Insane ROF M4

[Mos]

^ added that to the book.

 

[ChrisMC]

Hi all

Don't mean to drag up an old thread but i did a search on feeding problems on high RPS builds and this came up.

I've just finished building my first complete gearbox. I was after some really nice trigger response so I've modified the trigger contacts which worked great. it seams to work really nice. i watched lots of guides on shimming etc as, despite doing lots of air seal mods before, i have never changed any gears. It sounds good and VERY snappy on semi - auto.

I also ran 16 awg wire which was a massive pain in the arse to fit inside the gearbox - i had to get the dremel out! i also rewired the mossfet so it runs its own trigger circuit in small wires instead of looping through the trigger.

I've also installed shs 12:1 gear and a SHS high torque motor - the best (as far as my research could tell) high torque motor within my budget.

Im running a 30C 3000Mah 3s lipo (11.1v)  -i know this is big, but i had it from another project and it fills the M16 stock and balances the gun nicely. The rate of fire on full-auto is pretty insane.

Now i plan on using this gun mostly in semi but i would like to switch to full auto for the occasional burst. The problem i have is that the gun doesn't feed on full auto.  my guess is that the magazine spring cant keep up with the ROF. I'm using the metal G&G hi caps.  never had problems with them in the past. 

Can anyone confirm that this is likely to be the problem or am i barking up the wrong tree?  would i be better with midcaps, or maybe another brand of hicap?

As i said i plan on mainly using this gun in semi so its not such a big deal, its more for my own knowledge as i don't like to be beaten by engineering hurdles.  Also, i know i could drop the ROF by using a 2S (7.4V) lipo and this may solve my problem but it would mean changing the connectors on all my SMGS that run the 2S batterries and id rather not do this.

Any help appreciated

 

[ChrisMC]

I did sort of - linked him to Legacy's guide which is very good bit of info

look I like to type but sod typing that much crap everytime somebody asks......

However there a few differences between that guide for USA & us Limey's

We have lower fps so we can't quite use m120 springs in normal aeg's unless we are Shortstroking to lower fps

So when Legacy says use this n that - it will often be a tad hot for some examples

The problem with increased rof is double cycling and PE - on lower spring setups this takes place earlier at lower rps

eg: 25rps = over running - double cycle & 30rps PE on a 340fps UK gun

This won't happen on a US gun with a stock m110 to m120 spring as they are not hot for many of their sites

So though it is a very very very good guide it is not to be taken completely 101% gospel for us over here

HOWEVER - it does go into depth about various stages of increasing rof and work involved especially at higher speeds

often depending how fast you really want to go very little needs to change - so you don't have to replace it all with Lonex etc.....

Service ya gun, AoE, increase seals maybe fit spring guide if trying to lighten piston for quicker return blah blah blah.....

Then if getting into 20's leave the stock 18:1 gears in there and heck you could leave a good stock ferrite motor there as well

run on 11.1v is one way but seriously advise fitting fet if going down that amount of juice.....

The extra juice will boost aprox 50% over a 7.4v lipo from extra cell eg: 13rps to 20rps

or fit a faster powerful motor - it really depends on budget and how far/fast you wanna go

However I could go into loads and loads of MY RECOMMENDATIONS - and they may be different to others a little

But I can honestly say to anybody thinking of going nutz......

IT IS NOT THAT EASY - the tolerances and attention to detail on every single poxy little bastid part inside is critical

I learnt - still learning that it isn't a simple case of duplo/meccano of just dropping a new go faster part and it will just work

All them bits n bobs are manufactured with $hit tolerances that fit into $hit gearbox tolerances and furthermore....

