Krytac & 13:1 Gearset

[richmt11]

Holla Ballers,

hope everyone one is doing well?

i just finished my work on the Krytac and just wanna check a couple of things before I move to the next step.

so after much grinding I’ve got the SHS 13:1 gearset and Titan mosfet in my Krytac. Coupling this with an M120 and short stroking. And it’s rapid! (Feels that way to me).

anyway stock 20k Motor gets super hot after around 50 shots and will soon lockup. Let it cool and it’s good again. So before my next game day just wanna check it’s just down to the stock motor, putting in an shs high torque will sort this?

the gearbox is nice and smooth so I’m sure it’s just the motors not up to the job? I was hoping to get a game out of it as I have to stage my purchases so the finance manager of the house doesn’t complain!

also it misfeeds every 3rd shot or so (even in semi). I have read something about the SHS nozzles being longer? Is this confirmed? I just need to seemed some down and tidy it up?

i only play semi so mostly building this for trigger response.

cheers

rich

 

[Sitting Duck]

SHS nozzles are 21.45mm

Compare or measure stock Krytac

Always double check stuff you replace

(101% TM compatible is a myth at times)

Failing that go back to stock nozzle

stuff getting warm/hot "could" be down to ab on Titan

Or

Bevel to pinion shimming out

quite likely, get a RC Power meter and fire auto for 4 secs noting amps

If you are much over 15amps on 13:1 SS with 20k motor then shimming is out imho

(based on similar builds)

How many teeth did you remove on m120 - perhaps 3

What juice are you running on the 20k Krytac - 11.1v ?

(SHS HT is a 28k to 30k motor so will be going much faster that 20k)

Sounds like Titan is noticing high amps and shutting down

not expert on Titan - ask Hangtight but think it can shutdown on overheat/high amp draw

Which I suspect is down to shimming tbh,

could be a bit of both shimming and AB, but shimming is out anyway I'd say

How fast is the gun cycling, 11.1v, 20k motor - say 25rps or 16.5rps on 7.4v

Asking the daft question, not your mag is it ???

But lemme get this straight....

You took a Krytac with a 3034 already installed

put in a 13:1 SS with m120 which should prevent any overspin

Then ripped out the Krytac 3034 and put in a Titan to play on semi only ???

I mean it is totally up to you - your gun

Titan will give you bells/whistles, pre-cocking etc...

But as I say to each their own

check ya amps/shimming

 

[richmt11]

Cheers I’ll check this out. The gears feel nice and spin up well when everything is out, but could be that I need to tidy up the spur gear from the grinding, and will check my bevel again.

i think I can check amps in the Titan software? Or put my multimeter in line set on dc current?

to be honest I wanted the bells and whistles, so I brought the Titan and it wasn’t until last weekend when I’d got the grinding done and put it in. When following instructions to checking sensors I realised they want another £30 for those bells and whistles. So I feel proper ripped off by them. But now I’m down that road I have to follow it to the end...

i am happy though to have the short trigger pull. And will eventually “upgrade” to get the precocking.

 

[richmt11]

Sorry I didn’t answer the questions you posed. Wife’s out and kids are suddenly decided they’ve got a million questions.

ive got a 7.4v at the moment as that’s what I got because the Krytac sticker said not to use 11.1v. I’ll plan to go to that but just gradually putting it together.

could be the mag they are cheap mid caps so I will load up the Krytac hi cap and wind it right up first. I just remember reading somewhere regarding the nozzle length

 

[Hangtight]

Check the average and peak current draw in the Gate app. As long as everything is running well there shouldn't be any reason for the Titan temperature to get over around 60°,even on rapid semi auto fire. If the temp is good on the Titan but the motor is getting hot then the motor is overloaded. 50 or so rapid semi shots at 350 fps/13:1 is going to be enough to get the stock motor warm/ hot, probably enough to feel through the grip, but that's it.

