Ok, got to the range this morning with my new, and first ever build.  The trigger is a bit confusing.
 

Running dummy rounds through, fed from the mag it feels decent, gritty but not that heavy.  Live rounds are a different story.  The first round chambered from a mag the trigger gets VERY heavy, at least twice as heavy as with the dummy rounds.  Any round chambered from the mag after that is the exact opposite.  The pull drops back down, the reset is short and the take up is almost non-existant.  Grittiness is still there, but I can even see the machine marks on the contact surfaces, I can polish that out.  But I have no idea why theres such a difference between the first round fed and all the others.

 

That is a very odd problem you are describing. Can you give us some specs on your build? Specifically what LPK, BCG (FA?), lower/upper.

 

Since you built it yourself, let's just check the basics and see if anything is off. Check the disconnector spring for proper orientation, wider part down in the trigger housing. Sometimes that gets mixed up with the bolt release plunger spring. Also check the trigger/hammer spring orientation.

 

 

Also, this test is pretty good to see if anything funky is going on with your selector:

 

SELECTOR TEST

 

For this test, you will only need the lower receiver group. Prior to performing the test, ensure that all parts and springs are properly installed.

 

1. De-cock the weapon and place the selector in the FIRE position.

2. Pull the trigger and hold it tightly to the rear until the next two steps are completed.

3. Force the hammer back onto the disconnector.

4. Rotate the selector to the SAFE position.

 

PASS: Hammer resets on the trigger.

FAIL: Hammer falls to the fired position.

 

If your weapon fails the selector test, replace the following parts (with known good ones) in order and repeat the test after each part is changed.

 

1. Disconnector Spring

2. Disconnector

3. Hammer

4. Trigger

along with the above tests, make sure the disconnector spring was installed correctly. (fat end down)

PSA premium lower build kit. The basic single stage trigger. I've torn it down and it is assembled properly. I don't know if it's a binding with the hammer and bcg putting a strain on the trigger group or what.

 

FWIW I love the pull on the second and subsequent rounds. It's great for long distance

When you rack the bolt are you letting it go from full open?

I've been using the bolt release most of the time. Occasionally the charging handle, when I use the CH I'm pulling it back all the way before letting go

It's just the trigger pull. It fed and fired fine.

Take a picture of your trigger group from above if you can and post it. 

Did the selector test pass with flying colors? What are the specs on the rest of the items? BCG (FA?), lower/upper...

 

Other than an out of spec trigger group or lower, something else has to be binding the trigger on that first pull. You mentioned machine marks, where are you seeing this? Perhaps close up (in focus) pictures of the trigger group will help.

 

Also, if you separate the upper, set it to fire and run through the motions of pulling the trigger (don't let the hammer smack the bolt catch, put your finger in the way), hold the trigger back as you push the hammer back until it engages the disconnector, then release the trigger slightly till it resets then repeat, does that process cause the issue to replicate at all?

Okay, pictures and a video uploading.  It passes the selector test no problem.  Running as shown in the video below, no issues at all.  I ran dummies through it repeatedly trying to replicate the issue and narrow it down a bit.  

 

PSA complete upper, Full auto BCG, ATI poly Lower.

 

As long as the bolt fully cycles; no short stroking the CH- loading is a non-issue.  

 

The trigger issue arises when the trigger is pulled and remains pulled as the action cycles the next round.  In other words when the last round in a magazine is fired and the bolt locks back my finger comes off the trigger, I reload, release the bolt and that first pull of the trigger is heavy.  

 

What I figured out:

 

Be it right or wrong, I guess my "technique" (follow-through?) is to depress the trigger to fire, and hold it back until the gun settles back down.  Then I release the trigger almost as smoothly and slowly as I pulled it (I'm really into target shooting, slow paced, not a tactical pew pew).  As I release it I can feel it reset quite quickly (Like my PPQ compared to a 22/45) the fwd travel continues just a tiny bit and its done.  Whether I take my finger completely off the trigger at that point or keep it on there is no more forward movement, and the next pull is crisp, short and of nice weight.  The video posted below shows the hammer reset and then move just a hair more.  I highly recommend watching with sound as you can hear the reset and subsequent "click".

