On a 80% build, easy enough to break the problems down to a few areas to see what is out of spec.


So the first thing we do is install the hammer and trigger with springs, without the disco all together.  
This allows us to cock the hammer back to make sure that trigger sear is retaining the hammer correctly,
That when the selector is set to safe and the trigger pulled, the hammer is not released from the trigger,
When the selector is set to fire and the the trigger pulled, that the hammer can travel all the way forward without binding on the trigger sear.


Now with the disco now installed, We can take it through its checks.
So trigger untouched, cock the hammer past the disco, and make sure that the free gap between the disco and hammer rear sear a they pass by each other is only .001" to .003".
Next pull the trigger all the way back, and over cock the hammer to the disco sear, and with a slow trigger release, make sure that the disco is releasing the hammer to being with, and when the disco releases the hammer, that the trigger front sear catches the hammer.


So if you do the above check and tell use which one of the above is the problem, then should be a easy fix.

ram1998,  if the free gap is too large/advanced, then the disco will release the hammer before the front of the trigger is in the correct position to catch the hammer reliable each time.  Hence the disco should not let the hammer go until the trigger is dam near all the way back to it forward free rest postion.

The gap is easy to reset, via removing some metal from the front/bottom of the disco where it seats against the top/front of the trigger.   Take your time with removing metal with a couple of dry fitting, until you get the free gap to .001" to .003" (about that of a sheet of paper).

https://www.ar15.com/archive/topic.html?b=3&f=66&t=647630

Not sure if its a members only thing, but check in your profile to see if you can turn on notifications.

Not really, and if all the parts are in spec, including the lower receiver pin channels, then the Free gap should be .001" to .003".

Now with 80% receivers that the pin channels may be off when drilled, and crapamatic cheap FCG  parts to boot, God only knows what you end up, and most of the time have to time the parts correctly instead (including the free gap).

Been a mod for so long (over a decade) that I even forget what the non members profile page looks like.

But click on your name up on the left top of the page once you are logged on, click on  changer prefences on the bottom left, and see if you have a line a few items down on the right that is labled "Subscription Default"  If you do, then change it to receiver email when something is posted in one of your subscription (any topic you start, or one that you have posted in).

Wrong forum to be posting this type of advice in, and would be better advice for the parts swapping only "build it yourself" forum instead.

Hence in this forum, the sound advice given here it how to bring the entire rifle together together as a working/functioning rifle; be it smith'g the parts, including the FCG if needed as well.

Hence the AR-15 with the mass suppliers of parts (some that are total shite), does not often turn out to be as "plug and play" as one would wish, and when you are working with a completed 80% completed receiver, the chances of "plug and play" with parts (even if totaly in spec) in such a receiver a even less of a chance of plug and play as well.

Again, we know that the problem is either the disco is out of time, or the lower receiver is not milled correctly.

The disco is easy to re-time if needed, and as for the if the problem is the lower receiver, don't see the opt wanting to have to throw it away and start again on a new receiver, so smith'g the needed FCG parts to bring all of it into a working rifle is not hard to do.

As for the companies that you names, trust me-they are tweaking/cleaning up FCG parts during their factory builds to get the rifle functioning as well.