 

[Sitting Duck]

Sorry I didn’t answer the questions you posed. Wife’s out and kids are suddenly decided they’ve got a million questions.

ive got a 7.4v at the moment as that’s what I got because the Krytac sticker said not to use 11.1v. I’ll plan to go to that but just gradually putting it together.

could be the mag they are cheap mid caps so I will load up the Krytac hi cap and wind it right up first. I just remember reading somewhere regarding the nozzle length

Oddly enough you could have used 11.1v on a 20k motor....

When first batches of Krytac came over they used the 30k motor

but UK spec was a m95/100 spring to get 330fps

So 11.1v on 30k motor with light spring is going some

So on this setup you would have got potentianl double fire on semi from large overspin

Or on really bad case scenario risk of PME with high burst 35c/40c 11.1v mofo

Krytac made the 20k motor for markets outside the US due to lower spring guns

rather than the 400fps/higher spring guns etc.....

(Well something like that according to Krytac's Allizard tech bloke)

If you got a grey/gray US import or early Krytac with 30k then you should use 7.4v

Hence they stuck on the 11.1v warning to limit new owners wrecking stuff on UK spec guns

If you think about it it is same meat different gravy....

20k to 30k is a 50% increase aprox

same as

7.4v to 11.1v is again 50% or 2 cell to 3 cell increase

So a 20k with 11.1v is about the same as 30k on 7.4v (roughly)

(under load higher speed motors lose a bit more top rpm than torquey motors etc...)

But the two examples were a rough similar output in real terms

Krytac stuck the 11.1v warning to cover their ar$e basically should a 30k slip through

the 3034 mosfet will handle 11.1v & 14.8v, it was just to do with rps on low spring & PME risk

Even on a 30k, you could be ok-ish on 11.1v 15c or 20c but above 20c you are going some

slap in a 35c+ and it will give you extra zest compared to 15c and get closer to PME risk

coupled with general noob error of clearling jammed gun by going nutz on auto

(yeah Krytac thought they best tame lower powered guns a little)

ROUGHLY speaking UK spec guns 20rps no problem

At about 25rps you will get more overspin and odd double firing

(I'm talking on non AB guns btw)

Above 25rps then things get a tad riskier as m100 = slower return piston

Compared to m120 faster/powerful spring returning piston at full stroke blah x 3

I say ROUGHLY coz PDW MP5k's will have say m105/m110 to hit 330fps

And long AK's will have m95 & hit 350fps - so it varies a little on gun/barrel/creep

But roughly speaking your std Krytac with 20k was hitting say 14/15rps on 7.4v

So by slapping in 11.1v you would have got 21/22.5rps

Or

Just put in a 30k motor on 7.4v and got about 20/21rps on 7.4v on the std 18:1 gear set

Whoa - long War & Peace novel again......

Your amps are too high coz bevel is shimmed too low/tight to pinion (most likely)

Use less shims on top of SHS bevel coz it is being pressed hard against the box....

First pic the bevel has too much shimming on top so it stays low

pinion can't get into mesh nicely with full teeth contact and is ramming it up against box

THIS is where all the strain/load/friction is coming from (or most of it)

Massive increase in load = muchas ampos & grande scorchio

(I mean yeah in rare examples the bevel is too high and pinion tip hits the AR Latch lugs on bevel)

Hence the bevel to pinion height is rather critical foundation to how efficiently the box/gun runs

What you could have done perhaps.....

Used Krytac's 4 lug bevel gear with SHS sector & spur and you "might" have had more success

(provided you didn't alter the original shimming on bevel)

Then shimmed up the 13:1 spur/sector and checked they meshed OK with original bevel

(should have, though there might have been a tiny roll back on 4 latch Vs 6 latch on SHS)

At least that way, it was more likely not to develop overheating from bad shimming on new bevel

(well in theory)

Check your amps

watch some shimming tutorials

(you can watch "Rogers - shut up gears" but really way OTT tbh, but a good understanding of crap)

I very much doubt as a ROUGH guide you need more than....

0.2mm on 8mm bushings

Or

0.35mm/0.4mm on 8mm bearings

BUT EVERY BOX IS DIFFERENT !!!!!

