AGM M4 GBB

[Deepeyes]

I have one of these on the way.

 

http://www.px-airsoft.com/showroom/model/T...815585953003548.

 

I don't think there has been any write up on it so far. I will be doing one unless someone gets theirs first.

[snorkelman]

I have one of these on the way.

 

http://www.px-airsoft.com/showroom/model/T...815585953003548.

 

I don't think there has been any write up on it so far. I will be doing one unless someone gets theirs first.

 

 

keep us posted I was planning to order one just for a look see but I'll hold off see how you get on with it

[snorkelman]

well 30 mins of working the boltcarrier in and out of the upper while smeared with this

 

 

and ended up with bolt carrier looking like this:

 

 

contact point on lower edge just above the valve lock camming suface

 

 

contact point on upper edge just below the gas key mount

 

 

loads of light contact on left hand side

 

again heavier contact on left hand top edge all the way allong from gas key to front of the carrier note little extra contact on the anodized nozzle assembly too at this side)

 

contact on base of the rear of the carrier pretty much all on left hand side

 

 

I could have set about it with some wet n dry but I figured using the lapping compound Id just be lifting material where it had to be lifted

 

End result? Has pretty much cured all the binding that I could feel when I was racking the charging handle and letting the carrier return slowly Prior to this it was tight enough in places that even without a mag in I could actually ease the carrier two thirds of the way home, let go of the charging handle and have the carrier stay there in that position untill I gave it a little nudge with forward assist

 

Now I can feel the carrier return at an even rate when eased back, it slides out the upper when you tip the upper back, and it slides all the way into the upper with flick of a single finger on back of it. I've still to give the surfaces a proper polish up with something finer than 28 micron but is feeling good thus far

 

its similar contact pattern to the one on my RAT carrier that I let wear naturally, just more pronounced cos the carrier is that little teeny bit greater diameter. difference with the RAt is that its light enough and narow enough for the contact not to cause any real binding, instead the RAT carrier can float slightly inside the upper, left and right up and down, it still picks up thenicks and dings eventually but isnt busting a gut trying to recoil.

 

Id suspect other folks would end up with a wider amount of contact wear showing up on their ones if they do the same. This one has been stripped, stuck in a caustic soda bath (long to etch away enough material for the fire control markings to disappear) and then refinished with gunkote - so internally its got a very light coat of gunkote versus the big fat coat of stuff AGM slaps on them at manufacture.

 

 

Once I had the carrier all apart again to clean out any bits of paste that had worked their way into it, I gave the inside of the gas chamber a good clean out too. The manky oil it ships with had left a filthy gunged up mess inside it - to the point where the nozzle tube just plain refused to retract under spring tension when the oring was fitted (even when dry).

 

I cleaned it and then gave it a light run over with 1200 grit wet n dry inside using a 16mm diameter rod to wrap the wet n dry round. Was just a really light polish with that.

 

After that was done, when the oring is back on the piston and left dry the whole thing can whizz back in under spring tension. A little bit of oil into it and it slows down just enough to show its getting a decent seal (but still retracts at an acceptable rate).

 

 

Chuck that back into the rifle with an AGM mag worth of Abbey ultra, a summer recoil spring and an aluminium buffer and the ROF has pretty much doubled. Dont have a chrono with a ROF counter on it but its way closer to the 11 RPS an RAT carrier gets, so Id guestimate at 9 or 10 RPS. Certainly acceptable ROF versus the tractor-like dugga dugga dugga it was churning out before

 

Trouble is the only mag Ive got sat here at the flat Im working in at the mo is one solitary AGM one, and the rifle doesnt get on well with that at all.

 

Push the AGM mag up into the magwell it adds a bit of resistance to the nozzle asembly and as a result the gun always cycles just a hair off of its full stroke (doesnt go the last few mm to trip the bolt stop on empty)

 

Let the AGM mag sit where the mag catch locates it so theres no pressure being applied ot the nozzle tube and yeh the bolt carrier will blow back fully and trip the bolt stop hurrah!!, butt ohoh not so fast- the damn valve lock on the AGM mag I have here then doesnt get tripped back out of its locked position then, so the mag vents all its gas grrr!!!

