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KWP

AGM M4 GBB

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Been toying around for a few months on and off regarding putting a small piston inside the nozzle. My point being that recoil gases used is too much for the WA system. Adding a piston inside the nozzle to push the BCG back would dramatically reduce the gas consumed on blowback.

Finally was able to do this with success, highest reading so far on .2 is 450 fps, can probably up the readings by using a stronger flute valve spring. I can also finish 30 rounds easily on one trigger pull! After 30 rounds there is still enough gas inside for another load of BBs.

Cool down is not as bad as stock setup since I do not need a lot of gas per shot. The only drawback is BCG does not cycle fully rearwards so no bolt lock function. Also recoil is quite tame comparatively.

 

How does the blow back feel? I also toyed around with steeling the NS2 style gas system and hijacking it for the WA system, but without access to a machine shop to make new bolt carriers and nozzles it was a dead end adventure. I still have the ideas rolling around in the head of mine, but I'm not sure how much it truly matters :P

 

I'm curious to see how you did it?

 

As for the Big Dragon (READ: ENERGY) High flow Valves, give them a miss.. the shafts on them are too long to cycle correctly with a 150% hammer spring in my WOC and WA mags, and the ones I cut down with the mill either runaway firing or double tap every time. Stock WA valves are fine, just need to find a source for good quality valves... How do the AGM valves compare to WA valves (Read: How does an AGM mag compare to the WA Mags in terms of felt blow back and FPS?)

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nozzlemods-1.jpg

 

Here is the internal brass piston that I had made for the nozzle, head has an o-ring and rod actually pushes the BCG backwards instead of gas. Although expanding gas actually does the work in pushing this piston, this setup saves on gas and there is no need to fill the insides of the BCG. Also modified the inner part of nozzle where large o-ring sits, this acts as guide for piston rod. There are several other things to me done before everything works perfect.

This is just one way of modifying the nozzle, I can think of another where whole nozzle is thinner and has a smaller o-ring at the back. BCG has to have a sleeve to fill the void though.

:)

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A true masterpiece!

Drawing with dimensions would probably earn you some eternal gratitude from the WA GBBR community. Hint hint.

 

wink.gif

Ferch

 

 

Took me a couple of months of figuring out, experimenting, not to mention several failures before it finally worked flawlessly.

As for giving out the actual dimensions and solutions to niggles, hmmm.

Let me think about it. geek.gif

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I've been pondering...

 

I want to convert the AGM M4 I have into a gas bolt action rifle. So you have to manually cock it every time you fired. Sniper rifles aren't allowed here with semi- or full auto functionality or you'd have the AEG specs enforced on it.

 

So I was pondering on how this could be achieved. Is this possible ?

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You are referring to the metal thing behind the sear that is connected to the fire selector ? But it will be semi-auto and not manual cocking, right ?

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Correct sir, sorry I did not fully comprehend your first question about the bolt action requirement. Anyway since you require a bolt action rifle, then what you can do is take out the flute valve inside the loading nozzle. This will still move your BCG (Bolt Carrier Group) rearwards but may not be enough to cock the hammer and even load the next round, hence necessitating to pull the charging handle fully everytime.

Although taking out the flute valve dramatically increases your fps, so you may need to use a lesser gas like 134a to be playable.

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It did increase power, but it's still shooting full-auto and semi-auto correctly. Strange as I didn't expect this.

 

I removed the circled pieces (along with a spring):

 

wa_bolt.jpg

 

EDIT:

 

I also removed the disconnect, you do mean this part, right ?

 

wa_disconnect.jpg

 

It actually also didn't make any difference. Still fires full-auto and semi-auto.

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The parts you removed is correct and are the ones was referring to. Actually am not that much surprised since we have discovered that taking out the flute valve in some cases would not have any effect on the normal cycle of the gun. I believe that in some cases the sealing inside the BCG and loading nozzle is tight, meaning you have an efficient setup - hence BCG still cycles. Have you tried using only 134a gas? This may be too weak to fully cycle the BCG.

 

OT: Not wishing anything bad to your gun but the stock charging handle of AGM is pot metal, you may eventually break this since you have a bolt action rifle setup.

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I tried it on 134a and it cycled properly, surprisingly crisp cycling too ! If I use propane, I might shoot way too hot probably. Good tip about the charging handle ! Must remember that. When I'm getting this bolt action thing sorted, I'll make it a decent project with a new stock and barrel.

 

Is there anything else I can try to stop it from recocking/cycling ?

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Seal the rear area of the nozzle maybe? Get some kind of putty or a small block of material you can glue in to place that'll block the channel where some of the gas would normally travel rearwards to cycle the bolt.

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The gun cannot be converted into a bolt action since it is GBB.

 

If you eliminate the blowback cycle then all the gas in your magazine will vent since the hammer will still be dropped and the bolt carrier will not cycle and re-cock it. Even if you manually cycled it right after pulling the trigger, loss of gas would be too great and there will be no consistency whatsoever due to cooldown.

 

If you want bolt action then NBB is the way to go.

 

-Luis

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Oh damn, yeah...

 

My AGM was always doing that when it jammed, vented all the gas in the mag in less than a second without the bolt moving to reset the valve. Don't know why I didn't think of that, sorry Phuncz, I think you're a bit stuck with this one.

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OK if it can't be done, it can't be done. Removing the flute valve solved atleast some of the problems I had with the gun, so that's a big plus. And putting in the disconnect is a 2 minute job.

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I believe it can be done because that was my problem before, my gun not cycling properly. My agm sans flute valve was running 640 fps on propane, but bcg travels only a few cm backwards, not enough to cock the hammer let alone loat a bb round. Experiment with using a smaller o-ring at the back of loading nozzle. This will make your setup less efficient since it vents some blowback gas out of the chamber and pushing the bcg less backwards. It may not be optimal but at least you have a bolt action rifle in the end. Another thing is to add a spacer on your buffer tube, or make the buffer spring stronger. This will give more resistance to your bcg going backwards as well.

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OK So I tried some various things, I found out that a AEG cylinder would just about fit inside the buffer tube and the recoil piston's head is the same size. But this lead me to the idea of using an AEG spring and piston, which fits perfectly. Only problem is that some might have issues with the buffer lock (being too short), but it wasn't a problem for me.

 

Anyway, I tested it with parts those from an M4A1 AEG I had that destroyed itself, it shot little above 360fps to have an indication. The spring is a lot stronger than the standard recoil spring and manually cocking it is pretty tough. It will eventually lead to the charging handle breaking with the force needed to cock it and the buffer lock because of the multiplied recoil it now gets to endure.

 

But it kept cycling perfectly !! This is madness ! I've had so much problems getting it to cycle propperly in the past and now I remove and change critical parts and it keeps on going. For how long is another tale but this gun is useless to me anyways as it is/was.

 

 

So we've found out that making the recoil a lot tougher only gets me a very crispy recoil and very fast ROF, instead of it giving me my much desired manual operation. So the next best thing to try to get it's efficiency down by replacing the O-ring.

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You're not the only one who is stumped. I put more than the price of the rifle in upgrade parts just to have a usable full-auto and the the things I did to "break" it's full-auto is actually enhancing it. What's next, it'll recycle vented propane ? Then again, I'd probably not have a good seal at the loading nozzle if I kept the original parts. But it still baffles me...

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