Some bushings can sit lower than most others - SHS "regular" bushings are fat bastids

(but they do thinner black enhanced bushings too)

Ceramic bearings are also fatter than regular 8mm bearings too

So you can't just think "Oh that will do....."

You have to check all this crap yourself coz each box is different etc.....

Also a 6mm bushing v3 and just recently a split v2 ICS 7mm bushing was 0.6mm on bevel gear !!!

So take what I said as a ROUGH GUIDE with a pinch/bag of salt

Also different bevels have the teeth cut lower/higher compared to others....

see middle bevel in here in this extreme example....

So every time you change stuff, especially the bevel and also motor/pinion too

(again some pinions/motor teeth are fatter/thinner or cut differently/flared/angle etc...)

Every time you change stuff in that area, the shimming & motor height will need checking

Well if you want your gun to run as smooth/cool/efficiently as possible

(your hot running gun is also robbing you of final rps from the strain/load/heat btw)

Best of luck - soz for epic waffle, there is a shorter 3 part trilogy film coming out later in year

PS

The KRYTAC air nozzle measures approximately 21.13mm in length, +/- 0.02mm

(ICS M4 nozzles are 21mm, so in some builds the SHS 21.45mm is a smidge too long)

If the std Krytac is not too loose just put that on

or file the Red SHS one CAREFULLY SQUARE/STRAIGHT a smidge if you wish

A delayer could help, but you might be a tiny bit tight for a 6mm bb to just slip past/feed

Easiest thing, is to use original stuff if it works ok and not too loose/worn

the slight leak is very very slight as most of air is being forced forwards

So unless it is very loose or damaged use old nozzle perhaps

Or file away the red paint at tip of SHS one straight and smooth

perhaps a delay clip.....

I often use these...

https://www.ak2m4.co.uk/internal-parts/gears/zci-gear-delayer

BUT they do retract the tappet/nozzle about 0.5mm further

so yup they can help with feeding....

BUT you have to be careful the back of tappet/nozzle doesn't bottom out on cylinder head

(especially with SHS tappet plates, as they also retract a whisker further)

If stuff bottoms out on cylinder head, or even on spur gears shaft or hits back of box...

(bit odd putting a Lonex type tappet in G&G but is really to show stuff bend/breaks)

Poxy gun crap - not quite as straight forward this teching crap as we all first thought

You spend a LOT more time checking crap than we ever first imgagined

This TM compatible stuff is often a bit of a myth.....

Best of luck

 

[Davegolf]

Whoa sittingduck how do you do it, you must have calluses on your fingertips

 

[Sitting Duck]

Whoa sittingduck how do you do it, you must have calluses on your fingertips

I don't get out much

but it gives me a chance to act the jack a$$ too

OP still has a shimming issue with his SHS gears

but they are OK gears as we know - they have been approved by 007 himself...

 

[richmt11]

:blink:  thanks...

lol, no seriously thanks for the information!

i did last night restrip the gun and found some chipping around the part where the pinion comes through. So like your picture as it’s set back due to over shimming it’s rubbed on the gearbox house. Although it didn’t make any noise to indicate that it sounded nice, just getting hot.

i think I’ll refit the original nozzle, it was ok. But the only part I changed as that’s the only part that leaked slightly in that assembly. But I’ll switch it back.

im glad to hear you say I can use the original bevel as it seems I can’t get the SHS bevel shimmed 100% correctly due to it being much fatter, so I was thinking about buying some bushes to give me something I can grind down if I need to. But now you’ve said about using the original bevel, I did put the original bevel in last night with the new gears and checked it’s still around 13:1, so was hoping that would work.

thanks for you taking he time this far, I know it can get tedious when noobs come in wanting to upgrade their guns (in the way I’ve done) when simple improvements could yield the same results! For myself I must admit the Krytac is an absolutely fine gun out of the box, I’ve not really even had any feelings of needing it better yet if I’m honest. But two things, it’s like getting a Ferrari you can’t drive that fast on the public roads anyway but it’s nice to have it in your back pocket Ready. And the second thing is I’m an engineer by trade so taking things apart and tinkering is genuinely fun for me. I never put all this stuff in because I want to show off or anything I just like playing 

 

[Sitting Duck]

It's all a learning curve m8

Most of us on here have a bit of wisdom from work/cars/diy etc....

