Trigger won't work

[Brother Buckwheat]

I just got started building AR's, looked like fun and I'm pretty much a tinkerer.
I'm on my 4th Polymer 80 build. Lowers 1,2 and 4 the trigger works properly. lower 3 doesn't. All milling is within spec. I've switched trigger groups between all 4 and build #3 the trigger will still not fire.
I'm trying to figure the terminology to explain what is happening, but to explain best I can- hammer is down (fired), I hold trigger back, put hammer to fire position, release pressure on trigger, the piece that resets the sear? does not come back far enough to reset trigger to fire again.
Has anyone got any idea what could be going on?

 

[Rickjames80]

Following, I had a couple issues with my first AR last weekend. I had to go to safety on a couple rounds so the trigger would reset

 

[Buck Fever]

Is your disconector spring in properly?

With an 80% I like to use a drop in style trigger assembly like a Rise or Chip McCormick, something that holds everything together. That let's the pin holes in your receiver be a bit off without having much effect on the trigger.

 

[Brother Buckwheat]

Is your disconector spring in properly?

With an 80% I like to use a drop in style trigger assembly like a Rise or Chip McCormick, something that holds everything together. That let's the pin holes in your receiver be a bit off without having much effect on the trigger.

My disconnector spring is in, correctly, on all 4 receivers. I can swap trigger parts among all 4. Receiver # 3 no Bueno on sear engagement on release of trigger. I have mic'ed #3 and it is within +/- .006 of all the others. Dunno, odd to me, Just hated to waste the $$$$ and have it worthless.
I'll pick up a drop in for that receiver and give it a try. Thank you for the suggestion.

 

[Farmerboy78]

That .006" may be all it takes to not be functional.

 

[dfanonymous]

It's the hole where the trigger pops out by the trigger guard more than likely is not milled out all the way/right, or you are off where you trigger pin holes where drilled slightly. This can be for any number of reasons. The jigs are just there, and it's under the assumption that all tolerances are equal. The amount of pressure used to clamp the jigs together is enough to cause a tolerance issue.

 

[cohunt]

Single piece drop in I bet will fix it, if the hammer or trigger pin are not completely straight it will cause binding of the sear-- had it in one of mine

 

[sea2summit]

Have you check the specs on the holes on each side of the receiver? I've got a poly lower (.22) that likes to walk pins and the first symptom that tells me a pin is out of alignment is what you described.