[AGM M4 GBB]

speculation on my part as I haven't fitted that setup to confirm one way or the other, but:

 

1 I'd expect issues with level of the top rail versus the upper on the rifle (which is going to be all the more noticable on that style of front set where one is meant to be a seamless extension of the other)

 

2 using the barrel nut supplied with that front end you'ld most likely need to move over to a thin shouldered barrel, and away from the thick shouldered WA style barrel that AGM use on the 061/062 models

 

if you opt to go the other way i.e. a standard KA RIS where normal AR delta ring is used, then you'ld likely just have to grind off the two knobbly bits on front face of the AGM delta ring, and dump the original AGM 061 undersized plastic end cap in favour of a conventional pressed metal one as I *think* that's all the mods required to get that sort to fit

 

 

 

 

[AGM M4 GBB]

3rd option for a buffer tube would be to get someone to thread you one from mild steel tube, pretty sure the thread dimensions are somewhere in the thread (probably around sometime in July) only other issue is that you'ld need toget them to fabricate a new multiposition stock block for under the tube too as you need it in carbine config (chap who posted the thread dimensions was fabbing a tube for a fixed stock rifle)

 

if you go with a new lower you'ld really need to buy it along with an upper as theres very few 'cross manufacturer' pairings of upper and lower that work on the WA platform most manufac do their own thing with the dimensions of the receiver tabs

[AGM M4 GBB]

Thanks snorkel, to adjust the hopup you need to split open the receiver? Can't easily see where you can adjust anything through the ejection port. Also I just noticed on the ACM that part of the loading nozzle has snapped off, a 2cm prong!! The port cover is also missing it's spring so it won't close and the fore sight has a crack in it. All fixable I'm sure.

 

 

pull back the delta ring and take off the lower ris panel and you can access the hop adjuster drum theres a slot cut in the base of the outer barrel that lets you access it

 

to swab the hop rubber knock the rear take down pin out of the way withdraw the bolt carrier and have at it with a cotton bud thru the ejection port

 

do you mean the long square profile plastic part under the loading nozzle assembly - if so thats the bb pickup that strips BB from the mag by sounds of it you need a new loading nozzle assembly

 

PM me regarding any bits n bob I should have spare front sight and loading nozzle knocking around if you're stuck probably an ejection port cover spring too

[AGM M4 GBB]

most likely cause for your low FPS is the positive pressure system being used in the ACM nozzle (either on its own or in combo with a greasy hop rubber)

 

positive pressure - the flute valve inside the nozzle is held forwards in the closed position with a spring that sits behind it - the pressure of a BB sat in front of it is what should then hold it open to route gas for firing

 

you chamber a BB - if it sits slightly too far forwards then theres nothing to act against the flute valves spring and push the flute valve open

 

if you have a greasy hop rubber theres no grip on the BB as its being fed into the chamber , likewise if you dial the hop back to zero - both of those can see the BB allowed to seat too far forwards on loading

 

I'd use a cotton bud to gently swab the hop from the breech side to try and remove any grease then apply a little hop and see how it goes. Chances are it could still be pretty craptastic as PPS isnt all that great, in which case convert the nozzle assembly over to negative pressure system

 

in the negative setup the flute valve gets pushed back into the open position by its spring, so it doesnt extend from the nozzle and doesnt rely on BB pushing against it to hold it open for successful firing cycle

 

I'll have a look see if the ACM nozzle parts can be rejiggled into negative config failing that a thrd party nozzle assembly like the AGM one that comes in negative setup would do the trick

 

 

[AGM M4 GBB]

the uppers are close but not directly interchangeable you'ld need to mod an AGM upper a little

 

by looks of a test fit the problems are with alignment of the rear pin - it doesnt get down deep enough to pass thru the ACM receiver

 

you could

 

open up the hole in the rear tab of the AGM upper or

you could take material off the lower edges of the rear of the AGM upper to let it sit a little lower

 

second option would probably be best it'll ensure that the bolt carrier gets a straight path into the buffer tube

 

I wouldnt reccommend doing it the opposite way around (AGM lower and ACM upper) when you put the rear pin thru that combo the upper will be stood off in relation to the lower with a visible gap between the two

 

increase the top of the hole on the ACM upper rear tab and yes you'll get it to physically fit down snug against an AGM lower but there'll be nothing to hold it down in that position, and as a result you'ld get a lot of play between upper and lower.