EVERY SINGLE BOX IS DIFFERENT TO EACH OTHER - even 2 G&G builds may be shimmed differently if done properly

Each motor can have its pinion at slightly different heights - won't completely affect the shimming a great massive deal but will affect motor height

shimming itself can only be as good as the time and level of detail taken when shimming and even a good guess of motor height is no match for a dial guage measurement - even a rough measurement is going to be better than many people's guess (except Mr Spock teching a box)

The guide needs to be read though to fully understand the detail required and even on a modest 20+ build the same detail applies

Well if you really want it to last as long as possible - coz one part in particular WILL fail - it WILL

Often - very very often the reliability is down to mainly 2 things:

Shimming - I know this gets said every time but so true as bad shimming increases wear on box/gears and especially motor

&

Just how strong your weakest part is - coz it will fail eventually

Normally - pistons strip/snap, bearings start failing and when they do the play can destroy gears also

So when going to higher 20's eg getting to 30 or more a full metal rack is needed and use bushings

I have tried a few pistons but on 13:1 gears pushing it many pistons start to fail but make sure you did ya homework

as full metal rack + PE or bad bb jam slowing a high speed piston will smash f*ck out of box

but try to get the whole piston as truely light as possible to return asap

no bearing in piston - swiss cheese but it only saves about 1.5gms I found - depends on how heavy the piston is to begin with

Bushings - all or nearly all in box especially under the gears - left side of gearbox an absolute must

tbh bushings - will lose a round or two a second but will greatly prolong/prevent failure in gears in the long run

Oh f*ck it my fingers are killing me - the long story trying to shorten it a bit .....

gun is firing 30rps+ f*ck yeah that's great.....

ooh hold up - should of fitted a delay clip maybe coz it ain't feeding properly

fits delay clip - better but still not perfect.... uhmm ergh new tappet spring or lop coils off....

hmmm a little better but just now n then still splutters....

Another reason could be ya fitted a slightly longer o-ring nozzle

(that just so ever so slightly slghtly impedes the bb feeding into hop)

replace/file nozzle coz you didn't check when building it all.....

yeah getting there but just now n then splutters the odd one out....

Oh crap stock high cap mag is $hit, borrow a m8's mid cap or Lonex mag and works flawlessly

So gets new mags - the tech bill is getting higher n higher......

 

Funny thing is all this attention to detail for higher rof and yet

gun still shoots with mediocre accuracy on stock barrel & bucking

Ok to compensate for not considering anything outside the box.......

 

hmmm I wonder if I put a bigger battery in there - famous last words.......

BANG - OH $HIT !!!!!!

famous last words indeed

the story of me taking the pi$$ again and again

Hence the simplest advice it go easy and get to twenties in plenty

a quick question for you all:

What goes: "peck peck peck - BANG !!!!!!"

NOPE - not a chicken in a minefield you might think

but

ME getting gun chrono'd and starting my first game of the day with one of my super duper rapid duck builds

I've broke LOADS and learnt very little despite all the bollox I type

Missed this post. I guess there are a few answers in there.  Maybe I'll just leave it in semi

 

[Sitting Duck]

I've also installed shs 12:1 gear and a SHS high torque motor - the best (as far as my research could tell) high torque motor within my budget.

Im running a 30C 3000Mah 3s lipo (11.1v)  -i know this is big, but i had it from another project and it fills the M16 stock and balances the gun nicely. The rate of fire on full-auto is pretty insane.

If you have done the above then you "should" be looking at....

24rps on 7.4v

&

37rps plus on 11.1v

That is about the best I have come up with on 13:1 SHS HT bushings & SS a few of teeth m115 etc...

Even then when I used a 11.1v 33c on a 10 sec auto burst it hit 40rps & ripped the rack out (PME)

Suffice to say there is always a limit- especially on UK 350 fps guns

A UK regular gun (full stroke not Short Stroked) will be limited to mid 20's due to lower spring/fps

Around 20~25rps you start getting overspin - GUN IS STARTING TO TALK TO YOU

Serious overspin & beyond is where gun starts to shoot twice on semi - TAKING THE PI$$ NOW

Keep pushing a gun like this and and you will be rebuilding your gearbox and picking out bits of teeth soon

(it is not a question of IF but actually how soon you WILL be reopening your gearbox)

Best bit of advice - use a 25~30c 7.4v to hit mid 20's

Drop the 11.1v is a std gun (with a mosfet perhaps) to boost a sluggish gun

The 25rps limit is a sensible limit in the end without going nutz doing more work/homework

Yes if you use a m120 SS a few teeth you will get into the 30's (low to mid 30's)

again even with a bit of homework like I did you still hit a ceiling of high 30's~40rps

So you have to understand and grasp the fact there are limits especially on UK spec guns

and what Legacy says for USA 40rps guns does not translate 101% for UK guns

This backed up by first Krytacs imported (grey imports) came with a 30k motor on a m100 not m120

They eventually started to use slower 20k motor as 30k & m100 risked PME if 11.1v used on UK guns

(wasn't a dead certain piston would strip but 330fps was sailing closer to PME than US 400 fps guns)

Feeding problems are yet another ball ache....