 

cos of that I'm going to sit and strip the AGM mag down and get rid of the valve lock see if I can get the gun cycling fully with bolt stop engaged (I dont see the carrier being at fault on this - the real issue here is a worn valve lock on the mag and too much tension then being created against the nozzle by pushing up the mag to get the valve lock high enough)

Edited September 28, 2009 by snorkelman

[Luis21]

Fortunately, I didn't have to do everything that Snorkel did to get his BCG to cycle.

 

All I had to do was file down the O-Ring a bit so that the loading nozzle could return under its own spring tension.

 

My 5KU mags cycle the BCG well, however my AGM does not cycle the BCG at all. All it does is blowback the bolt carrier about 25mm and the loading nozzle stays stuck all the way forward.

 

When I push up on my AGM mag though, the BCG cycles..... I'm starting to think that the mag catch might be worn. I'll make the AGM mag seat higher so it can work.

 

Also, I filmed both the 5KU performance report and the JDT BCG review. However the JDT carrier review is 13 min so I cannot upload it on youtube. I'll have to refilm it down to less than 10 min.

 

Both vids should be up today. Around midday.

 

Thanks,

 

-Luis

[mutikasha]

@snorkel

 

How does your forward assist work with all the BCG you put in your AGM so far? My doesn't interact with the stock carrier or with the replacement ones.

 

Another thought... that o-ring at the back of part 2 makes the whole difference between cycling and not cycling properly. I know you guys said that it should be a close fit and should allow the nozzle to easily travel int the bolt carrier but I went the other way around. I replaced with one o-ring with one I had laying around, now the nozzle doesn't move so freely in the bolt carrier but the cycling improved greatly (in the matter of cool down affect), it retracts fully in the BCG when it is in the forward position.

Now when I try to blow in the front of the nozzle (the bb side) whilst closing the lower hole where the mag sits, the air escape is less then noticable. When I tried that with the stock o-ring, the air easily escaped.

Now also there isn't an visible cloud of gas escaping out of the barrel.

This was all done dry firing indoors...field test is needed but I just got my hopes up because the cycling was very poor after a few shots before. This was much more of a problem using GHK mags than stock AGM mag.

 

@Luis

Just use windows movie maker and trim it a bit

Edited September 28, 2009 by mutikasha

[Luis21]

Yeah, that's very important.

 

If you decide to sand your o-ring down, make sure that you don't over do it. If the o-ring isn't sealing inside the bolt carrier then you'll feel less recoil and waste gas.

 

I would edit my video but then I'd cut out some important stuff.

 

-Luis

[snorkelman]

@luis idea is to fix it not to bodge it mine was already cycling it just wasnt doing so with any sort of worthwhile ROF in auto. A sanded oring might produce the desired result in short term, but is going to pickup and hold onto any contaminants, will break down quicker etc

 

@mutikasha the trouble with tight versus loose is it can be a toss up between better gas efficiency on one side, and waaay increased chance of the carrier sticking open (at full stroke the oring passes over the cut out on bottom of the carrier) leaving it bound up halfway inside the upper and halfway inside the buffer tube, or it simply skips retracting the nozzle at all on some cycles leaving blank shots The RAT is very prone to sticking open and the JDT/Ino snagged on me once already when i tried it with another oring

 

the original AGM forward assist works fine on RAT and Ino carriers - the notches are much more sharply formed than the ones cast into the AGM carriers

[Dom S]

Hey guys, this seemed like the right place to go to ask these sorts of questions...

 

Ive just ordered the following upgrades, for a completely stock agm gbb.

 

: CNC Aluminium bolt carrier

: Adjustable buffer (this is basically an NPAS, or so im told?)

: CNC aluminium hop chamber

: Steel Bolt Catch

 

 

 

Ok, so, assuming i put the lowest power setting onto the buffer, and run it on "abbey ultra" gas... what sort of fps am i looking at, UK legal? What about on 134a?

