Firing FA in semi - Armalite

[GuzziHero]

I have a bitsa Armalite that is firing in auto when i squeeze the trigger in semi. Im suspecting that, heaven knows how, the trigger contacts have closed up.

 

Ive inspected them, they are not burnt out or worn.

 

Any other possible suggestions to try other than spreading the contacts would be welcome.

 

Thanks!

[RSM]

Worn/Iffy cut off lever, or the spring/tappet mount for the spring that pushes on the cut off is gone/weak

[GuzziHero]

The spring seems to return it ok when messing with the selector plate...

 

Ill look at the SAC lever next. Thanks!

[Docv400]

It won't be anything to do with the trigger contact strips.

As RSM suggested, it'll be some fault with the cut-off mechanism.

Where he said 'tappet', I think he meant 'selector plate'.

The cut-off lever may be worn down where the cam bears on it (not common on the version 2 gearboxes though).

The lug that lifts the trigger contact block could be broken/damaged.

[GuzziHero]

Right, Ill investigate further tomorrow.

 

Much appreciated, chaps!

[Docv400]

Take some pictures of the insides when/if you have to strip it down again.

[infected]

Yep. I bet cut off lever most likely. Possibly a tappet issue.

[Cosmitz]

Atm i have a similar, yet amusing issue. After 'somehow' loosing the contact plate on my selector plate, i replaced it with another plate from a old selector i had around the house. I also replaced a broken lever, which caused me to not have semi, with a fully functioning one.

 

The issue i'm having now is that, somehow, when i commute to either semi or auto, my gun keep firing until i commute it back to safe. In some positions sometimes it's ok more or less but it's definitely not skirmish-ready. I'm gonna open her up again today to see wth is going on, and i have a spare triggergroup in case. And no, the blades are not getting stuck.

[Almighty]

I have a bitsa Armalite that is firing in auto when i squeeze the trigger in semi. Im suspecting that, heaven knows how, the trigger contacts have closed up.

 

Any other possible suggestions to try other than spreading the contacts would be welcome.

 

Have you tried pulling the trigger all the way back when shooting semi? You have to be a little more deliberate about the pull.

 

If you pull very lightly or "feather" the trigger, the slider moves just forward enough to make contact and start the AEG firing.. but not quite forward enough for the cutoff lever to disengage.. so the gun would keep cycling.

[Docv400]

Yep. I bet cut off lever most likely. Possibly a tappet issue.

The tappet plate has no affect on the electrical circuit or the firing of an AEG, it's there solely to move the nozzle back and forth.

You could leave it out of the gearbox and it would still cycle in semi and auto.

 

[GuzziHero]

Update! No pics cos I have no camera batteries.

 

Changed the cut off. Out of the gun, the gearbox works normally.

 

Assemble the gun, problem returns.

 

Heyulp!

[Abelius]

Does the mechbox sit flush in the body? Have you had to replace it lately?

 

I get every now and then gearboxes that sit crooked in the body without modification, causing the selector switch to engage the selector plate a bit further than it normally would. Usually this causes lack of safety though, not FA on semi...

[GuzziHero]

It seems to drop in OK. Far as I know it hasnt taken any knocks.

 

Odd thing is, this started on a very cold evening game and my CA XM177E2 started the same thing at the same time.

 

This particular gun is a custom, but the bones of it are a JG gearbox in a CA body. Its always worked fine before. It runs a 9.6v Crane battery, a G&P M120 motor and has an insane ROF.

[infected]

It could be over spin causing it, although doubtful unless the spring that forces the gun to function in SEMI is missing or weak. Check to make sure the spring that goes between your cut off lever and selector plate is in place and staying there when the gearbox is slide into the gun.

[GuzziHero]

I shall investigate tomorrow (today?!)

[Stealthbomber]

I think all the people who're saying "tappet" actually mean "cam".

 

One simple tip:-

Try shooting the gun with a low-powered/almost flat or low voltage battery.

Because everything's moving slower it gives the cut-off lever a better chance of working.

I've found that running a gun on an 11.1v LiPo will often cause it to fire only in auto but returning it to a more sensible battery will allow it to operate correctly.

 

 

If it's not the cut-off lever (which it almost certainly is), take a look at how the trigger interacts with the back of the moving trigger-contact block.

 

The cut off lever is supposed to lift the contact block and allow it to ride over the top of the trigger and slide backwards.

If there is a particularly sharp edge on the top of the trigger, or burrs on the contact block, they can wedge together so that the contact block doesn''t slide back as it should.

 

You can improve this by smoothing and rounding (with emery paper or a small file) the top front corner of the trigger, where it pushes on the contact block and also doing the same to the bottom rear edge of the contact block.

Be warned that if you OVER-do this the trigger won't be able to push the contact block forwards and you'll kill the gun.

Doing this correctly can make the gun shoot noticeably crisper in semi though.