 

GHK mags- the ACM lower will need material taken off of the inside of the magwell, Id advise leaving that till you decide wether or not you're happy with the guns performance running the stock magazine and 5ku mags (which the stock mag is identical too) carry out the mods on the lower to take GHK mags and the stock mag and 5kus will no longer be as tight a fit in the lower as they otherwise could be if you left it alone.

 

[AGM M4 GBB]

@ mutikasha, aye you can thumb the safety back to semi to disengage the hammer lock

 

but you leave yourself with the issue that the hammer lock is a bit of a hair trigger on a lot of these rifles, if it fails to do its job it won't need to be tripped by the bolt carrier, and if the unmodified selector is on auto then that 500 FPS DMR will fire auto

 

 

@weekenny, personally Id leave it decocked with selector on semi, less stress on the hammer spring

 

the reason its like that is it follows the fire controls of the real AR

 

 

[AGM M4 GBB]

Once again I was amazed by WA platform. You can easily go from full auto 400 fps to 500 fps semi auto only in just one easy swap of the bolt carrier...no messing with firing group. I just dremeled the part of the BCG that strikes the hammer lock and thus disabling the full auto feature. A+ for that.

 

 

 

turning the bolt carrier into a semi-auto carrier doesnt turn the rifle into a semi auto one, it turns it into a full-auto selectable rifle that will lock its hammer up after first shot on auto and needs switched back to semi to clear

 

you're better off modding the selector to remove the bump that disengages the semi auto sear (that will ensure that the selector is always set to semi no mater which of the two settings you turn it to)

 

 

 

 

 

,

 

 

[AGM M4 GBB]

Ok my ACM arrived today

 

2) It feels way heavier (without mag) than a D-Boy metal AEG M4?? Thought they were meant to be lighter?

 

4) After I ran out of gas the mag would no longer accept gas it just passed right through, then I noticed the valve stem wasn't fully out, pressed the sticky up triangle bit on the mag and it popped out and all is fine again, is this normal?

 

5) It appears to have a metal hop chamber or what I think is the hop chamber. Looking into the ejection port with the bolt back, the part just inside the castellated bit looks to be some sort of alloy (perhaps someone can confirm this is the case on the ACM)

 

6) Front and stock are solid (small wiggle when fully extended) the only movement is between the upper and lower, now is it wise to gently squeeze the lower at the front pin area in a vice to sort this, or am I likely just to crack the lower? Is there a tried and tested fix?

 

2 yep the receiver is a lot chunkier construction than that on a typical AEG M4

 

4 To be expected. When you fire the gun and the mag valve gets depressed the triangle bit is a valve lock - that pops up and locks the valve open. The valve then stays open till the bolt carrier runs over the top of it during blowbacck and forces it back down - the valve can then spring back to its fully extended (closed) position. When you run the mag out of gas then the bolt cant recoil after the last shot, doesnt run over the valve lock which leaves the valve lock engaged when you remove the mag.

 

5 yes hop chamber is pot metal - is a slightly weird design with a hop rubber all of its own. Can be swapped out for a CNC'd alloy one and a normal WA style hop rubber if you prefer just dont lose the other parts of the original hop (adjuster actuating arm and pivot pin) you'll need those to complete the third party hop unit.

 

6 personally Id just live with it rather than trying to pinch it tight If theres a lot of play you could fit a G&P or RAT adjustable eccentric pin to pull the upper down onto the lower (though you'ld likely need to open up ID of the holes in the lower and upper to get those to fit).

 

[AGM M4 GBB]

not sure the G&P bolt carrier is one worth buying, its nice enough for a stock part supplied with a rifle but its still ultimately just a diecast bolt carrier and folks still have a tendency to swap it out.

 

I'd be more inclned to stick the cash to one side and see how much mileage you get out of the standard carrier supplied with the rifle, though that does leave you with prospect of a bit of a delay waiting for a new bolt carrier to arrive as a seperate order if you run with the ACM one untill it breaks.

 

[AGM M4 GBB]

trivial between the bolt catches on the AGM and JG

 

bottom line all three guns are full of cheap *suitcase* that shouldnt be relied on. You might hit lucky you might not, best to budget for not hitting lucky.

