Not really. I guess I was just going to see if a build could shoot any better than a Colt HBar Elite. The first 100 rounds shows that it will. My range is limited to 300 yards, but if I fix up portable targets I can move beyond my boundaries.
Yes, it is possible to lap the receiver face of the Aero M4E1 receiver. This company makes the appropriate lapping tool: https://www.x-caliber.net/bart-20?fb...SF0tnTOey3B0eg
There was another company (g and g rifle works) that also made a similar tool, but their website is no longer available so I have no idea if they are still in production.
I did an Aero M5E1 ("308" large frame upper) using the afore-mentioned X-caliber tool. The tool worked like it's supposed to. I know it's not exactly what you asked, being the large-frame AR instead of the M4E1, sorry. Figured it's kinda close.
I'm really late to this game, but, I check it on each and every upper. NO I don't use the Drill Powered tool. I built a tool years ago that is a fixture with .0001" TRO. I place the Upper on this jig, insert it in a 4 Jaw Chuck adjust of .0001 TRO at an indexing area just beyond the Barrel Stop Ring Mating Surface. Once "zeroed" i can now check Concentricity and Perpendicularity of the Receiver Flange to the Long Axis. Here's the important part, first I measure. To quote an old James Gang Tune "Garden Gate" - "The captain’s in the chartroom Navigating on a star, Can’t know where we’re going 'Cause he don’t know where we are" I also check the CL of the rail for Parallel to the Long Axis of the Receiver (both axis). It's surprising the number of Uppers that are off in this dimension. I guess the concept here is "they got windage and elevation adjustment". But, on a Billet????
As to the original question I have found big $$$ Billet uppers off of perpendicularity by .003". I have also found $39 Mil-Spec perfect.
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