Correct nozzle length

Max tappet retraction - not delay/duration but distance retracted without bottoming out

Checking for hop/bucking lips tight/fouling

Magazines - some work some not so great

Mid Caps are not always better than High Caps, they can jam (had that before)

People describing faults incorrectly....

My gun is firing two bb's at once - unlikely

more like it is mis-feeding/mis-chambering a bb then next bb loads and two bb's appear out of barrel

eg:

1 - 1 - 1 - 0 - 2 - 1 - 1 - 1 - 0 - 2 - 1 - 1 etc.....

The above is likely tight bucking lips or fouling of lips causing it to mis-feed/chamber

then next bb does load and fire OK so two bb's appear out of barrel and everyone loses their $hit

But it is NOT double feeding but mis-feeding/chambering

On M4's some mags mat shift hop a little and this tiny smidge can effect feeding or fps even

Some info on hop problems - well worth a watch:

Wouldn't start modding hop units tbh unless you really know what you are doing and 200% sure

I DO NOT SUGGEST MODDING HOPS !!!!!

BUT some of the TESTS like the bb push test for tight bucking lips is why I posted this

Well worth a watch if you have mis-feed issues to check hop/bucking

BUT there are many reasons why some guns have feed issues as I tried to list

If the nozzle retracts only 5mm then is doesn't matter if a delay clip holds back the tappet for 1 hour

It will never allow a 5.95mm bb to feed if it retracts only just over 5mm say

This is backed up but rapid 50rps+ DSG's don't use delay clips - coz they can't

They might use a tiny sleeve/pipe over two sector tappet cams to nudge the retraction a whisker

but they can't use a big delay clip due to rapid cycling of gun & ultra short fin/tappet retraction timings

I was the exact same - go faster guns are everything

alas it is not that easy to achieve on UK guns

After a sharp learning curve of wrecking more guns than I "thought" I fixed

I eventually came to understand the limits and problems a lot more over the years

After understanding this and a likely limit of mid 20's for reg build guns

I no longer give a f*ck how quick a gun cycles past say 20rps

(Twenties is plenty tbh)

I now no longer listen to how quick a gun cycles in final rps

but more so how ssmmmoooooootttthhh is cycles

plus how well the gun & the owners operates together

(efficiency/accuracy plus if the owner is dick or not)

Long rant - but main point of reply is to ease up on the juice perhaps

if your gun is cycling as quick as I think it might be it won't be long before stuff fails

I personally would wind it back a bit where less PME risk and likely feeds better

(but mainly for reducing risk of PME)

up to you but trying to help you learn from mine & others mistakes

than make the exact same ones as me & others did at first

 

[ChrisMC]

Thanks for the detailed reply.  You made some good points that I wasn't really aware of.  That s a useful video too.

I have had those 1 1 0 2 1 0 2 issues before when messing around with different buckings.

What I wasn't aware of was the issues caused by the weaker springs we use here in the UK. 

I think tomorrow I'll try it on a 7.4. It will mean changing connectors but I can always make some adapters up.

So long as there is still a decent trigger response I'll be happy. 

I did sort of - linked him to Legacy's guide which is very good bit of info

look I like to type but sod typing that much crap everytime somebody asks......

However there a few differences between that guide for USA & us Limey's

We have lower fps so we can't quite use m120 springs in normal aeg's unless we are Shortstroking to lower fps

So when Legacy says use this n that - it will often be a tad hot for some examples

The problem with increased rof is double cycling and PE - on lower spring setups this takes place earlier at lower rps

eg: 25rps = over running - double cycle & 30rps PE on a 340fps UK gun

This won't happen on a US gun with a stock m110 to m120 spring as they are not hot for many of their sites

So though it is a very very very good guide it is not to be taken completely 101% gospel for us over here

HOWEVER - it does go into depth about various stages of increasing rof and work involved especially at higher speeds

often depending how fast you really want to go very little needs to change - so you don't have to replace it all with Lonex etc.....

