First bb fires fine, second just 'pukes'??

[Phreakish]

I've toyed with, upgraded, and torn down so many AEG boxes its not funny, I know how things work inside them and have no issues with any of the guns I've upgraded, unless I use crappy parts...

I recently picked up a very modified G&G M14 from a board member, The gun is AWESOME, fires like a bat outta hell, hits hard enough to sting through my opponents tac vests at range, and is accurate as all get-out...

BUT, on single-fire mode, the first shot will go perfect, leaves the barrel nice and straight, high velocity and hits dead-center in the scope.  The next shot will sound completely different, and leave at a much lower velocity and fall VERY short - this sucks when shooting from a concealed position at a target I've been waiting for, and give up my position and get owned...

The gun does NOT do this on full auto, it fires a big laser of bb's straight and true.  Only on semi does it do this, and about every 5th shot will come out at warp speed and be over-hopped because of it and climb like a homesick angel...

I dont fault the guy I bought it from, its probably my own fault as the first night I got the gun I had no idea about the spring decompression and a friend fired the gun with the bolt locked back (and also in single fire mode) which allowed it to be fired with a non-operative anti-rev latch, which took out the first tooth on the piston - I replaced it with a reinforced CA piston (for now, this is temporary).

Any ideas what may cause this? the GB seemed lubed well, but the piston rails weren't that smooth, I reused the upgraded piston head that was in there also.

[warlock]

If the AEG gears are not timed correctly during re-assembly, this can and will happen. Basically what is happening is every so often you'll catch the anti-reversal and leave the piston half-cocked (take the gearbox out, attach pistol grip, insert motor, hook up battery, fire a few rounds) and that can cause wierd things to happen when it goes to cycle that round.

Pic of correct timing:

[Phreakish]

timing? I've read EVERYWHERE that timing is a myth, and by looking at how a GB  works inside, it IS.  So long as everything is placed correctly, or close, to how it would be in the 'just fired' mode, it'll operate flawlessly.

Also, the G&G M14 box works like a PSG1, in where the piston is compressed at the end of each cycle, so the trigger pull immediately releases the piston, instead of having to go thru a whole cycle.

[Vince]

The high speed motor and high speed gears coupled with a high voltage battery could be the culprit. If you are firing in semi really fast, you could be short stroking the piston, perhaps. It's fast enough to, with quick enough trigger input, I think. I dunno, though. Glad to hear that other than that everything is cool.

[Phreakish]

yeah, the gun rocks Vince! thanks!

I'm thinking that thats what is happening, the high ROF stuff is short-stroking things, even w/o fast trigger input.  If I hold the trigger back the whole time, or just tap it, even with several seconds between shots, it does it.  I'm thinking I'll have to drop down another cell to a 7cell battery and try that for semi-only.  But with the 8C and full auto, its wicked...

Or I can always put a stronger spring in and see what happens, haha - but then I'm sure it would be too hot for AA games when/if I'm able to play with ya'll.

[Dust2Dust]

Timing is a myth.  After each cycle, it resets, so you'd only know if it was timed incorrectly during the closing of the gearbox, because the tappet plate would sit funny and it wouldn't close; and if you did have it closed, your piston would lock back and not cycle.

The M14 has a spring release, so even if it was "timed" incorrectly, you'd let it fly forward, and everything would be fine.  

Vince's suggestion makes the most sense.  Try dropping the battery down to the next level.  If that doesn't work, maybe give the guys over at AEX a call or email G&G directly.  Both will help you out.  G&G has a huge section of FAQ's with the M14 on their english page, if it's already been covered there, maybe there is an answer.
www.guay2.com

[Phreakish]

out of frustration, I took the GB back out of the rifle last night, and with the reciever removed from it you can actually watch the piston/spring operate.  It seems to be stroking completely on each shot in semi, I wonder if the nozzle is hanging on something, or something else is jamming up.  I might try lubing a small batch of bbs better and trying that... Could also be the mag, but I'm not sure.  Full auto still turns the bb's into dust if I fire against something hard, so its firing perfect in full auto - just wish I could trust every single-shot was gonna fly right...

[Phreakish]

my new set of bearings has arrived today, so I'll have the GB open again.  I lubed things with a bit of silicone spray and its now about 1 in 4 that drops short, but after 10-15 shots it seems to start doing every-other again...  Also tried a 7 cell, too much lag between shots on semi, and a struggling noise when firing full auto, but it didn't help the puking...  Hopefully once I'm inside again I can figure out the issue, its drivin me nuts as its brutal to let loose on someone at close-ish range on full auto, I like to kill my opponents but not by busting up their arms and hands, haha.

