast to reach the target but that is when it wants to work.


So I'm wandering what might be the feeding issue as in theory the nozzle to hop up alignment should be the same maybe a fraction different as I didn't compare the thickness of the front of the tappet plates, I think  the G&G might be thicker but that would only mess up compression it should not affect feeding right?


Also I didn't know about Pre-engagement at the time. Would that be an issue I know the piston and piston head set is a bit on the heavy side and I'm worried it would be slowing down and pre-engage I'm thinking of Swiss Cheesing the piston to reduce some weight or just get an SHS lightweight piston as I was surprised and disappointed to see how easy the 3rd tooth on the modify piston shaved of when I was doing the AOE correction but would like to keep the piston head to have just that little bit of mass to it for the slight joule creep. Also would like not to short stroke as it would negate the whole idea of the build but if I have to I will also if getting a harder spring and cutting it down to get to the right fps along with the lightweight piston is an option that would ideal.


Sorry for the long post but I just wanted to be thorough as to give as much info as I can. 

Thanks in advance but any help would be appreciated.






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I thought I could type :D


The main thing you seem to be having is feeding issues

which is a big varied thing - especially on v2 compared to v3's

(V3's have a slightly bit more tappet/nozzle retraction than v2's)


read some of my crap here....




On a v3 you have say 11mm compared to 10mm on v2

Or at front of tappet at full retraction (2.5mm thick) you got 8.5mm Vs 7.5mm

Remember you need about 1mm to seal on bucking, 6mm to slip a BB through

leaves you with little margin on v2 tappet plate

see here:



So a v2 tappet retraction or the tappet "window" as I call it

the amount of retraction to chamber & feed a BB is less than on a v3 box - in general terms

So on a v2 you got to get everything checked as close to perfection as possible


Check retraction in TOP half of box, not with bottom half of box

actually check it in both halves, but the final retraction distance check in top half

(like thread showed - it is just more accurate)


On V2's if you use a slightly slightly too long nozzle you get great seal

but less space on retraction for a BB to slip in front of nozzle and chamber


If you use a slightly too short nozzle it feeds better but loses a bit of seal on bucking

so it blows at hop sealing and fps drops a bit


So it is so important to ensure the nozzle length is absolutely correct

and this window falls smack back in the centre

Just enough to seal perfectly on hop unit - different hops can effect this at times

but enough that nozzle itself is drawn back with over 6mm clearance in feed tube

It won't matter if you fit an enormous delay clip that holds the tappet back for 15 mins....

If there is only 5.5mm clearance in front of nozzle, it will never chamber a 5.95mm BB


What I would suggest to retract the tappet a tiny bit further is a delay clip

the round brass type, that has a tiny bit of material over the sector that will just retract tappet a tiny bit more


*** EDIT just seen your gear set ***


You CAN'T USE A DELAYER on that with bearing on sector gear etc...




so ignore the delay clip stuff as you can't really fit one


Buy a new SHS v2 tappet plate instead, sand front slightly maybe

but SHS tappet that should retract a smidge further is perhaps your best bet/option

(as you don't really the option of fitting a delay clip with those gears)


*** Rest of delay clip crap is left in for future reference only ***

(I don't like them bearing gear sets, prefer the tried & tested version of solid gears with delay option)


BUT you must check the tappet on full retraction that it does not bottom out out against cylinder head

(it shouldn't unless you use SHS tappets, they seem to retract a whisker more & with delay may bottom out)


see here....




NB: I have sanded front of tappet plate on SHS tappet coz it was a bit thicker at front

but the tappet fin would hit the axle of sector, so needed more modding so it returned 101% fully

(Again check all this final tappet retraction & return in both halves, but usually is more accurate checking in top half)


Now all this and more is a load of over the top crap for most people and not needed for most builds

if you stay within most moderate limits and ensure stuff replaced is properly checked for compatibility


But when you start pushing stuff, using other 3rd party parts then you need to pay closer attention

as well as try to anticipate & plan ahead to get the best possible efficiency on how all them parts work together


The other issue is mags and this can not be stressed enough....


