AGM M4 GBB

[TheFull9]

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?

After re-reading my shockingly poor description of it I'm impressed anyone managed to actually realise what I was talking about; but yes that is exactly the system. It's a shame I'm going to make this in to an L119 and hence it won't ever see a free float or 203, but on the other hand the compatibility with AEG barrels and buckings worked out really well. I also think it's got good potential to hold it's setting better than the standard design, especially since you could put a bit of thread lock on the adjustment screw if you wanted.

 

I'm going to give it a shoot test tomorrow morning, I've got a madbull 363mm tightbore along with madbull bucking and H nub in there, I'm pretty positive that I'll get some good results out of it. The only thing I'm missing is a chrono for the NPAS, what should it be doing to a coke can if I manage to set it to ~300 FPS?

[Ion]

I'm going to give it a shoot test tomorrow morning, I've got a madbull 363mm tightbore along with madbull bucking and H nub in there, I'm pretty positive that I'll get some good results out of it. The only thing I'm missing is a chrono for the NPAS, what should it be doing to a coke can if I manage to set it to ~300 FPS?

It should generally go through the first side and dent the second side.

[TheFull9]

Cheers, I'll get it as close as I can to that and give it a test. Only have my garden to fire down which isn't too long unfortunately, but we'll see what happens. Report should be up within an hour or two.

[teflon don]

does anybody know how long the barrel from the stubby killer is

would a ratech s barrel fit 250mm

[Luis21]

does anybody know how long the barrel from the stubby killer is

would a ratech s barrel fit 250mm

 

Well the stubby killer has a 7'' barrel. That converts into 177mm. So no, the RA-Tech 250mm barrel will not fit, it will stick out. That barrel is meant for 10.5'' barrels(ie. CQBR).

 

-Luis

 

[teflon don]

thanx so what barrel would you recomend for a stubby killer

 

7inch isn't that the length of the outer barrel ?

177mm is that with or without flash hider

Edited September 30, 2009 by teflon don

[Luis21]

thanx so what barrel would you recomend for a stubby killer

 

7inch isn't that the length of the outer barrel ?

177mm is that with or without flash hider

 

You can get an AEG barrel and rubber compatible hop-up chamber and buy an MP7 inner barrel. Those are 182mm, only 5mm longer than the stubby. The flash hider should cover it.

 

-Luis

 

[teflon don]

thanx luis

but its for a friend of mine who wants every thing as realistic as possible

and the idea the a inner barrel is visible would make him cry

if someone has first hand experience with upgrading a stubby killer let me know

[Luis21]

thanx luis

but its for a friend of mine who wants every thing as realistic as possible

and the idea the a inner barrel is visible would make him cry

if someone has first hand experience with upgrading a stubby killer let me know

 

No problem. You can also buy the gun, measure the inner barrel, and then call up edgi and get a custom made inner.

 

-Luis

 

[Frakk2k]

I tried to install some Magpul XTM , but it seems the rails on the AGM isnt standard size. I could only fit 2 of 4 panels on each side. Anyone else had problems like this? It just gives me another reason to get a new front end.. Perhaps a new DD MK18 front before christmas.. ?

 

I also bought this: http://www.ebairsoft.com/element-ex060-piv...eed-p-2551.html - and my advice, don't buy it. They don't fit, and if you do manage to squeeze em trough, there is no way that could be called SPEED PINS. Poor workmanship on em aswell.

Edited September 30, 2009 by Frakk2k

[Luis21]

I tried to install some Magpul XTM , but it seems the rails on the AGM isnt standard size. I could only fit 2 of 4 panels on each side. Anyone else had problems like this? It just gives me another reason to get a new front end.. Perhaps a new DD MK18 front before christmas.. ?

 

I also bought this: http://www.ebairsoft.com/element-ex060-piv...eed-p-2551.html - and my advice, don't buy it. They don't fit, and if you do manage to squeeze em trough, there is no way that could be called SPEED PINS. Poor workmanship on em aswell.

 

The AGM tolerances aren't the best. Sometimes you have modify the gun.

