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I'm aiming this mainly at those lucky amongst us to have significant experience with full-bore semi-auto AR-15's. Those with .22 or 12b semi's may also have useful info.

The issue trying to be diagnosed is a malfunctioning gun that is either double firing or the hammer is following the bolt group home resulting in a 'dead' trigger.

The usual suspects have been eliminated;

- Bent trigger/hammer pins
- Enlarged/elongated receiver pin holes
- Worn/overly polished sear/disconnector/trigger shelf
- Weak/damaged hammer/trigger springs

The only other thing that seems to be left is a weak disconnector spring. Does anyone KNOW if a weak/damaged disconnector spring could lead to the above problem or have documented accounts of any other common things other than the list above which can lead to it?

Any assistance would be greatly appreciated.

What trigger is it?
Could be set up wrong or, as you suggest, weak or worn spring/disconnector.
Cheap to replace or adjust the spring in the first instance to eliminate that.

If it is dirty or has foreign bodies in the trigger area it could be stopping the disconnector from (fully) engaging.

I had this when I accidentally put the disconnector spring in the wrong way up and it doubled.

CDM5 wrote:I had this when I accidentally put the disconnector spring in the wrong way up and it doubled.

This is supposedly a fairly common cause of this problem.

The other common problem that apparently causes this is an out-of-spec receiver, where the trigger pin holes are not correctly placed or out of round.

Mattnall wrote:What trigger is it?
Could be set up wrong or, as you suggest, weak or worn spring/disconnector.
Cheap to replace or adjust the spring in the first instance to eliminate that.

If it is dirty or has foreign bodies in the trigger area it could be stopping the disconnector from (fully) engaging.

That's the problem, I don't know! It came as part of a 'deal' on a Firebird Precision lower receiver (TAC-99). It was initially installed about 2 years ago and has ran flawlessly until now so I'm guessing something is fatigued. There was a bit of crap in the mechanism, including where the hammer connects with the trigger and underneath the back of the trigger part of the FCG;

https://www.flickr.com/photos/156521976 ... 4051183384

Unlike a 'proper' AR disconnector spring it doesn't have a fat and skinny end, rather the one that came with the FCG has a extra coil bend upward to grip the back of the disconnector to keep it in place/orientate it.

I have now replaced the disconnector spring with one from a spare FCG for the original BR99 (also cylindrical, not fat/skinny ended) and will hopefully get to test it tonight. Need to get it sorted before mid August as I don't want a repeat performance of this ;

Your flicker picture comes up as "Unauthorized Access".

Does this work;

https://www.flickr.com/gp/156521976@N05/cS4RtZ

Or this;

https://www.flickr.com/photos/156521976 ... 4/sizes/l/



https://farm5.staticflickr.com/4329/361 ... 28_z_d.jpg

Those links all work fine thanks.

I don't like that spring tail coming round the disconnector. That could be the problems right there but without seeing it in the flesh it'd be difficult to tell.

Mattnall wrote:Those links all work fine thanks.

I don't like that spring tail coming round the disconnector. That could be the problems right there but without seeing it in the flesh it'd be difficult to tell.

When I first saw that I thought the spring had uncoiled and jumped over the disconnector but on closer inspection realised that it was designed that way

I took it to the clays with me last night for a test firing and it cycled two magazines without doing anything silly, so replacing the disconnector spring and cleaning the gunk out the FCG has done the trick. I've got a practice PSG match before my next big comp so hopefully if that wasn't the fix I needed it'll show itself there. I think i'll still take a spare gun to the big comp though, just in case.

Unbelievable that a spring half the size of something you find in a clicky ball point pen can cause so much trouble!

EDIT: IN cleaning the crap off the FCG I stripped it of the grease that had been originally applied - any ideas what to replace it with?

Blackstuff wrote:

Mattnall wrote:Those links all work fine thanks.

I don't like that spring tail coming round the disconnector. That could be the problems right there but without seeing it in the flesh it'd be difficult to tell.

When I first saw that I thought the spring had uncoiled and jumped over the disconnector but on closer inspection realised that it was designed that way

I took it to the clays with me last night for a test firing and it cycled two magazines without doing anything silly, so replacing the disconnector spring and cleaning the gunk out the FCG has done the trick. I've got a practice PSG match before my next big comp so hopefully if that wasn't the fix I needed it'll show itself there. I think i'll still take a spare gun to the big comp though, just in case.

Unbelievable that a spring half the size of something you find in a clicky ball point pen can cause so much trouble!

EDIT: IN cleaning the crap off the FCG I stripped it of the grease that had been originally applied - any ideas what to replace it with?

TW25b grease would be my choice.