 

I will mainly be using it on semi automatic... Roughly how many shots would you say i can get, before "something" breaks?

 

Is it worth me not getting the steel bolt catch? Ive been told that if you get a harder bolt catch, then the bolt carrier wears instead. And obviously, this is alot more expensive to replace. What would you reccomend?

 

Have i forgotten any upgrades?

 

thanks in advance,

 

Dom

[colazel]

ebayabnned just release a 5ku cnc bolt

 

to many choice!! JDT, element, 5ku!!!!

 

also i want to know if the negative pressure nozzle style like the G&P incude an NPAS?

[Stealthbomber]

Is it worth me not getting the steel bolt catch? Ive been told that if you get a harder bolt catch, then the bolt carrier wears instead. And obviously, this is alot more expensive to replace. What would you reccomend

I'd never fit an aluminium BCG unless I was a ROF junkie who'd decided to disable the bolt-catch on all my mags.

Far better, IMO, to fit a steel BCG and then buy a few cheap bolt-catches and keep em as consumable spares.

 

One thing...

Depending how your tight o-rings are seating, you might be better off using a needle-file to file away at the seat rather than messing with the o-ring.

If you have access to the equipment (Snorkelman) you could use a lathe to reshape, and lengthen, the o-ring seat slightly and slope the seat slightly.

This should allow the O-ring to seat tightly on the compression stroke and that relax on the return.

 

[Luis21]

JDT Steel BCG review: http://www.arniesairsoft.co.uk/forums/inde...howtopic=174952

 

5KU magazine performance report up as well!

 

-Luis

[sacairsoftsn00py]

does anyone have experience with the element loading nozzle?

[Luis21]

does anyone have experience with the element loading nozzle?

 

I do, my hop-up setup hates positive pressure configurations. Also, the supplied Element pins don't fit the loading nozzle. I had to use AGM pins. Other than that, the construction is nice. A few leftover material here and there but it's easily ripped off.

 

I'll post more as I go on.

 

-Luis

[mutikasha]

does anyone have experience with the element loading nozzle?

 

Not impressed with the element nozzle. Pins that are supplied mostly don't fit, you could se some poor molding on the plastic (inside of the nozzle), and the nozzle tips are quite fragile. Also, they are default rigged for PPS.

Use AGM replacement if you want a cheap nozzle. I've got two of those replacement ones. They are not the same material as stock nozzle and hold up pretty well. I put a comparison pic of old versus new a few pages ago.

 

Has anyone’s BCG got so much wear from the bolt catch that is unable to function properly. My AGM BCG is showing wear, but it doesn't prograde any more and interacts with the bolt catch flawlessly.

 

 

[Pradal-Serey]

Does anyone tried to put the jdt aluminum loading nozzle in a agm bolt carrier? or similar, 'Im thinkin about those new bcg cnc'ed that showed up at ebairosft (vltor style & element cnc)

[t_hum]

Just finished the first stage of prototyping for the CrMo carrier this morning. Roughed it out of aluminum. Appears to fit very well. Overall weight of the 6061 aluminum prototype is about 100 grams with material to spare. Even at this level of material it feels extremely strong. The chromoly version of the prototype is next. Hopefully I can remove enough material to get the weight down around 200g. With such strong material making it very skeletal shouldnt be a problem. After that comes the nozzle. Ill post pics of the chromoly version as soon as its done. Im still waiting for a few tools to bore the blowback chamber to the proper size.

[mr.geo1024]

Today came to me JDT BCG and like Luis I just sanded o-ring down and now it shoots very well. ROF is about 4-5 (GG) and I use just GHK mags and haven't any problems.

 

Does anybody write his own FPS with JDT BCG? I haven't got chrono, so I'll know it after weekend.

 

And have another question - is it possible to use NPAS flute valve to JDT BCG?