 

Of the three Id buy the ACM cos the parts worth keeping on it are greater in number than parts worth keeping on the other two

 

receiver is metal with decent fit (JG is plastic), can take off the shelf buffer tubes if you fancy a different buttstock (AGM is non standard), better defined threads on upper receiver (AGM arent cut as nicely), less wobble on the RIS, takes any off the shelf bolt carrier (JG is fussy) has a steel bolt catch as standard (10 bucks you'ld need to spend on either of the others)

 

Mag its supplied with is a wee bit better than the stock AGM one, while the recoil spring it uses is halfway between the strength of an AGM one and RATs summer one - which makes it just strong enough for half decent ROF using heavy bolt carriers without being soooo strong to make the gun a short stroking gas hog.

 

trigger hammer and selector are usual potmetalonium as found on JG and AGM too Id budget 30 bucks for swapping those out for steel ones on any of the three you buy Same goes for the bolt carriers you might get a mag or two and see it collapse or you might get umpteen thousand rounds its luck of the draw. Another 80 bucks to one side for that eventuality.

 

 

 

[AGM M4 GBB]

tbh design differences at that level are trival - the ACM uses a one piece steel bolt catch the others use one with an insert

 

 

 

[AGM M4 GBB]

I have the ACM CTR stock on mine, fits fine and no wobble...

 

isnt that an AGM062 though? (he was asking about the ACM)

[AGM M4 GBB]

well, I can confirm that the Element UBR fits on the ACM M4

 

 

excellent

 

[AGM M4 GBB]

that is the idea, shroud all the barrel, with a noveske krinkov style flashider....

 

by the way, thanks for your help.

 

you're welcome

[AGM M4 GBB]

if you're going with a larue free float system then you'ld just use the free float barrel nut supplied with it no need for a conventional barrel nut

 

the one I used I pinched from an element delta ring assembly that would be same as this one (the delta ring is alloy I just pinched the steel barrel nut from it)

 

http://www.gunnerairsoft.com/catalog/produ...roducts_id=1153

 

re the larue handguard length are you sure you want a 9" barrel along with a 9" handguard?

 

fit the two together on one rifle and Im pretty sure the front of the LR will extend far enough to cover even the flashider attached to the barrel (whereas a 9" LR along with a 10" barrel will have the entire barrel shrouded except the flashider)

 

 

eg heres an 11" LR fitted along with a 12" barrel

 

 

CTR stock will it fit the ACM buffer tube? the ACM tube is 1.171" diameter which is civilian spec, the inner diameter of the CTR stock would need to be wide enough for it to fit.

 

If the CTR stock is expecting to go on a milspec tube then it would need the stock tube on the rifle to be 1.145 to 1.150" diameter, and the only way then for you to be able to fit it onto the ACM is if the ACM tube can be replaced with a real steal milspec tube, or a WA GBB tube that adheres to that mil spec dimensions (ie G&P etc) Trouble is until the one I ordered turns up in the post Ive no way of telling wether one of those will screw onto the ACM receiver.

 

[AGM M4 GBB]

nice, did the thread of the AEG fits withouit problem in the the body?

 

yep the element steel AEG barrel nut screwed down nice and solid (though the ACM supplied one is solid in that respect too) - I used it in preference over the standard ACM barrel nut because

 

A it was steel (the ACM barrel nut is alu)

 

B it was cut for thin shouldered outer barrels which the steel multi-part outer barrel kit is one of - the ACM barrel nut is cut for thick shouldered barrels. I could have used the ACM nut by just dropping some spacer rings down onto the barrel before screwing down the ACM nut (the chinese multipart barrel comes with a set of spacers)

 

 

[AGM M4 GBB]

thanks, if u can take a some pix while we are waiting the review!!

 

 

I would but this ones already been totally stripped and rebuilt so isnt really representative of the stock ACM rifle:

 

KG GunKote Flat Moly grey upper lower and carry handle

 

steel chinese multipart barrel set (just using the CQB length section and shortest extension from that)

 

old set of M4 handguards I had knocking around

 

steel Element AEG barrel nut

 

RAT 3 round burst kit

 

G&P steel mag catch

 

element steel buffer lock

 

steel RAT bolt carrier

 

cheap chinese aluminium hop unit

 

red JDT hop rubber

 

aluminium buffer

 

RAT summer spring

 

GHK mag

 

I've another one on its way I'll photograph it for the review with standard parts still in it/on it

 

 

[AGM M4 GBB]

Does anyone know what tipe of buffer tube has the ACM GBB M4???

