I've done it.
I used a Brownells tool on my Sionics OEM upper. Did the following:
-lapped the receiver
-glued the barrel extension using green loctite
-"floated" the gas tube
I did a before /after comparison with a few different loads. I saw a massive improvement with some loads(ADI, Creedmoor, Hornady) and almost no change with others (IMI, Wolf Gold, PPU).
In my sample of one the loads that shot "well" beforehand didn't change much. The match loads which shot poorly originally improved by quite a lot.
If I were building a new upper I would do it by default.
I'd be very afraid of galvanic corrosion if the anodic coating is removed from any surface that contacts steel or stainless steel.
If you're using/buying from a quality manufacturer I wouldn't think its necessary. That should be checked in the QC process. At least I would hope so.
I was sloppy in my description. It only touches/laps the upper receiver face. None of the internal (including the internal interface of the barrel extension and receiver) are affected.
This site shows how it works.
Chris
Last edited by mtnbkr; 07-08-2019 at 06:42 AM.
I suppose it depends on the original specifications. I wouldn't think the original mil-spec would be that detail-oriented. To be honest, I'd only consider this useful (in a theoretical sense) for target rifles where group size and consistency are the goal.
It appears to be a commonly accepted step for target rifles, which is why I gave it a try on my 20" build.
Chris