Chamber hone for 6.5 Grendel

Via email from Rolf:

I know that several boomershooters use the 6.5 Grendel. I was having problems, and suspect a rough chamber might be the culprit. (Still awaiting a reply from Midway, where I bought the upper, as it’s a MidwayUSA house brand, before I do anything like home gunsmithing). I went looking for a chamber hone that would be right, and could not find one, and saw contradictory info on the web. So I emailed the company (Brush Research) that makes the Flex-Hone chamber hones to ask what the correct one might be. I got this prompt reply this morning. I’m pretty sure that they’d be OK with posting the info on a popular shooting-related web-site such as yours, if you want to post it for any of the Grendel shooters out there who might want to know.

From: Technical <technical@brushresearch.com>
Sent: Monday, July 13, 2020 9:21 AM
Subject: Re: [#479759] New Technical Inquiry Home

Hi Rolf,
Thank you for contacting us regarding chamber hones for your 6.5mm Grendel. We have made these for the Grendel before only they aren’t visible on our website or literature.

You’ll want to order part ID 12809  for 400 grit SC abrasive or part ID 12810 for 800 grit SC abrasive.  The following distributors can order this for you in Washington state. Simply contact them and ask them to order up the part ID’s provided:

APPLIED INDUSTRIAL TECH
4021 6TH AVE S.
SEATTLE WA 98108
(206) 223-5255

FASTENAL
9320 15TH AVE SOUTH
SEATTLE WA 98108
(206) 762-0297

Let me know if you have any other questions we can assist with.

Regards,

Brush Research Manufacturing Co., Inc. 
4642 Floral Drive, Los Angeles, CA 90022
Phone: (323) 261-2193 ext 703
Fax: (323) 268-6587

11 thoughts on “Chamber hone for 6.5 Grendel

  1. What was the problems? Chambers are supposed to look rough. If it’s messed up that bad, Send it back. If it’s an AR. There’s a ton of things it could be. Most are easy fixes.

    • Short version – really shitty accuracy (1.5″ groups at 25 yards with good ammo for initial sight-in), brass and bullets getting badly dinged up while chambering the round, and failure to extract with any reliability, resulting in either a simple fired round with the brass still in the chamber, or it attempting to double-feed. I think the feedramp is pretty rough (damage to round while chambering), and the chamber is to “sticky” resulting in too much friction to extract fully, so it short-strokes. The ejector appears to be working OK as near as I can tell. I have learned that this particular brand is sort of a crap-shoot on quality; some are great, and a very good deal at the price, and others are… not. https://www.midwayusa.com/product/1020799661?pid=509828 this one, on an even better sale (well, lower price, anyway).

      It’s also possible I’ve totally misdiagnosed the problem – any and all thoughts or recommendations welcome.

      • Do you have a borescope? Or access to one?

        You won’t really know what your chamber looks like without one.

        If you don’t, the $50 Teslong Rifle Borescope on Amazon is pretty good. It attaches to either your phone or computer and has a decent resolution.

        I got one because of the recommendation from Chad Albrecht at School of the American Rifle in one of his recent videos.