But these poxy toy guns are not quite so straight forward as we are first lead to think

Just like the nozzle less than 0.3mm - so what's the big deal, ergh it can matter

plus slap replacement stuff together from ultra fine precision places knocked out from China

(no wonder some upgrades badly assembled make matters much worse - done that plenty times)

I'm no expert - far from it

I have made so many balls ups & learnt from these mistakes

(wisdom or wise after the event)

live & learn, but in the end like most crap in life

the more attention to detail, constantly checking everything you upgrade/replace

all that will work wonders - digital caliper to measure shims & nozzles & tolerances

Stuff like that, then the rest is just down to experience or learning from mistakes

(I'm still learning with every box or gun almost, broke loads taking the pi$$ - yup we've all done it)

You can drop a SHS or RA High Torque in there and hit say around 24rps on 7.4v

but this shimming, bevel pinion, motor angle and all that crap is vital for smooth efficiency

Stops extra strain, amps (drains battery much quicker), extra heat & sounds like cat being stung by wasps

Can still sound a bit shrilly on some bevels/pinions but hopefully lower noise/stress/friction/amps etc....

You'll sort it I'm sure, trial & error & learning from experience etc....

Often we rip a box open to make a slight tweak here n there

It doesn't always go perfectly to plan first time even with loads of care & attention

I did put the original bevel in last night with the new gears and checked it’s still around 13:1, so was hoping that would work

Most bevel's have 10 teeth that mesh to spur gear

So the ratio doesn't alter unless you use a bevel with more/less teeth

(there are 8, 9 10 is in 98% of gear sets, 11 is rare & 12 is extremely rare)

Ratio changes mostly by the spur/sector gear arrangement (usually in most AEG sets)

Using a 9 tooth bevel on a 13:1 will make it a 15:1 set or 10% increase to 13.5:1 ratio

Most ratio's are never what they say they are

18:1 are usually 18.65:1

16:1 are often 17.25:1 - what a con eh ???

(some are 16.5:1 but most are 17.25:1 and use same 18:1 sectors - just spur alters)

13:1 are about 13.65:1

12:1 are about 12.75:1

(aprox)

you can count up all the friggin' teeth if you like

or mark bevel with pencil (John Wick)

then see how many times the bevel rotates to turn the sector one complete revolution

then Multiply by 3 to arrive at gear ratio

Your 13:1 set will have the bevel turning 4.5 times to one sector revolution

but yeah your ratio would not have changed using Krytac bevel as it is 10 tooth

(or should be)

Just you have 4 latches/lugs compared to say 6 on SHS

it might not quite catch asap and might have a slight chance of possible roll back

(on rare occasions but at least should work/mesh with Krytac pinion blah blah blah)

Ah - sod this, you will suss it out I'm sure

 

[richmt11]

Hello My dudes!

So thanks for the help so far it has been much appreciated.

I have attached a screenshot of my current results in the control station.

I not have the 13:1 gearset installed, with the RA high torque motor from AK2M4. I also switched back to my original nozzle, as i couldnt be bothered shaving that one down for now, ill wait until another time. Also i have to shave down my trigger so i can work on sensitivity 1, if i want to. Although 2 feels fine. Also as an aside note, i had to use the original bevel gear. There is no way i can get the SHS gear in the box, its just too tight.

So i am about ready to put it in the gun. but just wanted to check my figures. Now in my (noobish) opinion the gears are shimmed beautifully. Right now the motor isnt getting hot through the grip after say 500 rounds of full auto/burst/semi mixed. Given i dont really play full auto thats not a big deal, and i probably only shoot up to 500 rounds per 30 minute game if i am really spamming! Normally im only doing 2 mid caps, which is half that. Also i cannot hear any gear whine sound. Just the clack of the piston returning. I actually followed the "Shut Up Gears" video to a T, including the DTI, as i have one for setting up loadcells!

So whats with the high current? As i said nothing is getting hot like before, just warm.