Some mags are better/worse, some have stronger springs & others are weaker

The stronger spring mags will in theory have a better chance of feeding a BB to chamber into hop bucking


The next issue if the mags clips in and slightly shifts the M4 hop a tiny bit

some when they fit in some guns can shift the hop unit forward and you lose an airtight seal


Mid Caps, not always better than High Caps - usually as they have more strength in spring

but I have a few Mid Caps that the BB's got stuck in the mag as the BB's snaked through mag

For a while I was messing with hop bucking lips and delay stuff, when it was the BB's jamming in mag

not all other stuff I was messing around with, until I pulled the mag & saw two BB's wedged inside the mag

which was the real reason why it wasn't feeding - damn it, the poxy magazine was the issue not hop/nozzle

So try a number of mags including wind up High Caps etc....


You say the mags feed fine in ARP or other gun with 18:1 - but that is a DIFFERENT GUN, HOP, NOZZLE

plus that is running slower on 18:1 than 13 or 14:1 - you didn't say the rps or speed of guns in cycling


So at higher speeds, mags & tappet retraction have to be perfect


The other issue is hop rubber, the bucking lips...

you should be able to plop a BB into hop and push the BB through with a stick/screwdriver fairly easily

Sometimes if the bucking is squeezed into hop unit the lips get pinched and it becomes stiff to push a bb through

that will cause feeding issues, plus if the lips protrude too far they might show in hop feed tube which can fold over

and that will cause feed issues as the BB catches on bucking lip slightly showing in feed tube of hop unit


a good video showing hop/bucking issues is this:



What I'm saying is there are a NUMBER of reasons why feeding problems arise

and often it is not just one fix for all instances, could be one thing or a couple on another gun


On delay clips, people think longer delay is always better - not always the case

it is the tappet retraction distance that matters and different tappets and worn fins effect this too

also DSG's at silly speeds can't use big delay clips but can increase the retraction only but adding

a small thin sleeve on the sector's tappet lugs...

Those small brass sleeves that sometimes fit on some sectors & a few spur gears...

these are just under 3mm diameter, with a thin wall of about 0.6mm

they can carefully fitted on sector cam to increase final tappet retraction for DSG's

but you need to really check for tappet bottoming out on cylinder head at full retraction


So no massive large duration delay clips are not always the answer to feed problems

YES it may help but not so if wrong longer nozzle fitted eg: 5.5mm won't chamber a 6mm BB

(no matter how long it is delayed)

and it won't matter jack squat if your midcaps or mags are jamming inside or pinched bucking etc....


So feeding issues can be due to all sorts of reasons and impossible for me or others to diagnose

but can only give you a guide of what stuff to check and look out for

even then, we can still think it is something when in actual fact it is something else

(My own jamming Mid Cap for example despite all the planning & attention to detail)


As for PME, what rps and fps on 0.2's or whatever are you pushing

along with barrel length and I presume 11.1v is what you are using ???


Also until you sort out feeding issues you might wish to go easy on the speed

if you have a BB jam in barrel/bucking then that jam will slow piston return

and in that instance of piston slow return PME risk will greatly increase if BB is jammed

(if it isn't feeding/chambering at all there is not this risk but with a BB jam there is)


In UK with 350fps a respected 20~25rps is about the limit I would push a gun to

yes 30~35 is possible with Short Stroking but going really nuts at 40+ on a SSG will = PME


If you are using 400fps on 0.20's then maybe 30 rps would be my limit

or just below 35rps, but as always the faster you go the more wear & risk of PME

in general, I don't care how well it is built, the faster you go the faster it wears/breaks

(in general a well built 20rps will last longer than a well built 40rps by same tech is what I mean, like for like)


PS, I would have used a solid or cross bushing under spur gear as that is the one place

that some bearings (even ceramics) and soft bronzey G&G bushings can wear & fail in high stress builds...




Hope some of this stuff helps

it is not the gospel but some of the stuff I found to be of use to me over the years

NONE of this is set in stone, but some of the stuff I go with


best of luck

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Thank you very much! Very comprehensive. I have ordered Retroarms bushings and will be fitting them instead of the bearings they will only stay on the bevel that should slow down the gears a bit. Will do a test with the SHS Tappet if all fails I have one of those adjustable nozzles will try that as well. But as soon as I can find an SHS lightweight piston as it seems they just vanished from the sites I'm able to get deliveries I'll swap the modify piston.To reduce the weight bit and it should all balance out hopefully. I'll post results when I get it perfect.

And if I can find 14:1 SHS gears in the near future and these hold up till next maintenance GB opening I'll swap them.


Also have you ever used a Slog piston? As I can get one easier I i would just need to swiss it.



And yeah I forgot to mention the ARP is at 17 RPS have not tested my current setup as I was worried something might brake. And yes it is quite slower than what you say my setup might be.



