Do you guys have first hand experience with accuracy improvements by truing the receiver face and bedding AR barrels?
Care to share? I'm going to pull a few of my AR's apart and give this a whirl and see if it has any effect.

-ZA

I slapped a Compass Lake Engineering Bartlien on a standard forged mil spec upper and it shot 0.74 moa on average.

I removed the barrel, trued the face of the receiver on a mandrel between centers on a lathe, and bedded the barrel to the upper using a wax release agent on the upper and JB weld as the bedding compound on the barrel extension. This allows the barrel to be removed when it's shot out and the receiver is clean and ready for the new barrel. A dowel and mallet must be used to remove a barrel bedded in this manner.

After facing and bedding the rifle shoots slightly under 1/2moa with no POI shift regardless of temperature.

I've accurized many ARs in this manner but the above is the only back to back test I've done. The results were good enough to satisfy my curiosity.

I made a jig for my Aero M5 upper on my lathe. I trued the receiver face which was about 0.002-0.003" out. Mounted up my proof research barrel and get pretty good groups (around 1/2 moa) using FGMM. I don't know how much it helped but it gives me peace of mind.

I had one, a spikes receiver shooting hard left. Trued it up and sights centered then. Always do the bedding thing now too from the start.

This.  I do continue with the face-truing mandrel just a bit more until all the anodizing is gone.  That way I know the face is completely flat.  Those who criticize this method claim that the face may not be exactly on-axis, concentric with the center line of the upper.  They miss the point.  The goal here is to be flat.  Usually, you are also on-axis or close to it if the mandrel is high quality.  But the point is to be flat, so that the barrel extension shoulder makes full and even contact with the face as the barrel nut pulls them together.

And, yes, use the shim stock all the way around, as needed, to remove any lateral slop.

Works for me.



This Lilja barrel and trued receiver required no shims.  Very tight fit.

It depends on how you define benefit and diminishing returns.  In most cases barrels are not the the problem when it comes to ARs - it’s the receiver.  Many companies do not have exacting tolerances when it some to what they put out.  An average off-the-shelf AR upper could benefit from this process, but if you buy a quality high-end receiver like with JP, you will see very little benefit from any truing or bedding action; particularly if you were to match it with a JP barrel designed to interface with that receiver.  Especially right now, the AR market is flooded with companies that are pumping out rifles to meet demand and QC had tanked.  Every time there’s a gun panic, QC drops significantly with all but the top tier companies.  We saw it in 2008 (Obama) and again in 2012/2013 (Sandy Hook) and we’re seeing it again right now.  If you don’t buy a rifle or components from a top tier company that has high standards for their QC, you will see enough variances in tolerances that truing and bedding may be necessary to achieve the best and most repeatable accuracy.

JP Enterprises upper receivers are thermal-fit.

...

I use stainless steel shim stock for thermal fitment.

So are SOLGW and BCM. This is the way to go. I fought with a MUR upper that was sloppy, thinking that would be the upper to use for a precision build because of the marketing behind it. No more. Thermal fit if it's intended purpose is precision. After you see how they fit, you will ask yourself why you ever messed with shim stock and Loctite 620.

MUR's tend to be on the larger side of spec regarding the receiver snout's i.d. Everyone I've seen has been.

I’ve got several MUR uppers I built and had to thermal fit the barrel in every one of them.

Reciever facing probably has more of a benefit to making sure the barrel is pointing straight out of the receiver. When we we use to shoot iron sighted rifles, it was sometimes the case that to zero, it required quite a lot of windage. Squaring the receiver face would often cure that. Of course then they came out with windage adjustable front sights, so receiver facing wasn't that important.

Making sure the barrel extension fits snuggly into the upper is absolutely important and shimming a barrel extension is one way of doing that. I've done numerous barrels with shims. Watch my video for a more thorough explanation.

B

It makes a difference when the barrel is thermal fit for sure.  Who makes a good truing mandrel or lathe tooling?

my limited experience:  Brownells, PTG, X-Caliber for the Aero M5E1 Enhanced.

There isn't any way for more to know if I got an accuracy improvement simply because I didn't shoot my rifles prior to squaring up the receiver face.

What I do know, is iron sights and scopes are more aligned when I true the receiver prior to installing the barrel.

It's not unusual for the rear irons to be only a couple clicks off mechanical zero when I true the receiver face.

https://www.ar15.com/forums/precision-rifles/Hellbender-s-a-k-a-Lostinthewoods-Guide-to-the-Ultimate-AR-fixed-/4-6919/