[TheFull9]

Anyone got the Prime rear adjusting hop unit by chance? Mine is waaay over hopping every shot and the spring that should simply hold the adjustment piece in place is constantly pushing the adjustment all the way to the maximum; I'll cut it if needs be but I think there might be some trick I'm just missing.

[snorkelman]

never used that hop unit but spring applying max hop is the norm on the conventional WA hops (AGM G&P RAT etc) the barrel adjuster on those then counteracts the spring to reduce hop, so my guess is the prime style rear adjust is the same?

[snorkelman]

Does anyone tried to put the jdt aluminum loading nozzle in a agm bolt carrier? or similar, 'Im thinkin about those new bcg cnc'ed that showed up at ebairosft (vltor style & element cnc)

 

 

you cant as per previous posts amongst other changes its a 15.8mm diameter bolt while the standard WA design is 18mm or there abouts

[Luis21]

Today came to me JDT BCG and like Luis I just sanded o-ring down and now it shoots very well. ROF is about 4-5 (GG) and I use just GHK mags and haven't any problems.

 

Does anybody write his own FPS with JDT BCG? I haven't got chrono, so I'll know it after weekend.

 

And have another question - is it possible to use NPAS flute valve to JDT BCG?

s

 

I'd also recommend that you got to a hardware store whenever you have time and pick up some extra o-rings. It's good to have some on hand.

 

About buying a $15 NPAS flute valve and key. That will NOT work. I was also hoping it did but upon inspection, part #4 isn't threaded. That means it doesn't move forwards and backwards, without this FPS to blowback cannot be easily adjusted like on the NPAS. You can try shimming the flute valve manually though...

 

Also, a regular RA-Tech $60 NPAS will NOT work as well. Totally different design...

 

-Luis

 

[TheFull9]

never used that hop unit but spring applying max hop is the norm on the conventional WA hops (AGM G&P RAT etc) the barrel adjuster on those then counteracts the spring to reduce hop, so my guess is the prime style rear adjust is the same?

Not to worry, problem solved, turns out the rather brief and badly explained instructions that came with it combined with my general biff-ness was the problem, after all my cursing the thing it turns out it's actually a very ingenious little unit, heh. Being rear adjust it's quite a different design to the way the usual ones work; if they're all similar to the stock AGM that is, it's the only other I've seen.

 

Basically the actual lever that pushes on the nub is mounted pretty much the same as the stock unit, but instead of the rotating adjuster you've got a circular piece that goes around your inner, with a ramp cut in to it running in the same direction the barrel's pointing; so as this ramp moves back and forward along the inner it acts on the opposite end of the lever to the nub, pushing it up or allowing it to lower. On one side of this ramp piece there's a spring you slide between the inner barrel and outer constantly pushing on it, and a small screw piece on the other side that goes all the way through the hop unit, accessible when you remove the BCG, you just put an allen key in to the small hole in the hop and turn it one way or the other to allow the ramp piece to move back and forth as mentioned.

 

Probably not the easiest thing to explain, I'll try and snap a pic in a little while to demonstrate, suffice to say now I've actually got it working as it should I'm impressed with this thing.

[Luis21]

Yeah, that hop-up isn't the funnest to adjust since the feed ramps can get in the way but hey, at least you guys can run freefloat setups now.

 

-Luis

[snorkelman]

I think I see what you mean - screw on the breech face limits how far the spring at other end can push the ramp part along the adjuster?

[snorkelman]

as far as limiting the JDT FPS Id hazard a guess that the existing brass flute valve and return spring could be swapped out for plastic AGM one with ts lighter spring - chop down front of the AGM one it doesnt need to be as long, leave the back of it intact. You can then shim it to sit further forwards same way you could on an original AGM one (the rear of the JDT one is flat nowhere to place shimms against)

 

If you've access to a lathe alternative would be to turn a new castle section - shoulder cut further back, rear of it extended as a threaded tube and a matching thread cut internally on the steel ino bolt - effectively your own adjustable NPAS All its missing then is an RAT flute valve with the two prongs at the rear to screw the castlated section in and out