The last thing to do is put my 11.1V LIPO in when it arrives, i should get a 33% ROF increase? Bringing me to around 26RPS?

Cheers

Rich

View attachment 33101

 

[Davegolf]

Good job, it is satisfying when all is done for sure!

RE current draw, those motors wont get hot, and heat isnt entirely relative to current draw, you have fitted a stronger motor, it will naturally consume more current to function, especially on start up, thats the nature of a DC motor and why average current draw on Auto is far less then Semi.

What spring are you pulling, an M100?

RE ROF, what have you done with regards to PME? 26 RPS is getting close to causing a problem if supporting mods are not in place, which will eat your piston!

 

[Sitting Duck]

Current is a bit high on a SHS/RA on std 18:1 gear set

About 17-18amp is what I get on a 13:1 set and SHS but could be reading differently

BUT - big butt Kim Kardashian in fact

Mods delete if this is too inappropriate as we have young kids on here

plus can't afford to trigger others but I tried to get her best side

(OK easy on the but/butt jokes back on topic a sec....)

That is If the actual amp readout is exact same as my Power meter....

ALSO - another BUT/BUTT but not quite so big (Niki Manaj)

(nope I'm trying to stay on topic here than lower the tone with cheap funny pics)

Also Mrs Duck in in same room so I gotta behave a bit

The Titan's AB might be playing a part and/or it is reading it all

feeding the exact precise data into a mini Nasa computer chip

working out the stock markets & exchange rate uploading data to Skynet PC

Or in other words - I wouldn't sweat it if grip & stuff is running much cooler etc....

Like them ladies figures - it could be a bit inflated or slightly false (pahhhh "slightly")

OK enough of the sexist innuendos - don't wanna trigger some people

Cold shower & back on track......

you got a 30k motor (ish) hitting about 20rps as expected on decent 7.4v 25c

NOW when you jump up to 11.1v you will ramp up the juice 50% on 11.1v

you will boost this by 50% or a little more

Gun is already doing the cycling work so is already running so imho you get a bit more

(if everything was 101% like for you might get say 55% rof increase imho but hey ho my theory)

REMEMBER why Kyrtac put that sticker on there warning about 11.1v on UK spec guns

Coz they also may have used batches of 30k Krytac motors and UK guns on 11.1v mashed up

In reality about 25rps on non-AB Mosfets the gun will overspin lots and risk double fire on semi

The damn gun is talking to you saying easy on da juice.....

Now you got AB in your flash bastid Titan

AND you SS on a m120 too so you should be OK to approach 30rps

Try a max 25c 11.1v and consider option to pause/slow the cycle a smidge if need to

Personally hitting just under 30rps like say 27/28 in the gun you "should" be fine

and perhaps about the best limit without risking stuff too much long term

(you could be OK up to 35 say but I wouldn't push it with 35/40c crazy stuff or 13:1)

You might lose a smidge response on std gears over 13:1 and final speed

but really - way more zest than before with option to push it near 30rps now you SS

The amps - well think the cpu is working everything else in the world like I said

distracted by a large derriere or something on top of a bit of extra AB or something

Proof of pudding is in the eating, if it runs well, stays cool, sounds nice

Then you are doing ok in my book

I use amps as guide only and perhaps to find that perfect sweet spot on height

But how it sounds & feels also....

IMHO ifyou have to tweak the height more than half a turn up/down

then your shim/height was wrong to begin with

Rogers being the perfectionist would say if you altered the height by 1 degree it was wrong

But it is a good idea to study his methods and kind of wind it back a little in reality

Everybody has their own methods, I kinda follow his stuff without the drilling

I got a depth guage on a mobile stand/bracket to clamp on box

I get a max push on bevel to pinion rotate gear a few times

(gear sits at 6 o'clock and then spin gear sits at 5 + 7 o'clock readings vary a whisker)

Get average reading pushing bevel to pinion modestly (not rammed or kissed)

Then take off about 0.15mm to 0.20mm max " WALK " as he calls it

did use a 0.10mm walk but seemed to not quite be quite right

Nothing that precise - usually take off anything from 0.15 to 0.20

or WTF there abouts what ever I get near with the shims ffs

On a small 0.05mm variation it is f**k all considering all other factors

like actual motor angle is good/crap or how well/bad the bevel+pinion actually mesh

(add a smidge of grease to poor pinion though)

Just use the damn thing - stop worrying or overthinking stuff

I'm the odd unique / no odd is the word, weirdo on here if you please

Also - somewhere in this short condensed post is my response after some picture

(If you are excited by a Power Meter then you really need help - the other pic ffs)

 

[richmt11]

Good job, it is satisfying when all is done for sure!