 

-Luis

[TheFull9]

Okay, it shoots, progress is being made. I'm happy to say the hop unit it working and I'm able to adjust it and get nice flat trajectories within the limited range I have (about 25m), I could almost take it to skirmish, there's just (hopefully anyway) one last hurdle, and I'm pretty sure it's with my GHK mags. They quite often seem to be mis-feeding a bb, I'm not sure exactly what's going on when it does this, but a round will somehow fall to the side somewhere on top of the mag and stop the bolt going forward, meaning the next time I pull the trigger all the gas vents; not good when you've only got 4x40rnd mags to last for an hour+ skirmishing. Demonstrated here:

 

 

And again here:

 

 

For a while I was thinking it might be the mag getting cold from all the auto firing, but 3 out of my 4 mags all did this in one shooting session after being taken from my room and simply filled up and left for around 5 minutes before firing. Ambient temperature was definitely above around 23-4C I'd say. Anyone have any thoughts on which part/s might be causing this to happen so frequently?

Edited September 30, 2009 by CKinnerley

[Luis21]

@CK:

 

It's definitely a feeding issue.

 

Your gun is double feeding. I say it's the GHK mags. The mags are letting 2 BBs go at the same time.

 

Your loading nozzle face is loading one BB and the other is getting in the way, stopping your loading nozzle from going all the way forward and lining up with the magazine gas port.

 

Since the loading nozzle isn't aligned with the magazine's gas port, the gas cannot cycle the bolt carrier group backwards. Then the gas has nowhere to go and it vents.

 

If the BCG was blowing back then it would be able to re-cock the hammer and relieve the pressure on the mag's gas release valve.

 

Again, the double feeding is doing this. It's most likely due to the mags. Check for mag movement inside the magwell. See if pushing up on the mag helps, I've heard it's a problem with GHK mags.

 

Also, try using your stock AGM mag and see if the problem persists.

 

-Luis

[Stealthbomber]

@CK:

 

It's definitely a feeding issue.

 

Your gun is double feeding. I say it's the GHK mags. The mags are letting 2 BBs go at the same time.

 

Eh?

[TheFull9]

Hmm.. could've sworn I'd posted after luis. Anyway, the AGM mag has a very minor leak but I'll give it a go tomorrow just to see if it does the same, good enough process of elimination at least. It's hard to tell if it's double feeding or just mis-feeding at the moment, I can't remember whether I was finding one round loose in the receiver and one in the hop-up, or just one floating around loose, again something on the list to check tomorrow. The metal lips on top of the GHKs at the back seem to touch the lower edges of the upper when inserted, but I'll have a shot at pushing on them and see what happens.

 

I've had to do a fair bit of filing and work with the old wet & dry inside the mag well to get one particularly over-sized GHK to fit, but there's no sideways movement with any of them. A very small amount of back and forth rocking when locked in but it's pretty minor, so I'd imagine they are all seating correctly.

[tinydata]

Ckinnerly, the same thing is happening to me. The AGM mag works fine, even on green. No leaks, no jams, no venting. Then the GHK will do exactly what yours does. The guys at the local CQB course said it might be problems with the AGM nozzle, but I'm not sure. Maybe the GHK mag spring is too strong or something.

[shinhk]

Maybe a bb gets ejected from the mag after it cycles causing one bb to be released into your upper receiver. When the bolt flies back forward it gets jammed with the bb that was ejected. Try this: fire each shot while holding your bolt stop button down. Force it lock back after each shot to see if a bb is getting shot out of the magazine after you fire.

[sacairsoftsn00py]

use larger diameter bbs...

 

which brand of bbs are you using?

[shinhk]

use larger diameter bbs...

 

which brand of bbs are you using?

That could work too...however the remedy to the problem of stuck bb's in the ghk mags before were to use smaller diameter bb's. Using larger diameter bb's to solve this problem may bring the other problem back up.

[sacairsoftsn00py]

i have never had issues with my ghk magazines when i ran airsoft elite .25g bbs through them....

 

 

[Luis21]

I see that you're using an NPAS BCG. Right?

 

If so, make sure that the nozzle stays screwed in all the way and that it doesn't come unsrewed during firing.

 

A nozzle that sticks out further than the small stud(the one that loads the BBs) on the loading nozzle is a bad thing.