 

Here's a pic to demonstrate the idea:-

 

Note that this pic relates to a G&G L85 but you can see the principle...

The grey part is the top end of the trigger which pushes the contact block forward.

If you can reduce the area of contact between the trigger and the contact block it'll make it easier for the cut-off lever to flip the contact block upwards so it can spring back over the top of the trigger.

[GuzziHero]

Thats definitely worth a look at, cheers

 

So when the block slips off the trigger, the block lifts slightly... and doing that will make the block slip off more smoothly and slightly earlier while still making sure it goes forwards enough to engage the contacts. Thats what Im reading here, and it makes sense. So after one shot is fired, the block returns and cuts the power hence making it semi auto.

 

Deviously clever design!

 

Thanks Stealth!

[Stealthbomber]

Thats definitely worth a look at, cheers

 

So when the block slips off the trigger, the block lifts slightly... and doing that will make the block slip off more smoothly and slightly earlier while still making sure it goes forwards enough to engage the contacts. Thats what Im reading here, and it makes sense. So after one shot is fired, the block returns and cuts the power hence making it semi auto.

 

I think you've got it.

 

The contact block is spring-loaded so it wants to pull back, away from the contacts, right?

The cut-off lever hooks under the contact block.

When you pull the trigger the top end of the trigger pushes the contact block forward, bridges the contacts and the gun shoots.

After one shot the cut-off lever jerks the contact block up so it can ride over the top of the trigger and retract, thus stopping the gun from firing.

 

Anything you can do to make this smoother will help the gun stop firing after one shot in semi.

 

I'll say it again though: If you over-do any mod's you'll find that the contact block will retract BEFORE the gun can fire and you will, basically, have buggered up the gun.

 

It's worth looking at this with the gun in bits.

Hold the trigger pivot in place with one finger and then pull the trigger.

Now, (if you can) try poking the contact block upwards with a pick or screwdriver.

It should only take a couple of mm of movement to trip the contact block so it retracts.

Any more than that and there's room for twiddling.

 

In practice, simply filing any rough seams off the trigger and just smoothing off the contact block will be enough to result in a noticeably smoother cut-off after semi shots.

 

Course, you'll drive yourself potty trying to look at this on a V3 gearbox cos the trigger mechanism is so bloody fiddly.

Only really viable with the V2 or any gearbox with a straightforward method of actuating the contact block.

 

*EDIT*

Just occured to me...

Before anything else, check that the contact block IS able to move smoothly.

I bought an Element trigger block and the contact block was so bloody tight inside it that it never had a chance of sliding backward and forward at all.

[GuzziHero]

Will do that. I didnt get chance as I wanted to...Ill get round to it and report back

[shinobi_uk]

Will do that. I didnt get chance as I wanted to...Ill get round to it and report back

 

This is a problem i've had a lot of experience with recently.

 

I've been playing with 2 M4 mechboxes and had ALL of the above symptoms and found them to be related to both the cut off lever AND the electrical contacts at the lower of the switch assembly:

 

The issue of the gun cycling on FA when you move the selector I found was down to contacts behind the selector plate clipping the gearbox shell, I pushed them in a little and this solved the problem, but pushing them in too much resulted in the gun not firing at all on semi so it's a case of trying and testing (which is a balls ache as you must put the lower reciever on each time).

 

The problem of the gun firing FA whilst in semi was due to the cut off leaver, it wasn't broken but it had worn down just enough to no longer be fulling effective, I swapped it out for a new one and the problem was fixed instantly.

[GuzziHero]

Sorry for the necro but... I fixed it.

 

What happened was, for some reason the semi latch was VERY sloppy, so it wasnt lifting enough. I fitted a sector gear from a DE M4 and that has a longer cam, so it now activates correctly.

 

I have no idea why this suddenly happened, but the issue is sorted

[Stealthbomber]

Great stuff.

 

Funny, when you look at this stuff in detail you start to realise that the trigger system really DOES rely on some fairly tiny movements to make it work.

 

Makes you wonder why they didn't invent it with a lug on the left side of the sector gear to operate the cut-off lever in the same way you have one to operate the tappet plate on the right-hand side.

[GuzziHero]

Hmm...you have an idea there. What if someone used that to make a dual-sided selector?

 

That DE is awfully incompatible with other guns. The gearbox is shaped differently at the back, the trigger switch is a different shape. Mag release pin thinner than normal etc etc.

 

Even the semi-cut off latch is a different shape, it doesnt arc up anywhere near as much as the 'standard' type...and its that difference that made its sector gear work for this gun. I tried 3 'standard' sector gears and no go on any of them.

 

Oh, another gun I have, an XM177E2, started with the same problem at about the same time. Then the grip broke off when a friend accidentally dropped it. I just fitted a new grip and disco, it starts working just fine again. Answers on a postcard...