RE current draw, those motors wont get hot, and heat isnt entirely relative to current draw, you have fitted a stronger motor, it will naturally consume more current to function, especially on start up, thats the nature of a DC motor and why average current draw on Auto is far less then Semi.

What spring are you pulling, an M100?

RE ROF, what have you done with regards to PME? 26 RPS is getting close to causing a problem if supporting mods are not in place, which will eat your piston!

Hi Dave,

I am running a short stroked M120 to encounter the PME. I have AB set to automatic at the moment (got to learn on that front what its doing and have a play). But right now its stopping dead on where it needs to.

Thanks for the feedback, think im gonna stick it in the gun and have some fun

Current is a bit high on a SHS/RA on std 18:1 gear set

BUT - big butt Kim Kardashian in fact

....

Thanks again Duck for your help. Yes i think your right that given the active braking and other circuitry its probably playing a part in the current reading being out.

I really does sound and cycle beautifully now im well chuffed.

The 11.1V i have coming is a 20/40C so i think its quite modest compared to what some people are using. Ill definately throttle the ROF in the mosfet if it starts giving problems. I think as i originally said (or maybe thought), my target is around 25RPS. So i know (now) that i could have done it easier (and cheaper!), the journey was a good one to go on at least!

Cheers

Rich

 

[Davegolf]

Ahh i thought there was strange goings on! Thought the OP was running 13:1 and a stupid spring!

WIth all that in mind i would say your current draw is spot on mate, 32A on Semi pulling an M120 is good.

16 TPA and 18:1 20 RPS is pretty much spot on, but as said above 11.1 would kill it, that equates to 32 RPS, you will def ned to throttle that back, start slow and increase to your desired obv not other way around! Dont wanna make more work for yourself!

Also keep an eye on your cut off timing, tappet delay to avoid double feed as pointed out above by Sittingduck too.

I like to make things work mechanically rather than rely on tons of active/passive brake.

Glad you enjoyed it it all, its nice to know youve got a sorted gun

 

[Sitting Duck]

Welcome sir,

Think your new battery will work out just perfectly

When they say 20c/40c it is still a 20c with a max 40c burst

But afaik from what RC mofo's say a 20c/40c is still a 20c not a 30c

That said it should be just about right, on std gears

as it is not working harder on say 13:1 gears etc....

So if limited on battery space - as you now got 3 cells than 2 on 7.4v

You often have to be a little more selective in some stocks/guns/options

So many ways to skin a cat or get to a more responsive gun

Use what ever method works best, take time with care/attention stay sensible(ish)

and you should get a lovely crisp gun that lasts

It is all a learning curve, I'm still screwing up and learning (just not so frequently

(hopefully)

ignore my childish comments, just refusing to grow up I guess

Mrs Duck often says I never listen to her (or something like that she said)

Loads of clever mofo's on here & a few elsewhere all advised me

but I didn't listen and found out the hard/expensive way how stuff works best

(live n learn I guess)

Think you "should" be just about right - even fresh off of charge on 20c 11.1v

As you SS a m120 etc... (I too stick with ye olde mechanical non AB cheapo stuff).

But keep an eye on her to stay just under 30rps or time it down if needed

Awesome stuff - well done & full marks for not just settling for "that will do..."

Or

"f**k me that sounds rough, oh maybe it will settle down once it's run in a bit..."

Yeah my first few builds wasn't anything to be proud of  :blink: :blink: :blink:

PS - your battery in your Titan display is a bit low....