[-MAD- SARGE]

Could the piston head be bad or the o-ring?  Dont know, just thinking. If on semi the o-ring is not getting a good seal on the compression stroke, velocity would drop. Maybe with semi it is enough to allow the piston head to beak the air seal on the return and then not seal properly on the compression.  And maybe in full auto, it is enough to slam the piston head to seal for compression. I don't know?  This is indeed an odd problem. Your airnozzel is set properly as well?  

You may know this already but when you take out the cylinder, piston, and cylinder head try this. Try putting the the cylinder head on the cylinder and then with your hands push the pistion with pistion head through the cylinder back and forth while blocking the air discharge hole on the cylinder head. When you push in on the piston, you should have a good seal and thus good resistance. And then when you pull back on the piston the seal should break and be easy to slide backwards.

If when you are pushing the piston forward with the cylinder head discharge port covered up, and you do not feel resistance or it is very poor. You have a seal problem and may need a new o-ring or piston head.  Usually it is the o-ring.   I would think that a bad seal would be most noticable on semi auto than full auto. I could be wrong though to your problem, Im just giving out an idea.

[Phreakish]

I'll have to try that.

I opened up the box at about 4 pm today to put in the bearings, and grease it all up for tomarrow.  Well, its been 3 hours and so far all I've gotten is crap.

The bb's just lob out the barrel, double-triple feeding and NO velocity to speak of.  I have no idea why this is happening now, everything worked okay yesterday, still had the same semi-auto problem but at least it was usable, now its like an LPEG but worse... I get great air from the nozzle, very hard shooting and with the piston/cylinder out it has good enough compression - there is a slight leak but nothing that the piston shouldn't seal up when being slammed home... It must be something with the hop or the nozzle to hop seal, ARGH.

When firing upside down and a couple bbs in the hop, it wont blow the extras out, so there must be a decent enough seal there.  I did notice that there is a small ring on the very aft most part of the hop (its like an AUG hop) that seats into the front of the mechbox, its got a slight crack, but this part shouldn't have anything to do with a seal... This is very frustrating, any info would be much appreciated.

[Phreakish]

tried a new cylinder and cylinder head that I have here, no luck - still the same prob.  I tried a spare O ring, no luck...

I'm at a loss here, there must be a MAJOR problem if its firing like this, the teeth on the bottom of the piston are a bit worn, but nothing abnormal, I guess I could try another piston, I'd have to repair the initial tooth, but if it at least works for a couple shots I'll know whats broke

[Dust2Dust]

Try your best to isolate the problem.  Just to be sure though, look over every single part in your gearbox, and that is related to the firing process, ie barrel, hopup, etc...

This is a really off the wall problem.  Contact ASGI and see if they have any ideas.

[Phreakish]

I'll be doing that.  Looks like I'll be running my 16 tomarrow...

I cleaned ALL the grease out of the system, I was using some 'experimental' stuff, and I think it was causing problems.  I only ran a few test bursts w/o the grease (no grease on the piston/cylinder/head/hop/barrel, etc, but the gears are well lubed).

It seems MUCH better now, but its still not anywhere close to what it was just hours before I started.

I'll try to get some grease while I'm down in phx, and maybe a few other parts too to try out.  Only things I can attribute it to is the cylinder/piston or the o-rings on the cyl head maybe.  I'll get a bunch of new orings and grease and try things out later... I'm stumped as of now tho.

[azsarge]

Moved to Troubleshooting, where it belongs.

[Phreakish]

ah, thanks, sorry for putting it in the wrong place - was frustrated/confused

Anyway, I got some new (better) o-ring lube from JT yesterday after some games with some of ya'll (great games BTW, thanks!).  

I just got done going through it all again, and its working MUCH better - some of the bb's still dont fire quite right, but its very close to where it was before.  Turns out that the piston head in the gun is a silent head from ASGI (go figure) and at least one of the holes in the face of the piston was clogged from the factory, and the whole setup is very sensative to the amount of grease used on the o-ring, too much or too little and it wont work right - there was also a bit of debris in the oring groove - I guess because this system has such a high ROF it was sucking back the bb's - as I had a hard time pulling the piston backwards in the cylinder when I had it all removed... Now I just gotta figure out why it wont fire semi auto