Service ya gun, AoE, increase seals maybe fit spring guide if trying to lighten piston for quicker return blah blah blah.....

Then if getting into 20's leave the stock 18:1 gears in there and heck you could leave a good stock ferrite motor there as well

run on 11.1v is one way but seriously advise fitting fet if going down that amount of juice.....

The extra juice will boost aprox 50% over a 7.4v lipo from extra cell eg: 13rps to 20rps

or fit a faster powerful motor - it really depends on budget and how far/fast you wanna go

However I could go into loads and loads of MY RECOMMENDATIONS - and they may be different to others a little

But I can honestly say to anybody thinking of going nutz......

IT IS NOT THAT EASY - the tolerances and attention to detail on every single poxy little bastid part inside is critical

I learnt - still learning that it isn't a simple case of duplo/meccano of just dropping a new go faster part and it will just work

All them bits n bobs are manufactured with $hit tolerances that fit into $hit gearbox tolerances and furthermore....

EVERY SINGLE BOX IS DIFFERENT TO EACH OTHER - even 2 G&G builds may be shimmed differently if done properly

Each motor can have its pinion at slightly different heights - won't completely affect the shimming a great massive deal but will affect motor height

shimming itself can only be as good as the time and level of detail taken when shimming and even a good guess of motor height is no match for a dial guage measurement - even a rough measurement is going to be better than many people's guess (except Mr Spock teching a box)

The guide needs to be read though to fully understand the detail required and even on a modest 20+ build the same detail applies

Well if you really want it to last as long as possible - coz one part in particular WILL fail - it WILL

Often - very very often the reliability is down to mainly 2 things:

Shimming - I know this gets said every time but so true as bad shimming increases wear on box/gears and especially motor

&

Just how strong your weakest part is - coz it will fail eventually

Normally - pistons strip/snap, bearings start failing and when they do the play can destroy gears also

So when going to higher 20's eg getting to 30 or more a full metal rack is needed and use bushings

I have tried a few pistons but on 13:1 gears pushing it many pistons start to fail but make sure you did ya homework

as full metal rack + PE or bad bb jam slowing a high speed piston will smash f*ck out of box

but try to get the whole piston as truely light as possible to return asap

no bearing in piston - swiss cheese but it only saves about 1.5gms I found - depends on how heavy the piston is to begin with

Bushings - all or nearly all in box especially under the gears - left side of gearbox an absolute must

tbh bushings - will lose a round or two a second but will greatly prolong/prevent failure in gears in the long run

Oh f*ck it my fingers are killing me - the long story trying to shorten it a bit .....

gun is firing 30rps+ f*ck yeah that's great.....

ooh hold up - should of fitted a delay clip maybe coz it ain't feeding properly

fits delay clip - better but still not perfect.... uhmm ergh new tappet spring or lop coils off....

hmmm a little better but just now n then still splutters....

Another reason could be ya fitted a slightly longer o-ring nozzle

(that just so ever so slightly slghtly impedes the bb feeding into hop)

replace/file nozzle coz you didn't check when building it all.....

yeah getting there but just now n then splutters the odd one out....

Oh crap stock high cap mag is $hit, borrow a m8's mid cap or Lonex mag and works flawlessly

So gets new mags - the tech bill is getting higher n higher......

 

Funny thing is all this attention to detail for higher rof and yet

gun still shoots with mediocre accuracy on stock barrel & bucking

Ok to compensate for not considering anything outside the box.......

 

hmmm I wonder if I put a bigger battery in there - famous last words.......

BANG - OH $HIT !!!!!!

famous last words indeed

the story of me taking the pi$$ again and again

Hence the simplest advice it go easy and get to twenties in plenty

a quick question for you all:

What goes: "peck peck peck - BANG !!!!!!"

