AR Trigger Function Check FAILURE

[socal425]

Installed a new CMMG LPK on a new Aero Precision lower. During the trigger function check:

1. Verify that hammer locks to the rear when pushed back.
2. Verify that hammer pivots forward when trigger is pressed.
3. Without releasing the trigger, push the hammer back again and verify that it locks (caught by disconnector).
4. Releasing the trigger should not cause the hammer to pivot fully forward (caught by trigger).
5. Hammer will fall when trigger is pressed.

it failed at Step 4. Upon releasing the trigger, it released the hammer as well.

I have verified the install as well all parts being accounted for. I did swap out the FCG from a Spike's LPK and all functioned normally.

Any input as to why the CMMG FCG was not functioning correctly at step 4? Were the parts out of spec? Sure would appreciate any input.

BTW, I'll be giving CMMG a call on Monday for some recourse.

[wash]

Did you install the disconnector spring with the flared end down in the trigger?

[socal425]

All parts accounted for and installed correctly. Function check passed with Spikes trigger group. Thanks.

[tonelar]

Did you install the disconnector spring with the flared end down in the trigger?

Bingo

(I bet the spikes trigger has the spring in the right way)

[kcstott]

Double check all part installed correctly. If you still have the problem swap one part at a time until it goes away. Then you know which part was the issue.

[socal425]

Double check all part installed correctly. If you still have the problem swap one part at a time until it goes away. Then you know which part was the issue.

Did that with the Spikes group. Did not pass function check until the whole group was swapped out. So I'm wondering if the whole CMMG trigger group was somehow out of spec?

[kcstott]

Well it could be.
I'd call for a replacement

[socal425]

Bingo

(I bet the spikes trigger has the spring in the right way)

Both set ups did not come pre-assembled. I had to assemble myself and did so correctly. Did noticed that the disconnector spring was a tad shorter on the CMMG than the Spikes. However, it did not make a difference when swapped.

[wash]

The first thing I do when I get an LPK is add a shot of clp, make sure there are no burrs on the disconnector and then put together the trigger/disconnector spring/disconnector/trigger pin assembly together.

I'm actually kind of surprised that the better manufacturers still just throw parts in the bag.

I'm really surprised that so many people seem to mix up the bolt hold open and disconnector spring or they put in the disconnector spring upside down. It's so common that I heard about it before I even owned an AR lower.

Any way, if you have checked the disconnector spring and if it is installed with the flared end down capturing the spring inside the trigger, then you have a problem that is going to take a bit more investigation to diagnose.

Examine what your Spikes trigger does at step 4 and compare it to what your CMMG trigger does.

[Creampuff]

I posted these a long time ago, but hopefully this might help?

http://www.calguns.net/calgunforum/showthread.php?t=32797

[wash]

Don't send out a nasty-gram before you have identified the problem.

[bohoki]

i had one that did that on the bottom front of the disconnector there was a bit of bur from what looked like when punched it out i filed it down a bit and then it worked fine

[socal425]

Don't send out a nasty-gram before you have identified the problem.

No talk of "nasty-gram". Would just like to know what's going on with CMMG FCG. Besides that, everything else was a good fit and good install with the other parts of the LPK.

With the Spikes FCG, it was GTG. I believe it's safe to say that something is at issue with the CMMG group. Thanks for your input.

[Seesm]

Swap the disconnectors? I see alot of lpks come with funked up disco's It is something simple for sure.

[socal425]

Swap the disconnectors? I see alot of lpks come with funked up disco's It is something simple for sure.

Did a closer inspection of both CMMG and Spikes disconnectors. CMMG measured 1.4mm longer than Spikes. Thought I had swapped those parts to test, but obviously missed that test while swapping everything else.

Sure enough, using the Spikes disconnector with the rest of CMMG FCG, it passed the function check. Thanks to all and to Seesm for your input. Will be giving a call to CMMG for a new and hopefully functional disconnector.