 

 

First click is the reset, second is a little bit of fwd jump of the hammer, and finally squeezing the trigger to fire on my thumb.

 

PS.  Click the first picture to link to the video I can't figure out how to embed it

 

 

And pics of the trigger group installed, best I can get

So is the trigger hard to pull the same way with the upper on and off? It isn't clear to me.

So is the trigger hard to pull the same way with the upper on and off? It isn't clear to me

 

Without the upper attached the trigger functions smoothly.  The issue is only with the FIRST round out of a magazine.  So I'm thinking its related to the BCG or charging handle/ bolt release in some way.  It would be a lot easier to deal with if it just didn't work at all.  Problem is the function is fine, its just like having two different triggers

given the polymer lower, is the upper putting any pressure on the lower, it might change the geometry.

 

Also, do you always load your mags withe same number of rounds? What happens if you load less in the mag? Wondering if the fit between upper and lower allows for the full mag to push against the upper and change alignment.

So, you're getting ready to shoot. You lock the bolt back, insert a loaded mag, use the bolt catch/BAD lever to send the bolt home and a round is chambered...

 

1. At this point, are you doing a press check by any chance taking the bolt out of battery?

2. After you drop the bolt, if you hit the forward assist, does the bolt lock in/move forward as if it wasn't fully into battery?

 

After the first round is chambered and you try to pull the trigger, this is when you're feeling the heavier trigger than normal. You squeeze the first round off, the rifle cycles and ejects the spent casing, bolt is pushed back far enough to strip another round from the mag, chambers the second round and this time the trigger is as smoothe as in your video without the upper installed. Is that correct?

 

Can you duplicate the issue any other way than with a live round? How many rounds have you put through the rifle so far?

 

At this point I would take the trigger assembly off and check for burrs or rough edges. Since the parts are new, check the BCG for any abnormal wear marks around the part towards the bottom ramp that cocks the hammer back as it cycles.

 

Where are you located? Maybe someone can meet you and try swapping out components to narrow down the culprit. I'd try your complete upper on someone else's complete lower first.

This was my first time to the range with it. First time shooting any AR. I loaded 1-3 rounds in each magazine I tried.

 

One round mags were tight on every pull. Two and three round mags were tight on the first pull and perfect for the rest of the mag.

 

I don't think it's the fit between the upper and lower. That seems quite good. If the issue were constant then I'd say it was one or the other. The fact that it's just the first round every time and not subsequent rounds confuses me. That's what's leading me to the BCG, CH, bolt catch.

 

I think I need to close the bolt. Feed a round by drawing the Ch back and letting it slam fwd and then seeing if the trigger pull is as heavy as if I use the bolt release to close the hold and feed a round from a new mag(now I'm talking out loud to myself on a forum, this hobby will make u crazy)

I'm guessing that your trigger geometry is changing based on loose pin openings or a flexing lower, and that the force applied to the trigger group is different when using the bolt release than when under normal operation. 

Is it me or.. Look in the last pic..... It didn't but look like the hammer is centered....

 

Are you sure your hammer and trigger pins are well seated and supporting the lpk properly

 

It looked the same to me. Which is why I suggested what I did. I've encountered drag from odd geometry due to cheap ass DIY "trigger jobs", and in some instances, you could get  the drag to disappear by applying a little lateral pressure on some components. But it was not an intermittent thing. 

I'm guessing that your trigger geometry is changing based on loose pin openings or a flexing lower, and that the force applied to the trigger group is different when using the bolt release than when under normal operation.

 

+1

 

Out of spec trigger group or lower. I'm betting on the lower.

 

ETA - Pick up one of these or any other reputable lower and try again.

 

http://palmettostatearmory.com/index.php/psa-blemished-safe-fire-lower.html