 

I have one (and another on the way) but no buffer tubes to confirm compatibility with other tubes as yet - one reason my review is delayed.

 

Gunners claims it can 'take real tubes' but while it certainly doesnt take AGM tubes Ive yet to see anyone actually confirm that it does take real/WA/G&P/Ino ones, and doesnt just use a different proprietary thread of its own.

 

Confirm it as in actually sitting their and screwing a diferent tube onto it.

 

What I can confirm is that while the inner barel etc are different from WA/AGM etc they can be used along with a conventional WA style hop unit and hop rubber. You can use its inner barrel its adjustment lever and its adjustment drum.

 

1 the ACM adjuster lever can be fitted into my RAT hop unit (and my cheap CNC hop units) the pivot on the lever is a seperate piece rather than part of the lever but thats the only change to that part and doesnt affect it fitting - just pop the lever and its seperate pin into the hop unit instead of a normal one piece lever.

 

2 The ACM inner barrel is cut differently at breach end (just a circular hole for the hop rubber to press down thru, rather than whole top cut away like conventional WA design inners) but again doesnt afect fitting/operation of a conventional hop rubber

 

3 the ACM adjustment drum is a direct swap for conventional WA/AGM/G&P ones no hassles there.

[JDT Steel Bolt Carrier Group Review]

Also, a paintball tank is filled with liquid CO2, right? And it doesn't have that much pressure as gassified CO2 until it expands outside the magazine, right?

 

wrong

 

co2 will exert 850 PSI of pressure at 20 degrees C - lower the ambient temperature lower the pressure, higher the temp higher the pressure

 

the only way you'll get less pressure from CO2 is by preregulating it and filling the mag with your lower pressure vapour at which point you'll get as many shots as the volume of your storage container allows - regulate it down to 100 PSI and store the vapour at that pressure in an M4 sized mag you'll get say 2 or 3 shots, at 200 a couple more, 400 a couple more again.

 

Pump straight unregulated CO2 into the mag you'll get a whole lot more shots..

 

..at risk of blowing the mag up - GHK mags are certainly better than conventional WA style mags but they arent good enough to provide safe and reliable storage for unregulated CO2. The valve block is die cast, the threads holding the tubes onto the block arent designed for that sort of pressure, nor is the thread for the valve itself, even if it did hold out it would be a constant accident waiting to happen with no inidcation as to when it will finally fail.

 

GHK didnt go tot he expense of sticking a honking thick brass tube with a meaty thread in place of the thin walled fine threaded aluminium tube their green gas AK mags have just for the fun of it (and thats on a mag that takes the CO2 caplet in a oner, and restricts the output to a couple of hundred PSI before it hits the valve block)

 

To be honest its pointless exercise IMO - if I'm at home then I could just as easily tap a line from an external rig onto a mag and run the mag at 100 odd PSI from regulated CO2 with none of the risks. Whereas if I'm on a skirmish field then I'd have no business carrying full pressure CO2 filled mags of that sort around with me anyway. One thing to risk embedding bits of mags into my own body if Im daft enough to fill em to that pressure, another entirely to go wandering about amongst other people who havent consented to be potential shrapnel catchers.

 

[AGM M4 GBB]

erm no need to dent the four side guides, just wedge a screwdriver under the front face of the baseplate and lever it up high enough that the pressed metal detente formed near front of the baseplate clears the front of the main mag shell - the baseplate will then slide straight out along the four guides

 

after that knock the split pin out that holds the outer shell to the mag internals, once its out slide the internals out the top of the mag.

[AGM M4 GBB]

yep Id agree with that, even as a big 3d model of where everything more or less should go its worth it. The only real bummer is having to lay out shipping costs for 3 kilos of dead weight you wouldnt be using though if you pick the right gun you could probably flog most of it off as spares and recoup a chunk of the outlay

[AGM M4 GBB]

based on the VAST amount of aftermarket and reinforced parts available for this platform; is it possible to build a complete rifle from scratch yet? or is a donor rifle needed due to availability of misc parts?

 

yes you can wether its cost effective over buying a donor gun depends on wether some parts are available at any given time and what you're planning to build

 

building a bog standard M4a1? then grabbing a JG and snaffling the trigger guard, pistol grip, stock, handguards, front sight, flash hider, gas tube, ejection port cover, charging handle, auto hammer lock, lower receiver tower end plate, pistol grip mount and firing block from it is much cheaper than buying them individually.

