Shooting multiple bbs on auto at once
 

I just finished installing a systema 120 mechbox in my m4. It barely fires on semi, the first pull only bring the nozzle back about half way and does nothing, and the second pull completes a cycle and the nozzle kinda goes back and forth a bit after. On full auto each cycle is shooting like 2-4 bbs. I'm using a 1500mah 9.6v battery and a eg1000. Any ideas on whats wrong?

Is it the AA sized small cell battery? They have pretty shit output.

As for double feeding, it's likely your hopup / gearbox nozzel connection, or the hop up rubber. Start by putting a couple of drops of 100% silicon oil in the loading hole of the hopup.

As for the half cocking, try a larger battery. The spring may be too hard for the small cell mini battery to pull.

http://brotherprice.com/ebayphoto/Fi...%20battery.jpg

Thats the battery, and I'll try some silicone on the hopup.

Is this a NIB Systema mechbox? Or did you modify it?

I'm in Calgary

Yes it is a drop in, brand new m120 mechbox.

I tried a 8.6v battery as well, with the exact same effects, it seems to pull the spring fine.

When I was test firing the rifle was fully assembled.

On full auto each individual cycle sends multiple bbs out the barrel.

I observed the nozzle movement with the receiver separated with the nozzle clear of any obstruction.

Hope this helps a bit more.

something wrong with your hop up unit + magazine

what body/make of rifle did you drop this into?

I'd also like to note that the fire selector was much harder to turn with the new mechbox installed, and doesn't click nicely on semi or full like it used to. Could the selector plate have anything to do with it?

And it's going into a stock tm m4 body.

Could wiring be an issue? Due to lack or current or whatever. I have the tabs that come on the wiring to the battery clamped on a section of wire witch attaches to the battery connector. The tabs on the wiring to the battery are the exact same as the tabs that hook up to the motor only not bent. Would it be better to but them off and just tie the two wires together? Or would this make no difference at all?

Poorly spliced together wiring is never going to help anything...

Not sure why you did it that way? If you need those types of spade connectors, you can get them (both the male and female ends) at Canadian Tire (automotive section...usually with the fuses). Get some shrink wrap at the same time to make a cover/insulator for the hook up.

The reinforced mechbox could very well be tighter in the lower compared to a stock TM mechbox. The selector plate is beefier as well. This would make the selector hard to turn/sticky. If you're forcing it to semi and then full auto...don't. You'll just wear or strip out the lever/disk. Try disassembling it and reassemble it...look for signs of where/what is rubbing (i.e. selector disk, selector plate, the left bushing of the spur gear, etc...).

Anyway...that still doesn't answer why you'd get multiple bbs with each shot.

So when you get it firing on semi (try moving the selector just a hair or two past semi), you get more than one shot at a time? No dry shots at all?

If so, then I'd guess that your nozzle has jumped off the tappet plate, the tappet plate is broken or your hopup/hopup rubber is broken.

Better see a gun doc at that point.

Mmm that sucks, and on semi one pull does a half cycle and the next does a full, then a half then a full etc... And I doubt my hop-up broke in the time it took me to switch gearboxes, because it worked fine just before with my old one.

Get the wiring sorted out and try semi again...once semi works, full auto will "automatically" work.

The hopups don't break from being used...they break from people reassembling their rifle and close the upper receiver down onto the lower without making sure that the barrel/hopup-unit is as far forward as possible. The "frame" of the hopup unit catches on either the nozzle or the top edge of the mechbox and snaps off. No offense to your competency...just internet-guessing.

When you get to your max frustration limit...do yourself a favour and take it to a local gun-doc.

Best of luck with it.

Hmm, even if the hop-up was broken it's still cycling wrong, i can see the nozzle spazing out when it's disassembled. On semi, that half cycle is loading bbs because on the full cycle it shoots about 3. Also I noticed the nozzle on my new mechbox extends to the far end of the feeding tube, where as my old TM mechbox has the nozzle sat before it. Is this just a difference in operation, or is that a problem?.

It sounds like you're really just grasping at possible problems. It's very frustrating for us to try and help you if you don't:

Take pictures.
or
Open the mechbox and have a look.

In the end, it's either going to take us seeing your issue, rather than you explain it to us; or you're going to have to have a gun doctor see it in person.

Sounds like a tappet plate problem like was said. Is the nozzle even connected to the tappet plate anymore? Is it loose? Can you push it in and pull it out without any force?

I was just thinking, if the tappet plate spring broke, it would show these symptoms. No?

Yup. Or if the tappet broke or the nozzle is somehow off the tappet plate.

Time to stop pulling the trigger, and start opening the mechbox. Bring a camera. :)

Strange that a new-in-box Systema mechbox has broken parts though, if that's the case.

Last post from me on this one...

You, no offense intended, seem to be having a hard time figuring this one out. And all the advice you're getting is good, but pretty much just guessing since nobody but you can see what's actually going on.

You've got a great mechbox there, in a great rifle, and it's got a pretty stiff spring in it. You're going to be pretty close to opening up the mechbox next to figure out what's wrong...and if you haven't done that before it can be a bit dauting the first time. It'd be a shame to mess it up and potentially toast a good mechbox.

You may want to give serious consideration to getting a gun doc to check out the mechbox/rifle for you. Hopefully it was something as simple as a jam that forced your nozzle off the tappet. It may very well be a simple fix, but if not, that person should have the experience to draw on to fix it right.

Don't get me wrong, I'm a huge proponent of guys working on their own stuff...but grab a not-so-expensive mechbox to learn on and don't risk your multi-$$$ one.

Again, best of luck, hope it's up and running quickly!

Tys

Hah yeah, I'm not going to open this mechbox, tappet isn't broken the nozzle is springy pushing in. I'm not going to do anything that would break something vital, i did just un-install and re-install everything so I'm going to see if this works out. Thanks for the help anyways guys it's much appreciated =D.

The tappet can be broken and the nozzle can still be springy. Most tappet breaks occur near the sector gear.

Well I hope its not the systema gearbox, I just got mine in the mail today... lol

Ahhh well it's a possibility, I'm not going to risk opening my new mechbox myself, I'll let someone more knowledgeable do it.

seriously, bring it to a gun doc, all problems solved

I was planning on it, I just like making sure I've done everything possible myself first.