How critical is trigger pocket depth ? - Page 1

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[ARCHIVED THREAD] - How critical is trigger pocket depth ?

Posted: 3/10/2019 12:44:32 AM EDT

So spec for FCG pocket shows 1.249”. In milling my 80 lower with the jig, I got to roughly 1.243” on average. I took 4 measurements in different locations. Minimum was 1.240 and max was 1.248”. I absolutely will be test fitting before having it coated, but I’m not that interested in reassembling the jig all over again.

I’m a little concerned if I try to adjust the router for that fraction of extra depth I’ll end up milling past the 1.249”.

Posted: 3/10/2019 4:21:50 AM EDT

[#1]

use epoxy and reroute? i dont know but the depth of the pocket will determine how much the trigger can be pulled, so if its not deep enough the trigger might not have enough room at the front to release the hammer, and deeper in the back would change the angle of how the trigger rests, therefore affecting the angles on the engagement points between sear, trigger and hammer. but not sure what how much .005 will affect things. id just install trigger group and just make sure it functions

Posted: 3/10/2019 6:33:22 AM EDT

[#2]

I wouldn't try to reset it up and recut it with a router. Maybe with a milling machine.

You 'should' be ok.

You could always use a dremel to sand a little bit off of the bottom. Use a marker to color the bottom so you can see where you've sanded since it is a blind pocket.

Posted: 3/10/2019 7:30:44 AM EDT

[#3]

I wasn't deep enough on one i did. This resulted in the selector not fitting correctly.

Not positive but a little to deep I wouldn't think would effect it much the trigger pin will set your hieght. I think we've had a couple members completely go through the bottom of the FCG pocket and remedy it with a contained trigger group like a CMC.

Tolerance is prob +/- 0.010 anyways.

Posted: 3/10/2019 11:15:00 AM EDT

[#4]

Quote History

Quoted:
I wasn't deep enough on one i did. This resulted in the selector not fitting correctly.

Not positive but a little to deep I wouldn't think would effect it much the trigger pin will set your hieght. I think we've had a couple members completely go through the bottom of the FCG pocket and remedy it with a contained trigger group like a CMC.

Tolerance is prob +/- 0.010 anyways.

View Quote

1.249 + .010 inches

That said, if there is enough room for the trigger to disengage the hammer, you're good.

Posted: 3/10/2019 1:34:40 PM EDT

[#5]

I have never measured and never had a problem. I think it is very forgiving. Keep in mind the hammer/trigger index off the holes, not the bottom.

Posted: 3/10/2019 2:23:07 PM EDT

[#6]

Quote History

Quoted:
I have never measured and never had a problem. I think it is very forgiving. Keep in mind the hammer/trigger index off the holes, not the bottom.

View Quote

That’s what I remembered but wasn’t sure if the trigger needed enough bottom room below the pin to move and disengage.

I’m going to leave it and give it a fit / function test.

Thanks all.

Posted: 3/10/2019 2:25:40 PM EDT

[#7]

If it is two shallow you will know it, the trigger will not release the FCG, a bit to deep won't make any difference really. There are published specs with tolerances specified, but in real life they are really pretty loose, you can get away with a lot on the AR and still have a fully operational gun.

Posted: 3/10/2019 5:28:33 PM EDT

[#8]

A depth of around 1.210" you'll start to see problems....

Posted: 3/10/2019 5:36:16 PM EDT

[#9]

Quote History

Quoted:
I wasn't deep enough on one i did. This resulted in the selector not fitting correctly.

Not positive but a little to deep I wouldn't think would effect it much the trigger pin will set your hieght. I think we've had a couple members completely go through the bottom of the FCG pocket and remedy it with a contained trigger group like a CMC.

Tolerance is prob +/- 0.010 anyways.

View Quote

I did this

First I cut it too shallow. Went back to cut it deep enough and forgot to set my stop. Suddenly realize I'm out the bottom. Ended up cutting a sqare hole and putting a rise trigger pack in it.

I should probably throw it away, but it shoots fine so I would feel bad if I threw it out.

Posted: 3/11/2019 5:14:23 AM EDT

[#10]

It’s fairly critical if you like modular (“drop-in”) triggers. I’ve learned to finish the receiver, wipe off the flakes, and then set my trigger in to see the fit.
On my latest build I needed to make a final shallow pass with the router through the FCG pocket to fit the trigger I wanted.
Turned out fine.

Posted: 3/11/2019 12:17:20 PM EDT

[#11]

Quote History

Quoted:
It’s fairly critical if you like modular (“drop-in”) triggers.

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What Trigger? My experience is the opposite. For example on the Timney, going too deep does not matter. And not going to the correct depth (within reason) does not matter as it still fits.

Posted: 3/11/2019 12:29:04 PM EDT

[#12]

So I cleaned everything up and just installed a safety selector and an MBT trigger. The hammer was a little tough to get aligned the first time, but it seems to work. Safe works, semi works...trigger felt just as clean as all my other MBTs.

So good to go you think? Off to the anodizer?

Posted: 3/11/2019 12:45:58 PM EDT

[#13]

Quote History

Quoted:

What Trigger? My experience is the opposite. For example on the Timney, going too deep does not matter. And not going to the correct depth (within reason) does not matter as it still fits.

View Quote

I think he meant the other extreme, not being milled deep enough for the "housing" on a drop-in style trigger pack.

Posted: 3/11/2019 2:22:12 PM EDT

[#14]

Quote History

Quoted:
So I cleaned everything up and just installed a safety selector and an MBT trigger. The hammer was a little tough to get aligned the first time, but it seems to work. Safe works, semi works...trigger felt just as clean as all my other MBTs.

So good to go you think? Off to the anodizer?

View Quote

As long as there is some free play -overtravel- after the trigger is pulled, you should be GTG.
And you should be able to fit the trigger without removing the fire selector.

But even so, if the trigger has some free play in both directions, it should be good.

Posted: 3/11/2019 2:34:00 PM EDT

[#15]

Quote History

Quoted:

As long as there is some free play -overtravel- after the trigger is pulled, you should be GTG.
And you should be able to fit the trigger without removing the fire selector.

But even so, if the trigger has some free play in both directions, it should be good.

View Quote

All MBT's require the safety be removed for installation.

Posted: 3/11/2019 6:56:21 PM EDT

[#16]

With modular triggers, what I've experienced is the FCG pocket being too shallow, and you can't get the pins in (the trigger module is sitting too high).

You can then file the bottom of the modular trigger body (I've done that), or you can plan ahead and fit the trigger in before you put everything away.

The latter choice is what I do now.

Posted: 3/11/2019 9:39:45 PM EDT

[#17]

Quote History

Quoted:
All MBT's require the safety be removed for installation.

View Quote

Yeah, I found this out. Overall it fit pretty good and I’m satisfied with this being my first 80 lower

Now I’m Working on knocking off the burs and putting a small small chamfer on the trigger / hammer pins holes.

[ARCHIVED THREAD] - How critical is trigger pocket depth ?

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