New AR Build Issue

[ac6916170]

With an upper receiver lapping/squaring tool. Just because I don't post alot doesn't mean that I haven't built more than my fair share of "ACCURATE" AR's.
http://www.brownells.com/gunsmith-t...16-upper-receiver-lapping-tool-prod20220.aspx.

 

[MachIVshooter]

With an upper receiver lapping/squaring tool. Just because I don't post alot doesn't mean that I haven't built more than my fair share of "ACCURATE" AR's.

Unless you have a sloppy fit between barrel extension and receiver, lapping the face of the barrel extension housing won't change receiver bore to barrel extension alignment. And if your barrel extension to receiver bore fit is not tight, lapping the face is a band aid.

It also won't help one bit if the issue is with the barrel extension concentricity inside to outside, barrel extension lugs or the bolt lugs.

More to the point, a few arcseconds of misalignment between barrel extension and receiver bore wouldn't matter when the bolt itself has as much as .008" "wiggle", even when brand new.

It should also be noted that an inexperienced assembler can easily do more harm than good with tools like this. Real easy to increase the bore size at the front and create a taper with compound that works its way down when you're driving the thing with ordinary power tools. I wouldn't even want the average " gunsmith" trying to use that on anything I own. It ain't far removed from chamber polishing with a dremel (except that your taking bigger bites in softer metal with larger and more powerful tools)

 

[WinThePennant]

Might be a stretch, but are the feed ramps (assuming it has the M4 feed ramps) lined up right? Of course, that won't affect ejection. But, having two problems at once is not exactly unheard of...

 

[.Scarecrow.]

Extraction is no longer a problem, BCG is extremely smooth now. Sounds to me like the wear on the lugs isn't much of a deal.

 

[.Scarecrow.]

I have looked at the idea of squaring up the receiver. It sounds somewhat interesting, and yes I know the consequences if something goes wrong.

 

[MachIVshooter]

I have looked at the idea of squaring up the receiver. It sounds somewhat interesting, and yes I know the consequences if something goes wrong.

My suggestion is, unless you can dial indicate the bore of the receiver to a quill on the vertical axis, hold everything completely rigid, and apply constant even pressure, don't. Basically, you need a vertical mill to ensure that you'll actually be improving anything.

I've built at least 2 dozen uppers, have yet to see a barrel extension mating surface that needed to be worked. Uppers are almost all Cerro forge or Anchor Harvey forgings, but have come from many sources, including PSA, DSA, DPMS, Anderson and others.

Besides which, it does not seem that you have a problem after all.

 

[.Scarecrow.]

I see your point Mach, I'll keep that in mind before I make a final decision.