Double Feed/Mag Dumping Issue - Need Nozzle Data
 

I am working on a gun and it seems the main problem is the nozzle isn't moving deep enough into the hop up unit to block BB properly in the cycle and it's causing double feeds, and sometimes will even let the whole mag spool out.

Before I tear the mechbox down I started to wonder on if the wrong nozzle had been installed by mistake by the previous owner.

I have researched and found that nozzles are gun (not mechbox version) specific, but there isn't anything in the stickies that outline what nozzle is for what, or what the dimensions are.

It's and M4, with what I think is a G&P metal hopup unit. I have taken the upper off and can see that the hopup is not stopping the nozzle short, or interfering in any way. The hopup when installed is seated tightly to the mechbox, with no gaps or play. But the nozzle cannot be observed when looking into the magwell.


QUESTION 1 : Anyone here have an M4 nozzle they can measure for me so I can see if this is one from another gun? Or can someone link me to the data?

QUESTION 2 : I am pretty sure the nozzle simply isn't long enough. But is there something else (like gear timing) that could stop the nozzle from traveling fully forward?

Thanks In Advance!

BT

1. The one I have sitting here is 21mm end to end, +/- 0.5mm

2. Can't think of any. What's the condition of the tappet spring?

Thank bro. I'll tear it down and take a look.

you might aswell also change the nozzle, they sell on airsoftparts.ca for 9-10 $

Here's the real question: What is the brand of gun? From my experience, the nozzle isn't just gun specific, but is also hop up type specific in some cases.

Your saying the hop up unit is a G&P metal one reminds me of Apoc's G&P SPR that i set up for a high powered counter sniper gun. Since it had G&P everything, I replaced some or the seal parts and put in a 150fps spring, air seal nozzle, different piston, etc. Predicted I would get around 490fps out of it, but only was getting 420ish. Nutshell, the G&P nozzle in the gun was metal and had a square end on it. What I installed was tapered. I put the stock metal one back in, and the fps went up to 480ish.

Now, not that I'm saying this is the cause of the problems, but is food for thought. Double feeding to my mind indicates an issue with the hop up unit, such as split C-clip (that holds the barrel and hop up unit together), etc. Could possible spill an entire mag too if bad enough. Maybe check the hop up before dealing with the mechbox, it could be the nozzle is the problem, or the nozzle and hop up unti not working properly together (hence my above blurb on the SPR)................ hope that at least puts a few ideas in your head, Brent.

OK. I took another look at the gun and guess what. I cycled it ONE MORE TIME after leaving on the workbench and the nozzle extended all the way out. In that position is properly blocks the BB path in the hopup.

Of course the next time I cycled it, it only came back out partially.

I tore the box down and from what I can see, I have an upgraded bevel gear with more stops than the standard bevel gear for the anti reversal latch to catch on.

It seems the gear set is getting stopped past the point where the tappet plate is fully forward, but before the teeth on the sector gear are engaging the piston. Because it advances to that point, the tappet plate is engaged and it pulls the plate and nozzle back just enough so it can't properly bock BB's in the hop up unit.

I adjusted the gear set, and was about to test, when one of the motor connectors came off.

Hopefully this is just a timing issue. I think perhaps the gears slipped at some point and threw the timing off.

I will test it out tonight once I get a new motor connector and report back.

There is no gear timing. It sounds like your problem might be from the hop-up letting too many BB's through at once. On a lot of upgrade guns, the gearset tends to carry some momentum after each shot, therefor keeping the nozzle pulled back slightly. If your hop-up rubber is working properly, only 1 BB should sit in the chamber. It is not really the job of the nozzle to block the BB's.

Try Turning your hop-up all the way up. This might block extra BB's from coming through. If it doesnt double feed when you do this, then you know what the problem is.

Yah... I know there is no such thing as timing but every time I say that someone starts a 35 post argument :D


Hop up is all the way up.

I was under the impression that it only held one back, and the nozzles forward position kept the rest of the BB's in the tube ready to go. On all the animations that I have seen (and on all my other guns) the nozzle is forward, draws back, lets in a bb, then drives one BB forward to the hop up.

i hate to toss in a suggestion that may be expensive, but consiter a mosfet trigger, or better yet a trigger-master (with active motor breaking)

this may help getting your nozzle all the way forward and stop preventing a mag dump.

I was looking at that option.

At this point I may have to disagree on the gear timing thing.

The bevel gear has more tightly spaced backstops than a standard gear. I can adjust the position of the gear relative to the other gears so that when the anti-reversal latch is engaged, the tappet is in the proper position. If I move it a couple of teeth forward so that the next anti-reversal stop is engaged, the tappet plate is it then engaged b the pin on the sector gear and is pulled back, putting the nozzle in the "half-way" position.

This of course only has any impact if the nozzle is truly irrelevant in the process of holding BB's in place.

If the nozzle stops the flow of the BB into the hopup, wouldn't AEGs with a really low ROF have double feeding issues? I thought the flow of the BBs into the hopup is stopped by the fact that the hopup unit could only accommodate one BB in the ready-to-enter position.

How's your hopup sleeve? BBs shouldn't be able to roll right through lipped end.

OK. picture this..

Your nozzle doesn't proceed past where you can see it when looking in the magwell.

You slap in a mag, BB's pop straight up and hit the top of the hopup. They can't go backwards because the nozzle blocks them, so they roll forward till they hit the hop up.

Now on my hopup, there is room for at LEAST two BB's between the hop up rubber and the nozzle, maybe three. (But only if the nozzle is half way back, full forward there is only room for one BB)

When that nozzle comes forward, there are gonna be 2 or 3 BB's flying down the barrel.