NOPE - not a chicken in a minefield you might think

but

ME getting gun chrono'd and starting my first game of the day with one of my super duper rapid duck builds

I've broke LOADS and learnt very little despite all the bollox I type

Missed this post. I guess there are a few answers in there.  Maybe I'll just leave it in semi

 

[KendoKhan]

I never fired a 5.56 in full auto in 12 years in the armed forces,

Reminded me of a scene from this video: (Watch from 1:01 onwards) ?. The joys of working alongside the ANA ?

 

[Rogerborg]

The problem i have is that the gun doesn't feed on full auto

Have a look on YouTube (for why you want one) and then eBay (for buying one) for "airsoft delayer chip".

 

[ChrisMC]

Thanks again for all the info guys.  so i just swapped out one of my 7.4 connectors and tried it in the M4.  It feeds much better and the trigger response is still pretty much instant  so i think that's what i'm going to use.   thinking about it now, i bet i was pulling some pretty serious current on the 3S battery.

The only problem is i don't think, dispite the 25-50c rating, my 1200mAh 2s batteries will stand up too well to a half day on the field in the M4 as they were getting warm off 30-40 rounds of quick semi fire when testing.  Off to hobby king again i guess! My other hobby is flying stupidly overpowered RC planes so i know a thing or two about ruining LiPos (not always on impact) and once they puff, they never entirely recover.

Sitting duck, thanks for bringing me back down to earth without making me feel to stupid, much appreciated. again from the RC hobby, 2S (7.4V) is a pretty wimpy battery, (my last plane was pulling 80 Amps on a huge 85c 4s before the wings folded in flight) so i think i have some prejudice against them that i need to unlearn for airsoft.

ill try to get some video footage to show the trigger response and post it.  it runs really nice now.

Edit, i've also swapped out the spring for a M120 and locked locked it to semi. hopefully will shoot just under 400 and be my DMR

 

[ChrisMC]

Heres a vid on the 7.4V

https://youtu.be/OCZCXEn1xM4

 

[Random_Lincs]

Maybe completely random in regards to your feeding issues but I have a TM High Cycle and find that among my hi-caps, G&G missfeed a hell of a lot whilst Nuprol ones only once or twice in a whole mag. The TM mag that came with the gun though feeds flawlessly.

 

[ChrisMC]

Running well on 7.4V.  I have found that the gun feed less reliably as the high caps near the end of the windage.  If I wind them to the max then the gun feeds every shot flawlessly.  I guess with the higher cycle speed it just needs that extra tension in the spring to push the bb up into the chamber in time.

 

[Rogerborg]

Seems reasonable.  You might even get that with mid caps as the spring unwinds.  Have you looked into a delayer chip?  This is exactly what they're designed to address, and they're only a couple of £££.

 

[AshOnSnow]

On 14/02/2016 at 21:15, Sacarathe said:

It what, the TM high cycle? They all do 25.

For you:

That’s basically a handheld Airsoft CIWS

 

[ChrisMC]

So a little update.

I went for the delayer chip as it was only a couple of quid,  went to test fire it, no BBs came out. Noooooo.

Dropped the mag, that's funny, boo bb at the top.  Something had jammed in the mag. This happened with this mag a while ago and I had to strip it down to unblock it.

Swapped to another mag.  Fed every shot flawlessly. Wahoo!   I stuck in a 11.1V lipo and it fed flawlessly on that too.  I think I finally have a reliable build yay.    I can tell the difference in trigger response on the 11.1 but I'm not sure if it's enough to warrant the extra wear on the motor.  I'm already running it with braking on so it might be a bit much for it.

Anyway, I've ordered some pts epm mags as none of my m4 hi caps have been reliable.  They are supposed to perform flawlessly.

If polished the crapout of the barrel and Overhauled the hop unit too.  I think some grease had got on the rubber from running the gun while the gearbox was only just assembled.  It's hopping a geoffs 0.32 with plenty of travel to spare.

Just counting the days until my next skirmish now.

I thought I had a good knowledge base when starting this build but if anything, I learned more in the 2 weeks since I first put it together than I did before.  Every tiny detail matters!

Thanks everyone for all the help and comments, following your advice really has made a huge difference to the performance of my gun. 

Have fun and play safe!