Finished milling out my 1st 80% lower using the 80% arms Easy Jig.  They have a template which you set your end mill depth and I milled till I bottomed out the end mill in the included template.  The end of the mill was physically touching the template.



Put all my tolls up and spent 15 minutes sweeping out all of the aluminum that the router threw all over every inch of the garage.  Put the ruler to my lower and it looked like I was a ~1/32nd off of 1.25.



Pulled out my calipers and confirmed the reading of 1.2230.



I know MilSpec is 1.249 +/- 0.01 so I'm still 16 thousands from being into tolerance.  I don't have a LPK to make sure it's functional.  Do I need to back the car back out of the garage and dig my tools back out and put the lower back under the knife and remove that few thousandths?  How exact does the FCP need to be?

I doubt it functions.

0.027" is likely enough to prevent the sear from releasing, as the forward part of the trigger (which is the sear) will not be able to drop out of the sear notch on the hammer.  It might work, but I'm betting you'll find that you cannot install the hammer normally, and if you do manage it by rocking the hammer back, it probably won't release.

I'd give it another pass, as mentioned, I doubt it would function as is

Throw in a spare FCG & safety selector (without detent & spring) and function check. That should tell you...



...also, interesting that you left the material between the FCG pocket & rear pocket...

This is my first build and I don't actuly own any lower parts yet . Ment to say if I actually had a lpk I would try it out but as is I guess I will break out the tools and give it another pass.

Saw where people left that material on there with receivers that have the rear takedown area already milled. Adds a bit of weight but not necessary to remove it.  Decided to save myself some time and leave it.

It's becoming fashionable on ARFCOM.  He's the 2nd chap in the last week to post photos.  Marginally strengthens the lower, not so important on aluminum builds, but probably a small help on plastic & wooden lowers.

I think it is becoming fashionable because Tactical Machining sells their looters that way now.

I mill out the bridge because I have faith in Nolo.

THIS!

I have a few lowers like that and have left the bridge. It doesn't matter as long as the upper closes on the lower and functions. Plus it's one less step you have to do and I'm kinda lazy like that.