See what I mean? If the nozzle doesn't play a part in the process, then I would have had double feeds since I bought this gun and I haven't.

Well, if you get desperate enough, here's one way I've heard to deal with too many BBs working their way into the hopup. Take a round sanding bit and sand/drill a slight indent right down the mag-to-hopup feedpath, into the ceiling of the nozzle-to-hopup feedpath. If done correctly, that'll "seat" the first BB coming up from the mag and prevent his friends from joining him.

Your earlier posts make it sound like your tappet plate isn't moving all the way forward; can you confirm that the tappet plate spring was installed?

- After reassembling the mechbox, push the nozzle backwards and see that it springs back forward and isn't jamming. Sometimes on my m4 - depending where the gears are in the cycle - it won't let me push the nozzle in manually but always will after I've closed the mechbox and the tappet cam is at the 1 o'clock position.

- Check to see the hopup/rubber is all installed properly.

The only time I've seen double feeding is with guns where they have vitually no hopup on - adjust it properly and it blocks the other BB's from following up into the chamber. A good rubber you will need to slightly push the BB into it - good check before you install one.

Sounds like you understand how things work (ie. no gear timing, how BB's actually feed etc).

Just measured an unknown m4 nozzle I had (believe it's a stock CA) and it came to 20.68mm (I used a digital caliper).

Yes, it's in place and feels like new. Very strong. The tappet does look like it's either worn or custom however. It's not flat, but has a cut out where the pin on the sector gear hits it and where it hits the shat for the sector gear. I will take some PICS tomorrow when I tear it down again.

No issues at all, the only time it won't go all the way forward is when the gears have move to the point where the pin on the sector gear starts to pull the tapet back. Note that this is the position the gun stops in 99 times out of 100, and is the position it's in when I tear the box down.

Will be checking that tomorrow. I have parade tonight.

I did check this. The bump is clearly visible at full hop, and I can press on the bump with a plastic bar, it doesn't move and stays down with pressure on it. BB stops no problem, and I can't blow it through the hopup when it's on full.

I have learned that I will never know everything about these damn things. For something that doesn't have that many parts, it has more complexities than a fricken woman. :D

Has anyone thought of the spring on the tappet plate? Is it worn, twisted, stretched?

Nice and strong, in my first response above. :D

Actually so strong I think it might be wearing the tappet unnecessarily.

the hopup rubber is what prevents mag dumps. the nozzle blocks the next bb from entering the chamber only while its acting on the round that has already been chambered. when it retracts, it allows one in, and the hopup rubber should stop it. turning the hopup up is not the solution, as the nubbin is downstream from the problem.
if you're getting double feeds, the nozzle is the secondary culprit... the hopup rubber and/or hopup assembly would be the primary. any remaining culprits would be inside the mechbox.... deformed/cracked/malfunctioning or wrong tappet plate or spring, followed by gear or anti-reversal latch problems.

things to keep in mind: the nozzle will not always rest in the same place after firing. where it lands depends on where the anti-reversal latch catches the bevel gear.
you CAN'T have a timing problem if the mechbox cycles - it resets every round.
an improperly sized nozzle could allow a second bb to enter the chamber, forcing a double feed, but a scenario that is more likely would be that your particular mechbox in that metal body combined with that particular front end and that particular hopup and that particular rubber and nozzle is causing an excessive gap, allowing double feeds and mag dumps.
you see, the one thing that TM had going for it was that those plastic molds were the frikkin same every single time, and they had their mechboxes dimensions down to a science, so these problems never existed untill foreign parts were intorduced into the mix. now you have this metal body, that metal front end, some other hopup with an aftermarket rubber and endless combinations of aftermarket mechbox parts that combine to make one big headache.
Looking back at your problem, the solution seems simple. get a brass barrel, and a bag of bb's. load a bb and put the barrel in your mouth. aim and blow hard. this should provide more consistant results.
:D

LMFAO!

Roger that brother. It's obviously a sick gun, so I will fuck with it till I get it working LOL.

Two blown bearings, causing all sorts of fucking havok. It's my own fault. I missed it on my initial inspection because I thought I knew what was wrong with the gun, I narrowed my inspection and didn't tear the box down completely. I actually did'nt know the bearing was blown till I was setting the gear down and dropped it about 2 CM to my benchtop. Fucking ball bearings when everywhere.

That's it. This is the third tme bearings have blown on this fucking thing. Back to bushings.

Here is a picture of the tappet. Does this look overly worn to anyone?

http://tactical.blackthornegroup.ca/...cs/tappet1.jpg

http://tactical.blackthornegroup.ca/...cs/tappet2.jpg

ya thats done dude!

here took a pic of a used one i had....

http://i539.photobucket.com/albums/f...appetplate.jpg

Looks more "fucked with" than worn! Lol, that's very likely the issue you are having. And bearing bushings suck huge ass!

Worn, yes. Enough to make the gun not work? Probably not.

I wouldn't say that the part i circled prob wasnt loading the bb's right.

http://i539.photobucket.com/albums/f...ar/tappet2.jpg

What size of bearings are they and what type of spring are you using?

7MM and no idea on the spring. It's got tighter rings at one end, and is baby blue.

Do you know what fps it's shooting?

OK. Went to bushings and a new tappet plate and guess what? The damn thing works. I just need to re-shim it so it's a touch looser and I will be good to go.

Oh and to everyone in this thread that stated that the nozzle doesn't stop the BB"s from entering the hopup, it does on both our guns (once they are working properly :D )

Just like in this animation:

YouTube - version 2 gearbox animation