KWA M4 misfeeding.

[Ichkabible]

Hey guys, so I am working on a KWA M4 S-system for a friend of mine, and I am having misfeeding issues. So, it has been mostly rebuilt, he put 16:1 gears in it so I put a sector delay clip in it to prevent this but it's still happening. I've re-shimmed, re-greased, corrected angle of engagement with Sorbo, polished the cylinder, put a little silicone around the cylinder head, filed down the front of the tapper plate, r-hopped it, prommy blue straight bucking, mosfet, and re-wire. Any ways I'm thinking it's probably the nozzle being a little long since that's new too, but I'm unsure how much to file off if I do that.

It's shooting at about 1.4 joules when it does shoot and it's pretty consistent so far. The mags i tested are classic army and a VFC (which was really tight, no surprise). So this has that hop up that splits when you break down the gun and my friend who is the previous owner of the gun noticed some small peice missing but he isn't sure what it does and neither am I since I've never seen it (buddy gave me a box full of parts including the compleatly dismantled gun, and told me to fix it so that's fun. Can't find the part anywhere) apparently it's "a springy plasticy bit." Great discription, it's probably important. Is there a way to switch to a prowin, or should he get the same replacement part.

[Crowin]

It might be the hopup tension spring. Here is a picture of a hopup with one
http://www.evike.com/products/43118/
The prowin hopup uses a set screw instead i think. If you replace the hopup get one of similar design.

That being said it is probably the nozzle. I would try and shim the hopup forward from the gearbox if you can first, before sanding the nozzle down. I used a very thin shim over the back of the hopup before it goes in to the gearbox. But caution this can miss-align your mags and give different feeding issues.
Also make sure your tappet moves freely, this can also cause feeding issues if it is binding in any way.

Hope this helps.

[RainyEyes]

Originally Posted by Crowin

That being said it is probably the nozzle. I would try and shim the hopup forward from the gearbox if you can first, before sanding the nozzle down. I used a very thin shim over the back of the hopup before it goes in to the gearbox. But caution this can miss-align your mags and give different feeding issues.
Also make sure your tappet moves freely, this can also cause feeding issues if it is binding in any way.

Hope this helps.

Op literally did everything except mod the nozzle which is the prime suspect in misfeeds.

File down the nozzle so that it is tapered. Look down the barrel once it is safe and see if the barrel and the nozzle are aligned.


Etc etc.http://www.airsoftcanada.com/showthread.php?t=169828

[Ichkabible]

Originally Posted by Crowin

It might be the hopup tension spring. Here is a picture of a hopup with one
http://www.evike.com/products/43118/
The prowin hopup uses a set screw instead i think. If you replace the hopup get one of similar design.

That being said it is probably the nozzle. I would try and shim the hopup forward from the gearbox if you can first, before sanding the nozzle down. I used a very thin shim over the back of the hopup before it goes in to the gearbox. But caution this can miss-align your mags and give different feeding issues.
Also make sure your tappet moves freely, this can also cause feeding issues if it is binding in any way.

Hope this helps.

Thanks. It's not the tension spring, after doing some research it actually looks like the part may be just outside of the hop up, and it is a small price of plastic that is springy. Not a spring, sorry I gat a terrible description from my friend, he wears the pants on his head sometimes. Now because it's a two piece hop up, I wonder if shimming it would work, the bottom half of the hop up is screwed in to the lower receiver so it will not move. So I guess that really just leaves filing the nozzle. Thanks for your help 👍🏼

[Ichkabible]

Originally Posted by RainyEyes

Op literally did everything except mod the nozzle which is the prime suspect in misfeeds.

File down the nozzle so that it is tapered. Look down the barrel once it is safe and see if the barrel and the nozzle are aligned.


Etc etc.http://www.airsoftcanada.com/showthread.php?t=169828

So that being said I just want to make sure I don't file down too much or it won't seat in the bucking properly, and I gotta get the taper right. How should I do the taper? This is the first time I've had to do this on a gun.

[Ichkabible]

Originally Posted by Ichkabible

So that being said I just want to make sure I don't file down too much or it won't seat in the bucking properly, and I gotta get the taper right. How should I do the taper? This is the first time I've had to do this on a gun.

I just read up on the link you sent, I missed it the first time. Thanks!

[Nathan.g]

Okay, every kwa I have ever owned or worked on seems to have this problem. I fixed it in all cases but the reasons causing the issue differed.

I agree that this isn't a gearbox issue. A protein hop up will not work, nor will any aftermarket hop up. The only one that will work (without a crazy amount of modification) is a stock plastic kwa hop unit.

In my experience, this is not nozzle related either; it's the outer barrel itself. It didn't seem like it but it was pressing the hop up so hard on the gear box that the hop unit was bending outwards and creating a lip which was causing feeding issues. Other times it had something to do with my bucking; rebuild the barrel portion, change the nub, and make sure that the bucking is seated properly.

Try just holding the barrel in place with no upper. If it fires, 100% it's outer barrel related, if not, then it's bucking.