 

however if you're building something more distinctive then you might not have use for almost any of that

 

the potentially awkward bits to source are:

 

firing block - the only sensibly priced one is the JDT/Ino block complete with steel bolt stop and firing pin at 30-odd bucks but seems to be out of stock at moment. Only alternatives are ridiculously priced steel one from Japan (if ever there was one part on entire rifle that didnt have to be steel its the firing block) or sourcing one as part of an Inokatsu parts kit (140 bucks set) or as part of a 'prime lower receiver kit' - a collection of G&P parts that go for 200 odd dollars. Buying either of those ties you into a bundle of other parts that arent neccessarily best value for money.

 

pistol grip mount - sits inside the receiver and not all MBKs come with one. I think the G&P one is available on its own from WGC or redwolf If in doubt buy the MBK first and see if its got one before ordering one up as its a pretty useless part to end up sitting with an unneccessary spare of.

 

choice of hop unit needs a wee bit of care and attention as to which one if you're doing a ground up build. The RA-tech ones and clones of the RA-Tech one dont come with a barrel adjuster or actuating arm, you're expected to rob those parts from your existing hop unit so avoid those Prime and PGC hop units come as complete assemblies so those (or their clones) would be a better option for a ground up build - esp the ones that can take an AEG inner barel and hop rubber as you dont need to go buying a WA GBB specific inner barrel then.

 

everything else can be picked up individually the only real annoyance is having to layout best part of 40 bucks for a G&P steel forward assist as theres no cheapy version available just yet

[AGM M4 GBB]

Would love to know more about this ACM M4 when you get the chance man. Not much info out there on it but ive heard that its internally more reliable than the AGM (metal hop, reinforced bolt stop and nozzle) but a little worse in terms of its external aethetic appeal.

 

I'll pop a review up in next day or two once I've thrown a bundle of parts at it and see how it gets on with them. Id rate the external as better than the AGM, I've swapped the complete hop unit and inner barrel with a standard set, but still to see what parts from the ACM hop unit are individually compatible/easily modded.

 

Bolt stop is steel single part unit (no wee insert)

 

bolt carrier group is pretty cheap n cheerful affair (Id rate the AGM bcg higher and it isnt exactly wonderful) though ability to to get decent ROF from the steel JDT bolt carrier group when fitted on this ACM more than compensates for that

 

buffer tube is commercial spec so slightly fatter tube than WA etc - I need to source a milspec RS or WA/G&P tube to see if the threading is on spec

 

GHK mags dont fit out of the box, but doesnt seem much in it so hopefully minor mods should address that.

[AGM M4 GBB]

does anyone know something abot the "ACM GBB M4" at rsov.com? they looks like the AGM m4, but with less things. also less quality? for what i have read, they got some pros, like metal hop up chamber, and other lil things.

 

just had one finaly turn up in the post picked mine up from Gunners ratherthan RSOV but as far as i know its same gun

 

steel bolt catch

steel flash hider

steel front end cap for handguards

steel castle nut for buffer tube - tube looks to be WA/RS thread (ie not AGM proprietery thread)

wobble free receiver (very tight rear pin)

cycles nicely with my modified JDT carrier (still to try it with an unmodded JDT carrier need to dig one out)

 

havent had chance to strip it apart just yet to test parts compatibility should manage that later this afternoon offhand Ive got a feeling the hop unit adjuster might well be proprietary (barrel cut out looks smaller)

 

 

 

[AGM M4 GBB]

one option for a bolt carrier setup that might be worth considering is an RAT steel carrier at 100 odd bucks combined with a stock AGM nozzle assembly

 

Get fed up breaking 8 dollar AGM nozzle/bolt asemblies and you've got a direct upgrade path to complete RAT NPAS assembly by spending the 150 bucks for a full NPAS kit to fit inside it later

 

The RAT carrier has a few thou of stand off between rear face of the AGM pistonhead and inside face of the blowback chamber which might reduce the likelyhood of cracking the piston face (though depends how much of that wear actually is down to contact in that area)

 

last I looked I think the carrier on its own is something like 120 bucks? If so compares favourably with the 80 dollar JDT complete steel carrier which doesnt look to be progressing much in terms of upping its cyclic rate I've had a try at lengthening the active stroke with negligable increase in performance (quite tempted to order up an Ino just to see what exactly has changed on production version)