This is my first build so that probably has something to do with this.  I got my DPMS lower all put together with a DPMS LPK, MIAD grip and CAA stock matched up with a 16" Rock River upper.
Today I took it to the range to make sure everything functions properly.  Got through about 10 rounds on the first mag then the trigger didnt go back into battery.  It doesn't happen everytime but probably about 70% of the time.  I either have to push the trigger forward or snap it back into position.  Did I do something wrong?

Check the disconnector spring and also if the hammer/trigger spring was installed in the right direction.

Step By Step Instructions Here

Take the upper off the lower and perform a function check without ammo.
An improperly installed disconnector can result in full auto slam firing.

As stated above, make sure you have the proper spring installed under the disconnector, in the proper orientation.
The wide side goes down.  Make sure you did not confuse this spring and the bolt catch spring.
Make sure the trigger and hammer springs are installed correctly.  It's easy to get the hammer spring installed upside down.

During these test do not allow the hammer to hit the lower receiver, put your free (left) hand in front of the hammer to prevent it.
Without touching the trigger, cock the hammer back until it catches on the sear.
Engage the safety.
Pull on the trigger - the hammer should not drop.
Disengage the safety.
Recock the hammer, guard it from hitting the receiver.
Pull the trigger - hammer should fall
Without releasing pressure on the trigger, recock the hammer.
The disconnector should catch the hammer.
Guard the hammer and release the reward pressure on the trigger.
The hammer should move forward slightly and then be caught by the trigger sear.

Try this a couple of times.  
If this does not work, tell us which step is failing the check.

If it passes then we can start looking in the upper for a reason.


Function Check

When hand testing this it didnt re-set twice like what was happening on the range

A very loose thought, what if a ran a file along the hammer/disconector engagement point? Just seems like it gets hung up the smallest amount.  Bad idea?

Are you saying the hammer is captured by the disconnector and when you release the trigger the hammer and disconnector ride forward together and never separate, so the hammer sear never engages the trigger sear?





Not a good idea to alter the sear surfaces unless you know what you are doing.
Unless there is some obvious flash or a burr.

Are you saying the hammer is captured by the disconnector and when you release the trigger the hammer and disconnector ride forward together and never separate, so the hammer sear never engages the trigger sear?



Yes it doesnt disengage the disconnector until I push the trigger forward.

The trigger doesn't return forward under spring pressure?
That sounds like the trigger spring is installed incorrectly.

I guess Ill take it back apart

The square part of the trigger spring sits right behind the hammer and the feet point towards the magwell, does that sound right?

The square part sits UNDER the trigger and the legs wrap forward from the back counter clockwise.
Look at the second pic on the left.


Look closely at the trigger bottom right.

Well hell sounds like that could make a difference.  Thanks for your help

There was no spring force pushing the trigger up and back to the ready position.  Recoil was probably bumping things around enough to get it to fire some times.

Let us know how it turns out.  

Well in and out im done switching it, might find some time tomorrow to test it. Thanks again

I am new to building also.
In the pics of all the parts is that the way the hammer spring is supposed to be installed?

Yes.  
The legs wrap counter clockwise and emerger from th ebottom of the hammer, if you look at the left side of the hammer.
If you install it upside down, the feet do not provide enough down force sothe trigger pin will walk out of the hole and you may have spotty ignition due to lower hammer force impacting the primer.

That pic has saved me from pulling my hair out on more than one occasion.  

Yes, but when you install it, you need to bend the legs so that they point towards the front of the lower.  The legs will be on top of the trigger pin.

??  
The only way for the legs of the spring to reach the trigger pin is to point to the rear of the lower as depicted in the picture above.
You essentially lay the legs of the spring on top of the trigger pin, then push down on the hammer against the spring pressure and install the hammer pin.

Here I assume we all agree the "front" of the lower is the end closest to the muzzle.  



ETA:
I think we agree and are just saying it differently.  
You need to rotate the cross piece of the hammer spring so it bears against the back side of the hammer.
The legs will initially point forward.
Then you place the legs of the spring on top of the trigger pin.
Then you push forward to install the hamemr pin.

In that parts list is the Dissconnector facing backwards?
(I have not recieved or installed my LPK yet)

Yes, look at the assem. photo above it . It shows proper placement of disconnect & trigger .

you sir are correct, put the legs on the trigger pin then push down, Im not sure why i said they should point to the front.  Thats basically impossible

Why didn't you function check the lower, before you took it to the range?

Well I thought I did. Obviously I wasn't looking for the right things that could be wrong.  We are all new to a new firearms system at some point.  Next time I will heed your advice, thank you.

I'm not trying to be a smart ass. Sorry if I come across that way. I was lucky enough to have bought a complete rifle before I built one. I had something to look at, and compare with, as I assembled my first lower.

The function check was something I had to perform three times before I even understood what it was that I was supposed to be checking.

No problem, luckily I have this place and people with enough knowledge to tell me whats wrong without ever seeing said problem.