 

-Luis

[TheFull9]

Maybe a bb gets ejected from the mag after it cycles causing one bb to be released into your upper receiver. When the bolt flies back forward it gets jammed with the bb that was ejected. Try this: fire each shot while holding your bolt stop button down. Force it lock back after each shot to see if a bb is getting shot out of the magazine after you fire.

Will give that a go and see whether I can notice it feeding more bb's than it should.

 

use larger diameter bbs...

 

which brand of bbs are you using?

Standard Excel 0.2s in there at the moment, but I'm just getting rid of them really before I move on to Madbull's. I've got a load of their Match grade 0.2s, Tracer 0.2s and 0.3s here I could try.

 

I see that you're using an NPAS BCG. Right?

 

If so, make sure that the nozzle stays screwed in all the way and that it doesn't come unsrewed during firing.

 

A nozzle that sticks out further than the small stud(the one that loads the BBs) on the loading nozzle is a bad thing.

Got the full RA Tech NPAS setup in there yeah, is the white plastic part in the centre what you're referring to?

 

 

It's sitting about 2-3mm below the front edges of the bolt splines.

[mutikasha]

Done some brainstorming today...Take in to the consideration that my AGM replacement nozzles came pre assembled.

Anyway, on part 10 of the nozzle there are supposed to be two o-rings, one for sealing the contact between the bolt carrier and the part 10 so no gas escapes during the cycle, and o-ring number 166 which came installed between the #2 part and #10. Why is this here??? Done some thinking, and couldn't think of any reason that this should be here. In the stock setup I tried to blow air in the part of the nozzle where gas flows from the mag to the nozzle while pluging the nozzle tip. Doing this in the stock setup there is a minor gas escape trough the front par (#19 o-ring not sealing propperly) and lot of air escapefrom the back of the nozzle trough the carrier.

After doing this I removed the #166 o-ring an put it also on the back of the #10, put a bit larger o-ring as a replacement for #19. After this no air escape at all! Cycling improved (continuous cycling without the loss of ROF time)!

I'm amazed every time at how this system is full of design flaws.

Filed test needed - tested only dry firing indoors. Also switching from Abbey Ultra Predator as it is utter *suitcase* to Red (green?) gas 13.

 

Somebody earlier said that his PPS setup isn't working anymore after cutting down the flout valve...this is a no surprise because the valve needs to stick a bit out of the nozzle so, a bb can push it back in the nozzle and set in in the open position. No cannonball bb or magical force will push the bb out of the barrel if the valve is trimmed using a PPS setup and thous set in the closed position or full blow back setting.

NPS system is a whole other story

 

On the GHK mags discussion...never had any problems with mine in view of bb-jams and stuff like that. Try using some quality and heavy bbs. Gas system lets you use these and it was the one thing that brought me to gas riffles (other than being the coolest and most realistic things in airsoft ). If your down for a RA tech NPAS BCG then get some money into quality bbs - this is the thing that will screw up your gun performance even if everything else is mint.

[Luis21]

@CK:

 

Yes, the white, screw-in, nozzle is what I'm reffering to. Make sure to find a way to keep it in there. If you have any aluminum ones around, use those and loctite it in there. You can you use crazy glue with the plastic ones if you plan on keeping it plastic. Don't overscrew the plastic nozzle, the the threads break easily.

 

During firing the white nozzle comes unscrewed all the time. If it hits BBs while extended out then you'll risk breaking it. Make sure it stays screwed in.

 

-Luis

[TheFull9]

Did some more shooting and experimenting over the course of this afternoon. Trying the stock AGM mag, encountered no problems and interestingly it locked the bolt when empty, possibly due to the RAT replacement catch, hard to say. The hop unit is way over hopping again, I think the vibration when firing is possibly moving the adjustment screw, I've got no loctite at the moment but I think putting something in there as a spacer should adjust it well enough for now.

 

Next went on to the GHKs with madbull 0.2 match grade ammo, didn't get any of the jamming, though I only had time to go through 3 mags worth... on the other hand based on previous performance 3 mags would have definitely brought up the problem before, so it looks like it could be just the ammunition. The other problem that came up however was the bolt catch, would engage occasionally at entirely random times when I was nowhere near empty, will have to have a look in to this.

 

Overall, taking everything in to consideration, I'm thinking getting some Bomber mags might be the way to go forward.