Again thank you and will write again with odd stuff I come by any with this or any other builds.


Also I forgot I might try the original Tappet as well and check if the nozzle is sitting back far enough and also if something didn't go wrong with the bucking I even have some G&G blues that are similar to the E&L one H or what ever its called.


And I have a Retroarms hopup chamber on the way might give that a try it was for a different build but if it works it works and I'll leave it in this one.


Ok again Thanks a lot I'll report the results.

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Bearings are OK but if they are going to fail

it will very likely be that ONE under the spur/step gear


Some use all bearings, some use all bushings

or a 50/50 mix, but ensure under spur it is a bushing as it is smack in the middle of all the drive & stress


Just be personally I have started to use say a bearing under bevel gear, bushing on top

Spur/Step gear - bushing underneath, bearing on top like on Cyma box in pic

(where the Big Dragon cheapo gears from TG were a bit tight on spur so bearing reclaimed some slack)

Sector - either or all bushing/bearing or 50/50


Bearing under Bevel coz it spins 4.5 times to 6.25 times to rotate sector gear just once

so bevel is spinning loads so a bearing will help a bit, not on top as motor pinion can force bevel if too high

(shouldn't if you shimmed it correctly in the first place but gives it a bit of durability adjusting motor height)

Bearing allows it to spin better with less potential friction being generated in a dry bushing

yes the power/stress is there being transmitted a tiny bit but most wear is under spur


Spur spins about 1.5 times to a sector gear rotation - so no biggy if all bushing

or bearing on top if shimming space is a bit tight, but bushing underneath is most wise


Sector - really doesn't matter much, hardly spins in comparison to bevel etc....


End of day, each box & gear set will likely dictate what it shims up like

if bearings foul the selector plate, the play/space you have to work with inside

if anything like Cut Off Lever moves freely or impedes on a thick bushing inside etc....


So there is no written in stone rule that you must do this or that - just spur bushing is main consideration

and can confirm soft G&G bushings wear quickly under Spur gear. It is usually pretty worn after say 12 months

(But those bushings are as soft as cheese)


SHS pistons can often bind in a number of boxes

and I don't rate any of the 3 or 7 teeth pistons from SHS - plastic is a bit soft


Really don't worry about Swiss Cheesing a piston - honest

it is nearly a fucking waste of time unless you are really sad like me

An average metal rack piston on its own weighs about 16gms say

When you Swiss Cheese you are likely only to save about 10% or 20% tops if you go fucking nutz

So you will save 1.6gms to 3.2gms if you drill & file it to shit carefully without screwing it up

(or weaken it so much it just fails asap, and 20% is a LOT of material, really only about 2gms)

It isn't the swissing so much but the cleaning up afterwards removing all the strands of plastic

smoothing the holes & slots that takes the time

The bare piston weighs say 9gms & metal rack about 7gms so to save 2gms of plastic is going some

and/or there will be next to little left of piston if save 3gms and the time taken to clean it all up


No imho swiss cheesing a piston is not such a great & efficient idea considering the time do it well

You would be better off losing weight by dropping a bearing inside piston and running without it

or putting in a 20mm 5mm thick plastic spacer - that will save 3gms straight away without swiss shit

I've done it but I'm a sad git with time on my hands but really not a fantastic thing

plus you want some weight or mass or meat on piston to operate properly

(bit like very light 0.12 BBs travel less than 0.20 BB's - it has to have a bit of weight/mass)


Only for critical ultra High Speed setups would/should it be a possible consideration

or if your piston's total weight is say 30gms fully assembled with metal piston head etc...

Then you might want to bring it down to 20gms to 25gms

DSG's & mad mofo's might wish to get complete piston weight down to 15gms or so

but really for most builds 20 to mid 20's at 24gms or something is perfectly fine

(like I said 0.12's don't wok as effectively as 0.20's etc.. so optimum weight/mass)

So yeah Swiss Cheesing is not all it is cracked up to be imho or not often worth the time

(if you keep the weight reasonable to begin with)


At those sort of speeds of 17rps - oh jeez what are you worrying about PME

unless you are running say a m75 spring or something

PME won't occur in a m100 gun until you get into 20's and say long full auto bursts at 25rps +

(unless you get a bad jam and keep on firing & shredding stuff through ignorance)

but cycle speeds you are well within the margin of safety until 25~30 me thinks on say m120


Even if you upgrade motor....