Max - 7.61v ???

Each LiPo cell is 3.7v but can be charged up to a max of 4.2v

So a fresh 7.4v comes off charge at up to 8.4v or 8.36v average balanced

So a fresh 11.1v will be 12.6v freshly charged or say 12.5v-ish

So 18/19 on your battery will hit another 10% on fresh battery say getting you 20rps

11.1v will hit around 30rps or there abouts, maybe a smidge just over freshly charged

Normally you need to watch Lipo's dropping to say near 3v or it may struggle to charge

(or cells can start to take damage from low volts (and overcharging past 4.2v limit)

A iMax B6 can be a bit picky to charge up a low volt LiPo but you can trickle it up & charge

(see youtube for more details about getting a low volt LiPo to charge)

Luckily, your super duper bells whistle Titan should flag up if juice is getting low 3v per cell

11.1v's in " normal " guns can still seem to have some punch at 9v

7.4v's at 6v really crawls or stalls

But it is easy if people are not careful to keep running with a low 11.1v

(still packs some wallop/juice but its getting quite low)

Anyway, you will be fine coz Titan will alert ya if battery starts getting low

Just saw the juice was a smidge low on fresh 8.35v juice,

but think those figures might be just a guide maybe ???

Who knows, it works that is the main thing - peew peew peew

 

[richmt11]

Hello my dudes.

It seems a bit silly to come back to this so far on! But i just dont play that much and i had some other toys to play with!

Anyway, an update to this, i have a concern.

So in addition to all the internal changes, i also swapped out for a ZCI TBB from AK2M4. With a straight swap, so original hop up parts the gun would be all over the place regarding bb's hopping. So it seems the gun doesnt like the ZCI. Ive put them side by side and they dont look off. So anyway im not so conerned with that, i can put that barrel somewhere else at some point.

The big issue i had, is on that day i just put the Krytac away and played with other guns. Changed the barrel at home and put it on my brother in laws chrono. Now seriously this things FPS (on the original barrel) is consistent! Its maximum +/- 1 FPS after 30+ shots. The only issue is its consistently low!

I stripped it thinking i had stripped some teeth to something on the piston. Opened it up and inside it is beautiful, no wear or damage. Looks the same as when i assembled it. Ive only put about 1000 rounds through it messing about and testing.

So my FPS is bang on around 250. But why is it so low?

Is there a chance the M120 i was sent from AK2M4 is labelled up wrong? Or what can it be.

As i said compression is perfect. Ive checked the parts now its out, and given the FPS is so consistent compression isnt an issue. It was an M120 i had, and SS it 3 teeth should have given me 350.

The only other spring i have/ever had laying about is the stock Krytac one. Thats in my MP5 which chronos at 330fps. So i dont believe ive mixed the springs up somehow. Because even if it was stock spring which gave 350 with hop set correctly, taking 3 teeth should put me about 290 and its lower than that...

Im going to rebuild the gearbox as i dont feel the problem lies there but should i be ordering a better spring and testing it, is there a chance mine came and was wrong?

Cheers

Rich

 

[Sitting Duck]

your maths is correct m120 SS 3 teeth about 350fps expected

each tooth remove drops about 16fps I have found

or take 5 or m5 off the original mxxxfor each tooth removed

(some say 12fps others say 20fps per tooth - nah just go with 16 or m5)

so m120 - 3 x m5's leaves you with m105 = 345ish

two things - mislabelled spring - hmmm can happen

a mislabeled spring would have to be about m90/m95 !!!!

taking off m15 through SS 3 teeth = m75/m80

328fps x 0.75 = 246

328fps x 0.80 = 262

so if your spring was badly mislabeled it would likely be a m90/95

or

blowing lips is where you are losing the 100fps

the nozzle not sealing on bucking lips with zci barrel or how it got reassembled

see if you can push the barrel into hop a bit more maybe ???

