Posted this first in the retro section, but maybe it belongs here(IDK):

I've had a franken AR build since about 2001.  Colt 1/7 M4 style upper, PWA Commando lower.  It's in the original "Pre-ban" serial # range.     It took me long enough, to get around to jumping on the "I want something different band-wagon" and so I just decided to try to use that lower as a base for a dedicated coyote gun in either 6mm ARC or 6.5 Grendel.  

First things first, I thought I would start with a replacement drop in trigger.  Went with  a Rise Armament LE 145 as a good safe field trigger.  Go to drop it in, and NO - GO.  I would slightly start and that's it.

To Google I go, to search for what the standard spec receiver dimensions are, which lead me down a rabbit hole with no real answers.  Next, I pulled out my recently purchased PSA 300 AAC pistol as a reference.  Sure enough, the old PWA trigger well measures .681 but the PSA measures .685-.686

The trigger goes about .682 - like I said - NO GO in the PWA.  

What is the standard internal size for the trigger well?

Was mill spec back in the day tighter?  

Is there two different specs?

So, now I either return the trigger or buy yet another receiver for my coyote gun :(

Info in your OTHER THREAD