V3 FPS reduction

[MattCoops91]

Hi all, 

 

I have a CYMA AK from TG that fires ar around 380fps. I'm after a quick home fix to get it down and I think either taking a coil or two of the spring or short stroking the piston would give me the effect I'm after is this the case? 

 

Also I know I could just buy a new spring but I LOVE taking things to pieces and finding fixes myself so that's the reason for the DIY job. Also means I can shim the gears and other bits and pieces while I'm in there. 

 

Thanks 

[Asomodai]

For quality of life or the rifle I would just get a new spring. They are very cheap. 

 

Otherwise yes, both of those methods will drop the FPS, but how many coils or teeth would be trial and error to get the desired FPS. 

[Steveocee]

Take it apart and cut the spring down.

Take it apart and replace the spring.

 

They're pretty much your options. Can't you replace the spring AND do all the shimming and stuff?

[Sitting Duck]

I wouldn't Short Stroke a FULL AK with a 455mm barrel etc...

(you need a full stroke for volume)

Plus you would need a metal rack on piston than just a single metal tooth

 

You "could" remove the alloy piston spacer, but would need a M3 bolt, NYLON LOCKING etc....

This would drop say 40fps from not compressing the spring 8mm~9mm

(you would need a long socket, think a m3 nut needs 5.5mm socket but don't quote me)

It would need to be a screwdriver bit with a long extension type of thing

but is do-able option removing the alloy spacer to drop fps

though lightens the piston quite a bit on light stock pistons

(best used on heavier metal rack pistons if you like fucking about on a tight arse budget)

 

But tbh a m100 spring max if it is a full cm028 455mm barrel - no more

check compression - probably not great, new o-ring, maybe a bit of ptfe on cyl head

regrease from blue cyma gunk & shove it back together

 

Shimming shouldn't be too bad, so unless sounding like a tin of wasps

I'd perhaps look to leave alone unless it is really crap

 

What I would say is that over the years the 028 box used to be black

but in cheapo AK's they were unpainted - and sharp as fuck

That is no real biggie, but the motor frame/cage has a lot of play in it maybe

 

Going by a 028a I had in bits a while ago, the motor cage was a bit looser

and even when tightening it up it had a bit of play in it

Which V3's & AK's have that bit of wiggle room to just tweak motor angle a smidge

but you could just shift the cage a whisker counter clockwise and the angle would improve

(not a massive amount, but just sounded better as bevel/pinion meshed more inline or true)

 

So when you reassemble, testing the box with motor, you might hear it sound

very slightly sweeter or rougher if you wiggle/shifty the motor cage side to side

we're talking a degree or two tops bit of play, but it can mesh smoother/rough with bevel

 

The issue is with cheapo Cyma cost cutting is due to play this minor tweak of cage position won't hold

(no matter how tight you tighten the bolts, plus grip will try to pull the cage too)

So IF you find is sounds better with a slight twist of cage - one way or other

but won't hold that position if cage is loose fit on box

then take a very thin bit of card or folded piece of thick paper

a very small piece of paper on one side only to take up the slack

NOT A BOOK just the bare min, to take up any "possible" slack & tweak the angle a whisker

 

I found 1 piece or a folded (2 bit max) from a Screwfix/Toolstation order slip, popped in one side

was just enough to stop a very sloppy motor cage fitting on a recent 028a

 

The shimming wasn't that bad, it was the loose cage on a cheapo unpainted sharp as fuck v3 box

I mean the 2 halves of the box could have had a whisker of more material imho

the holes at bottom of box might be say 11.75mm thick

& motor cage was say 12.6mm so there was a bit of play side to side too, even after tightening

(but if you put a "gasket" between two halves that would through out shimming)

 

Long waffle, if you find a bit of wiggle, use a piece (not a book) of paper

to find the sweet spot where it might be a whisker less shrilly and help hold position

(you "might" need to very very slightly adjust motor height but only 1/4 turn max)

 

I'm being tarty here, but just saying I found a recent 028 box & frame very loose

even after finding the sweet spot the position would not hold

so slightly bodged it with a tiny piece of thick paper/thin card

(not a book ffs, just enough to take up slack)

 

Your box/cage might be perfectly fine btw so ignore this crap

but reckon Cyma/Spartac have just banged these cheapo guns out

with a bit of less attention to detail on tolerances & slightly loose cage fitting

So as v3's cages give you the tiny wiggle room for angle

on cheapo 028's - it don't hold that position without a little bodge to help it

 

BUT DON'T PUT A BOOK IN IT - just enough to take up any slack to tighten & hold position

(you get a bit of wiggle room, but normally it will hold, not on that 028 box/cage I had recently)

 

IGNORE all of this if you are unsure what I mean & your box/cage fits all snuggly etc....

 

Easiest thing - just but a m100 spring, than remove spacer/cut coils etc....

(just a few ideas to bodge on a budget - that's all)

 

where ever possible - if it ain't broke, don't try to fix it

just a slight tweak & re-grease when lowering the power is rule of thumb

[MattCoops91]

Thanks for all the replies guys. 

 

@Steveocee your probably right, I like to fix parts rather than replace though that's all but on reflection I'll probably order a m100 spring. My only problem is I KNOW the spring in it now is shooting 380fps and I KNOW if I remove some coils it will be less. I don't know what spring is in though so if I replace it with m100 and it fires at say, 355 I'll have to replace it again which isn't a problem but it means yet again I won't be able to play with it on a game day and as I have big gaps (3-6 months) between games that's a bit of a pain (had the gun 3 years and only used it once when they let me keep it on semi and play DMR).