is there a spring on hop ensuring the hop is set fully back against the front of box

often a mag clips in and "can" try to pull the hop forward away from box - losing airtight seal

the m120 spring should have been a smidge more awkward to fit in Krytac but it is Quick Change

so maybe not notice it so much like a reg non QC box

Springs can get mislabelled, one way to know for sure is test spring with another known valid spring

say in a APS UAR & chrono as UAR has one of if not the fastest spring change I know in situ

http://www.airsoftspecops.com/Forums/DisplayComments.php?file=Electric Tech/APS_UAR_is_an_Excellent_Spring_Testing_Tool

if you was local I could test it for you today but sounds like you are miles away from Surrey/Kent

so check the hop or ratherbarrel/bucking is pushed back in hop fully

Krytac nozzles are a smidge shorter that SHS nozzles, but if change to a longer nozzle you may get feed issues

So do some checks or replace original barrel and reassemble carefully & retest

think it is likely a seal issue just as much as a low spring possibility - but without more tests

it will be very hard say which it is

It could be a bit of both say a m105 spring powering to say m90 @ 300fps aprox

then a seal blowing at bucking lips dropping down to 250fps

f*ck me that would be nightmare to establish for sure

I mean if somebody has a guarder sp110 = m120 and that fires at 250ish then deffo it is a seal issue

but if it is a seal issue - then a quick fiddle/refit & test should reclaim most of missing fps

(well I would have thought so)

 

[richmt11]

Cheers @Sitting Duck I’ve had both the barrels in and out so many times. But I put the ZCI in, really forced it back as far as it’ll go took extra time to ensure its home and put it together and it’s “fine”?

the question mark as it’s one extreme to the other! I’m chronoing 393!

how much fps will the spring loose when it beds in? As I’ve heard that’s a thing.

also I’ve not set the hop, haven’t got the range until this weekend. But in the past setting the hop has only dropped 10-15fps or so?

cheers

rich

View attachment 34782

 

[Sitting Duck]

Is there a chance the M120 i was sent from AK2M4 is labelled up wrong? Or what can it be.

the question mark as it’s one extreme to the other! I’m chronoing 393!

Uhmmm you didn't by chance purchase a Guarder Sp120 ???

https://www.ak2m4.co.uk/internal-parts/springs/guarder-sp120

SP120's translate to M130 or just over

Also Pete has quoted a list of spring powers he says taken tfrom their site

where SP120 = 393 fps which that figure is total bollox

M120 yes maybe but Guarder spring SP rating are at least m10 or even m15 more....

Soooo you probably need a "proper" m120 393.6 which the SS drops to 350-ish

OR get your hacksaw out and chop the spring a coil or two

ALSO - as if that crap wasn't enough already Guarder is an irregular spring....

WTF does this matter ????

Well you are supposed to fit the tighter coil end at the back on spring guide....

IF you fit the tighter coils inside the piston you will increase the fps by about 10fps

(just by fitting a spring - irrgeular spring one way or the other can make a difference too)

I'm not a great fan of chopping springs myself as it is a bit more of guess work even that SS

but as Krytac is quick change box of a sort it is not so bad messing about a bit

I'm guessing you bought a SP120 - or something along those lines

even a sp110 might still be a smidge hot if you got awesome seals in Krytac

a sp100 might end up giving the right 340-ish figure perhaps ???

But I don't use Guarder's myself - I just know the starting/stock fps

then Short Stroke that spring based upon knowing its starting fps

Or locate/test a spring that is a smidge higher/lower in my APS UAR

Most cheapo springs fade - alas Guarder's & maybe Lonex springs do not fade hardly over time

So either lower Guarder or choppy choppy

maybe a Sp100 & ge ready to chop the present spring as a fall back

reckon as a starting point you need to chop most - say 66% of the tighter coils off back

then clamp the remains together to level off the end neatly & finished correctly - but still a guess tbh

also note you can flip a n irregular spring to +/- 10fps perhaps

WTF are Guarder springs mislabeled ????

Well they are not as such some will argue

SP stands for SPRING POWER not Meter (328fps) rating

Also this SPRING POWER is performed on 0.25's not 0.20's

hence reason why power rating is 40fps or so over expected M120 power

should explain why you are 45fps over the expected result

Ahh what fun these poxy toy guns eh ????