Periodic burst fire o_0

[kalnaren]

Quick question,

Noticed at the last game, every now and then, my MP5 would fire a 2 or 3 round burst in semi-auto. 9 out of 10 semi-auto works fine.. but every now and then it fires off a burst. Strange thing is that it's not like it's stuck on full auto -I can hold the trigger down and it will only do a burst before going back to normal semi-auto. Not sure where to start looking for the cause of this. I figure it might be something with the selector plate/cutoff lever or some such but getting into that stuff is a bit beyond my knowledge of troubleshooting AEGs.

Any pointers on where to look would be appreciated

[Styrak]

Yup you're right on track. Probably has to do with the selector plate or cutoff lever.

[Crunchmeister]

I started experiencing a similar issue with my JG MP5. Full auto works fine, but when I switch to semi, I may get a single shot (most of the time), or a burst. I suspect it's the cutoff lever in my mechbox causing the problem, but haven't opened it to confirm it.

I personally don't have an issue with this, as I rarely use semi and shoot short bursts in auto. But it sounds like you're experiencing the same problem I am.

[m102404]

Most likely the cut-off lever/switch block (the upper part that gets push in to make contact and flicked out by the cut-off lever),not interfacing/working right.

Over/under shimming or over-tightening the screw that holds the lever to the mechbox shell can also bind the lever a bit so that it "sticks" now and then.

Best of luck!

[kalnaren]

Originally Posted by m102404

Most likely the cut-off lever/switch block (the upper part that gets push in to make contact and flicked out by the cut-off lever),not interfacing/working right.

Over/under shimming or over-tightening the screw that holds the lever to the mechbox shell can also bind the lever a bit so that it "sticks" now and then.

Best of luck!

That sounds like something I can look into!

I aquired this gun in trade and was informed the MB is stock TM, not sure if it's been opened or not. I should probably check anyway and give it some TLC since it's an older mechbox.

[kalnaren]

Originally Posted by m102404

If you can make it reliably shoot a 3rd burst on Semi...just mark in additional red bullets on the trades and keep it as is! LOL

haha, the thought had crossed my mind.

[Marriott]

Its not actually a fault issue really. With the mechanism for semi auto fire, you pull the trigger and a contact pin moves forward bridging 2 contacts to make the circuit. On a full trigger pull this engages then the piston gear pulls the return leaver to reset the switch... Now you can simulate burst fire on semi auto easily. Pull hte trigger slowly, the trigger mechanism moves forward slowly creating an arc that bridges the contact and the duration of this slighy trigger pull allows a burst.

The reason i think this is the issue is that you stated that it only happens in semi auto mode and that it rarely happens. You also mentioned that upon the full pull it returns back to semi. This is too consistant or inconsistant for it to be sticking. Sticking would start to increase its occurance.

Try the slow trigger pull to simulate what i am talking about. The problem with this is you really need a Mosfet or Trigger maser to offload the amps/current going to the switch creating the arc. Repeated arc'ing carbons up the switch and can damage it/weld it on to full auto. The mosfet/trigger masters usually bypass this allowing only 100mah to the switch = no arc's

Hope this helps

[m102404]

Originally Posted by kalnaren

....Strange thing is that it's not like it's stuck on full auto -I can hold the trigger down and it will only do a burst before going back to normal semi-auto. ....

While it's true that a slow squeeze can do weird things...this is what I was going on for my guess.

[Crunchmeister]

I just tested this with mine and it makes no difference if I pull the trigger slow and gently or fast and all the way. I get random bursts in semi.

[m102404]

that's a where there's something amiss with the cutoff/switch (NOTE: Without seeing it, this is all guessing and just based on past experience)....

In a rare occurrence it would be the selector plate moving too far back and holding the cutoff lever just slightly on full before "jiggling" back to position. But if this were the case, it would happen right off the bat...not progressively happen after the rifle was working fine.

Techobo's M4 had this issue with a KA replacement selector plate, he took 1mm off of the notch to correct it, otherwise it would mostly fire full auto (but his never went back to semi at any rate).

[jtf2-phalanx]

Originally Posted by Crunchmeister

I just tested this with mine and it makes no difference if I pull the trigger slow and gently or fast and all the way. I get random bursts in semi.

Yup, I had the exact same problem in my M4 and it was the cutoff lever.

[Dusti69]

ive experienced something like this in at least one of my aeg's but im not sure which it was.
i wanna say my jg dragon/ika zuchi but im not sure.
i was probly shooting it too fast in semi and it randomly took off and fired a good burst as if i had it on full auto. its only ever happened a few times

[maporms]

Cut Off lever is the most probable issue here. Had the same problem with my AK Beta Spetsnaz, had the cutoff lever removed. Problem is i lost my semi-auto mode, but hey, I don't use semi during games not unless I'm doing sniper duties.