      • Accuracy with good ammo. Bad barrel. Cartridges that are fat, for the feed length generally get beat up by the bottom post of the star chamber. Even on 5.56 you will see a big scar down the side of the case as it passes into the chamber. If the shoulder contacts the post at the same time it’s being held tight by the feed lips on the magazine. It will dent shoulders and scar the cases pretty bad.
        It might have something to do with your accuracy problem in the longer 6.5 bullets add leverage, and bend the case/bullet just enough to not enter the chamber straight?. Contacting the roof of the chamber as it pops loose of the magazine.
        Short strokes, double feeds are almost always gas problems. As the AR system is somewhat delicate the initial part of the power stroke. The first 1/2″ of movement. As it unlocks the bolt, and starts it’s reward travel. Take anything out at that point and the bolt will many times go back enough to spit out the empty case. But not far enough to pick up the next round. Sometimes the case just pops loose and drops on top of cartridge that’s being picked up. Also, As the case exits the upper, It will have turn 180 degrees so that the case mouth is smashed against the brass deflector, Damaging it.
        Diagnosing that problem is two fold. If it has a mid-length, or rifle length gas system. That shouldn’t be the problem. Carbine length will over gas. As the gas cycles back so fast that it tries to extract the case while it’s still pressurized in the chamber. Thus stealing from the power stroke. This will show as a bright smudge on the base of the case. Even as a sharp ridge.As the case head is being twisted against the ejector plunger while under pressure. Ideally, chamber pressure is at zero when extraction begins. You will need an adjustable gas block.
        Next check your gas rings. With the bolt/ bolt carrier fully extended. It should stand up on it’s own. If it collapses down under it own weight, change gas rings till it stand on it own.
        Believe it or not. Some of it could be your magazines. If the feed lips are bent down to much, it will hold on to the cartridge to long through the feed process. Also, if the magazine lock hole is to far down, it will force the feed lips against the bottom of the bolt. Creating drag.
        The only chamber problems I’ve seen were someone chrome plated metal shavings into a chamber. And someone tightened the barrel nut to the point of jamming the bolt face into the front of the chamber. All on very expensive guns. So don’t feel bad about being ,”thrifty”.
        Hope that helps.

  2. Might be useful to do a ferrocast; I had a varmint rifle in 222 Magnum once that defied all attempts at accuracy (I was the 4th owner of the rifle in 2 years….). Turned out the chamber was very slightly off center from the bore, caused by the chamber centerline not being perfectly coaxial to the bore centerline, probably caused by a tooling alignment error during chamber polishing; just a thousandth or two can make a huge difference. It was also “long throated” which didn’t help, either.

    A ferrocast will also show you what the lede and throat look like.

  3. It sounds like there might be more than one issue.

    Have you checked the chamber with a go/no-go gauge set? If it fails that, the upper should go back, period. A too short chamber could explain some of the issues.

    What magazines are you using?

    How well does it feed and extract dummy rounds / snap caps?

    Have you checked the muzzle crown for burrs? Perhaps check the flash hider for grazes, or try shooting it with the flash hider off?

    • No, didn’t check with a G/NG gauge. Don’t have one for it. Tried four different mags (metal and polymer, ten-round and standard capacity, three different brands). don’t have 6.5 Grendel snap-caps, but if I manually drop one into the chamber and tip the barrel up, it appears to fall all the way in, and drops out freely. Any muzzle issues might affect the accuracy, not the extraction / double-feed, but in any case it looks good. The shells are getting dinged on the way in by the look of it.

  4. As the owner of a Midway upper (350 Legend), I am now very happy with mine. It’s my second one. The first one damaged rounds going in to the chamber if they even went in from the magazine because of the rifle’s action. Accuracy was OK for me. Cycling was a no go.
    I recommend returning yours to Midway. They were great about mine; easy, no questions asked, fast turnaround and the second upper is working well.
    I’m not a long range accuracy shooter, but honing a chamber sounds like a very fine adjustment for fractions of MOA results. Your issues seem to need broader fixes.

    • Yeah, I’m leaning that way (returning it). Never had a problem before with their stuff, maybe it’s time to test the return policy.

      My thinking was, after a bunch of testing, that a bad feed and sticky chamber would result in the rounds being marred and out of concentricity (resulting in inconsistent accuracy), then when the extraction fails the next round gets jammed in on a double-deed and further mangled, reducing accuracy even more. A polymer-tipped round with deep scratches and its tip bent over at 30 degrees will not fly true.

      • That sounds good, let Midway get you one that works like it should before you need to adjust stuff. If you’re within their time frame for returns, I heartily recommend their process.

        • Filled out the RAM stuff, will drop it in the mail today. With any luck the replacement will work as expected.

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