 

@Sitting Duck I agree if it ain't broke don't fix it and I'll absolutely look out for those points when I dissemble. It's not broke at all and actually works really well, just 30 too many FPS. 

 

[Steveocee]

@MattCoops91 the stupidly easy answer would be order an m90 then surely? Yeah if you're wrong at least you'd have a smooth (ISH) firing 300?

[Sitting Duck]

Well I was only guessing it was a full size AK47 with 455mm

(you could have said it was short 233mm variant than a 028/522 model)

 

speak to Pete say at AK2M4, @ak2m4 etc...

 

get him to send you out a gen M100, (hopefully tested or good authority = 328fps)

Springs at "supposed" to be rated on say a 363~400 M4 barrel

(you get a bit of creep up on longer guns & a drop on shorter barrel ones)

*** NB on a level playing field like for like, but tbb, great seals in one gun will vary results ***

 

Most stock guns, especially budget guns are not 100% airtight

and Cyma's are not outstanding piston o-ring & airtight cylinder head

plus nozzle is not o-ring and a bit loose so I'd reckon you would lose most of that extra power from spacer with 3 non-airtight seals

 

So those slight leaks will best part balance out the spacer in situ

a m100 will likely shoot at 350fps in a 455mm Cyma due to possible creep

There is no other extra compression on spring - the spring guide is plastic & a metal washer

(so no extra tension like a bearing spring guide would notch up the fps a smidge from say 4mm compression)

 

There are springs and there are springs even at M100....

Guarder use a SP100 which is supposed based on using 0.25's which means a SP100 will shoot 360fps say

Then there are variations as well as different manufacturers & processing plus the odd mis-labelled ones too

*** NB I'm well out of the loop on stuff btw, but I used to use Element m105 on 300~363 barrel guns & stuff

Element springs do tend to fade a bit more once they have broken in a bit - all springs do but Element a bit more ***

 

a m90 at say 295fps might be a bit too low, a m95 (312fps) might be the lowest I'd go if I was re-doing seals 101%

but it is hard to say get XYZ by dooberry systems and know for certain it will chrono at exact 348.9 fps on YOUR GUN

 

So it is a bit of calculated guess work as is atm based on min messing about, just open to swap spring etc....

 

I'd personally drop in a Cyma steel rack piston and remove spacer etc.. trying stock spring as is

or

use a legit m100 spring in stock one but maybe not go too nuts on improving seals

 

if it was still a smidge too high say 5~10 fps then you could look at:

leaving it parked, pre cocked over night/weekend to fade the spring a bit

if still not quite right then slightly correct AoE which shortens stroke a bit dropping fps about 10fps

 

If you purchase a regular spring - same coiling at both ends, maybe tighter coils in middle

then nowt you can do or it won't matter which way you fit it - it goes in anyway around

 

If you buy a spring that is irregular, it will have tighter coils at one end....

 

now with that type of spring there are tighter coils at back which go on spring guide at back of box

that is the way they are "supposed" to be fitted

But if gun is shooting a bit lower than expected & all else is OK

then flipping spring so tighter coils up front at piston head will give you about 10fps more

 

Yes if you had a 510mm L85 or something with larger volume cylinder and barrel creep

a m100 will almost certainly put you over 350fps

 

But a mehhh seal AK even with spacer I reckon you should be quite close or only a whisker over 350fps

(than once bedded in or faded over a weekend should settle at 345fps)

 

BUT the variation or lottery from buying another spring throws stuff into the mix

(one spring in a titchy gun might give you 300 in a MP5k or 370 in a L85)

So the spring factor is a bit of calculated bit of guess work

based on piston spacer, spring guide and seals n shit

 

if it is a smidge high you can correct AoE etc....

if it is a bit lower you can fix seals, flip spring (irregular), fit a bearing spring guide or add a small piston spacer like you have

 

Should you fix all the seals atm ???

Hmmm maybe not until you establish the average fps first

Maybe change piston o-ring if it is absolutely fucking shit

(it won't be brilliant me thinks)

leave the cylinder head as is or nearly falling out

(and don't bother changing nozzle - you could buy wrong type and fuck up feeding)

 

HOPEFULLY with a gen m100 @ 328 in your AK you "should" be quite near 350fps

a smidge either way then you can address that as & when

 

set your hop really well, fine tuning it as best as you can

maybe use good 0.25's for accuracy firing at 310fps but chrono with hop set @ 0.25

**** BUT chrono'd using 0.20's **** for best results maybe ???

(yeah if gun was just over 350 at say 355fps and I couldn't be arsed to rip it open again

I'd be inclined to park it precocked for a day or two and use 0.25's @ 310 on chrono anyway)

 

Cheapo guns are mass produced for Asia/US markets @ up to say 400 fps

(be thankful you are not in Germany with a 250fps full auto limit)

Alas UK has a 350 average limit, but retauilers should check stuff

 

However you should have obtained the 330fps version or got it downgraded/check prior to shipping

and saved yourself this hassle from day one perhaps

 

others don't mind a bit of messing about and think little of ripping open a new gun

BUT be warned about going nutz, coz even I know a little bit about cheapo guns

it has come at a price of grief & turmoil and first few boxes not working very well after opening

 

so be warned - don't fuck with stuff too much if possible until you gain more experience on stuff

(wish I had heeded that advice I was given)

 

 

by all means have a go but don't go too nuts or overthink shit too much like me

 

best of luck