AR Build Help

[JFlowers]

I just built my first AR and I am having a small problem, hope someone can point me in the right direction.

The rifle functions correctly when manually cycled.

When fired, the rifle cycles but the trigger is frozen.

-- the bolt cycles, the case is ejected, a new round fed

Manually cycle and things are fine.

Remington ammo

AIM Surplus lower, CMMG parts kit, Colt 20" upper, Colt stock and buffer

My assumption is that the hammer is not locking back in the cocked position. But that is only an assumption.

[shooterready]

If you run the bolt manually once the trigger is froze does it free up?

[prreed10]

What trigger are you running?

It sounds like the timing on the disconnecter may be off.

Edited July 6, 2013 by prreed10

[fishsticks]

With the upper taken off and using only the lower does it pass a function check? There are lots of resources and threads on ARFCOM (Home of the Black Rifle) in the troubleshooting and Build It Yourself forums that cover how to do this.

[JFlowers]

If you manually run the bolt, things work just fine. Including after the freeze.

The trigger is the stock trigger in the CMMG Lower Parts kit.

Yes, the lower passes the standard function checks.

[3gungeezer]

Will it lock open on an empty mag when using live ammo? Sounds like it might be short stroking. Do you have access to different ammo, another upper or lower? If you do swap things arround and see if your upper and lower function on different ones.

[3gungeezer]

Also I find I have a lot less problems when I run my ARs really wet,(especially new ones).Lube everything really well and try again.

[Mark Gale]

With the upper taken off and using only the lower does it pass a function check? There are lots of resources and threads on ARFCOM (Home of the Black Rifle) in the troubleshooting and Build It Yourself forums that cover how to do this.

Removing the upper to function test is problematic...

Function Checks

[blue edge]

Will it lock open on an empty mag when using live ammo? Sounds like it might be short stroking.

+1

[JFlowers]

Yes. It will fire and lock open with a single round in the magazine.

[Mark Gale]

My assumption is that the hammer is not locking back in the cocked position. But that is only an assumption.

Yes, the lower passes the standard function checks.

I'm a bit confused by these conflicting statements. Sounds to me like your hammer is following. This issue can be diagnosed by swapping out parts, for known goods ones, in the following order:

Disconnector Spring

Disconnector

Hammer

Trigger

At this point, if your hammer fails reset, you'll have to look at your lower as the culprit.

[JFlowers]

Well, I got back out to the range this morning and I now know more. My hammer is resetting and is not following. But my trigger is not resetting. If you push the trigger forward you hear a loud click and then the rifle will fire again.

I am assuming the reason it works manually and passed most of the function checks was that the trigger would be released between manual cycles of the bolt, where its held back when actually firing.

Mark, it passed the Lower Only function checks. When I tried the ones you linked with the upper on, that's when I made progress on finding the issue. So, thanks!

[Mark Gale]

If you push the trigger forward you hear a loud click and then the rifle will fire again.

Getting closer...

It sounds like your hammer is being captured by the disconnector but it is not resetting. A successful reset would mean control of the hammer has been passed from the disconnector to the trigger. It sounds like there is a timing issue. If you are sure there is no debris in the trigger pocket, this problem can only be solved by parts that sit on the hammer and trigger pins. See my post above on the order of elimination.

[3gungeezer]

Well, I got back out to the range this morning and I now know more. My hammer is resetting and is not following. But my trigger is not resetting. If you push the trigger forward you hear a loud click and then the rifle will fire again.

I am assuming the reason it works manually and passed most of the function checks was that the trigger would be released between manual cycles of the bolt, where its held back when actually firing.

Mark, it passed the Lower Only function checks. When I tried the ones you linked with the upper on, that's when I made progress on finding the issue. So, thanks!

In that case you need to ensure the trigger moves freely in the trigger slot. I had to open up the slot on a lower I had when I installed a CMC trigger. The trigger was wider and it caused enough binding that it didn't allow the trigger spring to reset the trigger but it would reset like you said. Take your upper back off. take the lower only and with one hand prevent the hammer from over traveling and pull and HOLD the trigger. Next recock the hammer and release the trigger to see if the trigger will reset. if it doesn't push the trigger back forward and see if it resets if it does your trigger is binding and you have to find the cause.

Edited July 7, 2013 by 3gungeezer

[mpom]

All this done with lower and upper separated. As above, make sure trigger is not binding in slot cut just above trigger guard. If good, then issue is likely to be "disconnector timing". A good explanation and remedies are in the JP Trigger Installation instructions, available on the Net, and apply to you mil spec components. An easy fix as long as you go slow. Stone the disconn just enough to release hammer onto trigger and stop. Too much clearance can lead to doubling when trigger is released. Could be a weak trigger return spring, so worth trying that out if you have a spare.

[caspian guy]

I had an issue like this when using a heavy hammer spring on a RRA NM trigger group (on a 5.45x39 upper that needed more smack to set the primers off).

The face of the hammer that engages the disconnector and the disconnector were rough enough that if I pined the trigger and cycled the action, the hammer wouldn't come off the disco and the trigger didn't reset. If you cycled it without the trigger being pinned there was no issue. I lightly polished the engagment surfaces (without changing the geometry) and solved it for me.

Could also be a weak trigger spring, or incorrectly asembled .