I'm new to all of this and would appreciate any input prior to live testing.  This is the only AR-15 I have access to so I don't have any frame of reference beyond the Internet.  I milled and drilled my first at lower and during assembly found that I could not quite insert safety selector with the hammer cocked.  The amount of rear trigger assembly intruding in the selector hole was small but enough to cause the selector to stop.  Selector inserts fine with trigger group removed, albeit snugly.  Just on a lark, I decided to improvise and insert the selector first, angle it to 1 o'clock position and slide the trigger group in under it.  I completed assembly and test trigger function, all seems to work as described in various assembly and testing guides.  The safety functions correctly as well, albeit feeling very snug.  The only thing of note is that the trigger is tight, doesn't travel very far to release the hammer.  I've tested this repeatedly with a block, then with the rifle fully assembled.  My only concern is that something go wrong during live fire. 

My pocket is ~ 1.22 inches deep, all else is spec.  I'm using an old set of calipers though, so I could be 1.21 or 1.24 depending upon their accuracy (and my ability to read them with my over 40 eyes). 

I appreciate any thoughts or advice you may have.

If the FCG function tests properly as you describe, then you should be more than safe to proceed to live fire testing.  Be safe and only load partial mags at first Incase you experience any doubling or such, but there is little chance of anything catastrophic occurring.

Excellent, thank you!  Is this type of tight fit and juggling of selector and trigger group completely abnormal or is it within the 'norm' for AR-15s?

I admit I like the feel of the trigger, coming form shotguns and handguns.  That being said my primary concern is metal expansion on heating so I will be loading single, then small mags to be sure when testing.

You need to mill deeper. I had the same issue about 3 months ago. I set my router,to mill out in small increments, past the manuf. depth gauge. In 2 passes everything fit.

I doesn't take much man. Small passes

"Past mfg depth gauge". strikes a chord.  I am using a mill bit with a rather thick black line on it to mark correct depth from mfg.  I went down far enough that the bottom of the line just dipped below the jig.  Is this what you mean?
I wondered if I should've gone deeper so that the line was perhaps bisected by the jig rather than just below it.

This +1, sounds like the pocket is just a smidge on the shallow side, it should be 1.249" if I recall correctly.

I would take the pocket to 1.25 and then everything will fit and function correctly, you are a tiny bit shallow on the FCG pocket.

Wait, what? They expect you to work with measurements that require going 3 places past the decimal while relying on just a line drawn on the endmill? You have got to be kidding me. LMAO

a very fat line on the end mill, albeit engraved yes. I had a set of calipers (a must) I used to measure depth but realized later that they were off.
At this point I am going to buy a much better caliper, disassemble and measure again and mill deeper until I'm closer to the spec.

Thanks!

Your jig didn't include a depth gauge?  Modulus' jigs and the 80% Arms EZ jig all do.  The Modulus ones seem to work fine.

I used the Polymer80 G150.  Besides the issues drilling pin and selector holes using the plastic jig (difficult enough that I needed to carefully shape my selector hole to fix angled entry)
and the tendency for the mill bit to grab the aforementioned holes during milling despite taking 1/8 inch bites it was far easier than I'd expected.  One of these days I'd like to
do an aluminum but then again I may just buy an Aero or Anderson.  I really wanted to do this just for the sense of accomplishment,
but it isn't an accomplishment until it safely fires :)

While I understand the exhortation to mill deeper, are there any inherent dangers in leaving it this way and testing?
i.e. If it successfully fires a full magazine semi-auto, is there any likelihood that at some later time it may fail to catch the sear and fire more than one round?
I do like the trigger travel and feel and I do like the feel of the safety as it is quite tight on the rear of the trigger assembly when in SAFE.

Had a simliar problem on my first build. As others have said you're probably just a hair too shallow. I milled mine down a little more and everything went together great.

"While I understand the exhortation to mill deeper, are there any inherent dangers in leaving it this way and testing?
i.e. If it successfully fires a full magazine semi-auto, is there any likelihood that at some later time it may fail to catch the sear and fire more than one round?
I do like the trigger travel and feel and I do like the feel of the safety as it is quite tight on the rear of the trigger assembly when in SAFE. "

I would think that as long as your holes for the trigger and hammer pins are in the right spot you shouldn't have a problem, but I'm no expert.

Thanks everyone for the input and advice!  I'll post back a reply after I get the time to test the build.  But I will be using a set of digital calipers to make sure
I'm closer to tolerance than my analog said I was or I will mill a bit farther.