(don't buy a SHS High Speed or 40k type motor - 30k tops I'd say with HS gears or 25k if using 11.1v)


TEST RPS on 7.4v first then multiply it by say 1.55 or 1.6 to get the expected 11.1v figure

So if shoots 19/20rps on a 25k motor 13:1 on 7.4v - then likely 30~32rps on 11.1v lipo

(not wise to push a UK gun 350fps on 11.1v with upgraded motor & gears past 25rps without more work)


but gives you an idea of margins and what to expect before you shred your box by taking the pi$$


Twenties is plenty for most users, be it std gears & fast motor, 13:1 & torquey motor

or maybe 11.1v on std setup to get near 20 rps

something around 20rps +/- a few rounds is quite decent without going real nuts and will last well

(without too much planning lightening PME worry etc....)


If you have an old tappet - the fin could be worn slightly so retracts less if knackered

A SHS tappet seems to retract a bit more than most - about 0.5mm but need to check as I said

(they are a bit more flexible than many stiffer tappets and often a bit bent - not at 90 degrees so just

straighten them in some hot/boiled water, sand front a little perhaps but SHS nozzles sit nice in them)


There are gears and there are gears at end of the day

sometimes I've found a SHS/RA set rolls better in a box & other times a BD or cheapo £10 set rolls better

but a cheapo set sometimes comes with a weak look bevel with narrow teeth

so on cheapo 13:1's with weak looking bevel I've used a good decent stock bevel that had more teeth width


pic says 1,000 words....




much thinner weaker looking 10 teeth on BD/ZCI cheapo set - nah not risking that

(16:1's seemed to come with beefier looking 6 latch bevel like SHS than weaker 8 latch bevel)


Some shit works better than others in some boxes and vice versa

Shimming is an art as each box is different and something you learn as you make more screw ups

(wisdom = wise after the event)

And as for shimming - truth be told I'm still learning more with each box I mess around with

plus if I wrote a post or guide on what moderate stuff I know it would take up the full bandwidth of forum


If you are really sad watch Rogers - Shut Up Gears on YouTube

way way way OTT but if most of us get a box shimmed half as good as then it ain't a bad shim job

way way too involved for most of us but really covers it in detail, don't 101% agree with everything

but covers it all in great (too much maybe) detail to assist with shimming up your gears


best of luck

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1 hour ago, Slaverius said:


Why russian?


Ever seen a russian novel? Forget killing spiders with one of those badboys you could beat a raccoon to death.

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Ok so.... I decided to change my pinion gear to an SHS one and see how it works with my non bearing 14:1 BD gear set. Soooo... its very bad. Matching the bawel and pinion seemed fine, but as soon as I started shiming the bawel to the pinion it became apparent that the teeth angles and the size of the SHS pinion it self is just bigger enough to be impossible to shim in my E&L V2 GB. But here is the worst part now the pinion is stuck it was a tight fit so I had to force it down the D Shaft (LOL) I shouldn't be laughing but now I cant get it out and the shaft started to come out as well.

Enough overtures heh! So the question is have I totally &*^%ED the motor or if I just carefully grind the pinion off it would be ok striking the old one and caring on with the motor as is. I will try to post some photos or do a video of how bad the shaft is moving, as soon as I can. It would be a great shame if the torquey boy m170 bit the dust it seemed besides the tanklike gearbox the motor was the only other saving grace of the gun, should have gone with a Specna and just getting a retroarms or some other brand gear box and a high torque motor and al the other upgrades and it puld have been cheaper not only the wallet. 

Again long post i tied to explain the sitch as short as I could. And thanks in advance.


Any help advice or what have you would be great. And if the worst come to worst how about 13:1 gears, and ASG U18000 for that "OK" trigger response with abit of power that I've been so despte to get without any fancy mosfets or selling my kidneys for an HPA, advice on brands for the gears besides SHS and where to get them would be appreciated and and any motor that would fit the criteria but again being more budget friendly as the ASG is pricy I get why but, but this setback will set me 2 months behind on getting ready for a big milsim event and getting that SSG A1 for it if my motor is kaput....

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2 hours ago, Slaverius said:

13:1 gears, and ASG U18000

I did 13:1 with the ASG U30K and removed 2 teeth from the sector. It's the E&L Ak2m4 gearbox so steel rack ect.

It's running bushings and a cut M110 spring.

With 7.4v lipo it's running 22rps no PME, Super snappy trigger response.


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