Grendel problem

I’m having a problem with a recent purchase.

I bought an upper receiver in 6.5mm Grendel by AR Stoner (Product #: 509828). I also bought a couple of Grendel magazines in including both 25 and 10 round models, and some Hornady 123gr SST ammo (Product #: 820397) for it. I mounted an AR-STONER Cantilever Scope Mount (Product #: 114583) on top the receiver. I attached the upper to a lower receiver I’ve used successfully for a couple of different after-market uppers, in both 223 Remington and other calibers.

I went to the range to sight it in and ran into two problems.

Problem 1) At 25 yards I’m getting 4-shot groups about 1.5 inches across. For quality factory ammo, and ideal range conditions, that is… unexpectedly large, shall we say.

1.01) Even when I hand-chambered single rounds to avoid damage from chambering with a rough feed ramp, the grouping was not noticeably smaller.

1.02) They were not keyholing or showing any obvious “small group with a flyer,” they were a consistently large group, typically about 1.5 inches on extreme spread. Again, this is only 25 yd.

1.03) I don’t have any other rifles chambered in 6.5 Grendel to test the ammo with to make sure it’s not a REALLY bad batch.

1.04) Nor did I have a second brand or load to test to see if it was somehow related to that particular upper receiver + ammo combo.

1.05) However, it’s possible that the large group is related to the second problem:

Problem 2) Failure to extract and feed reliably. After a couple of problem shots, I went into “test and diagnose mode,” and here is what I found:

2.01) If I lock the bolt back, seat a magazine with a single round (and I tried four different magazines, both metal and polymer, all in excellent / new condition), and hit the bolt carrier release, it will successfully strip the round from the mag and chamber it.

2.02) However, when I fire it appears to cycle the action, but it usually fails to extract, and usually comes to rest with the bolt forward (not locked back on the empty mag, but sometimes it does lock back).

2.03) If I pull the charging handle back and let the bolt fly forward from all the way back, then hit the forward assist, then manually pull the charging handle back, it will extract, but it’s very stiff: much more than I’d expect from just being “new,” and yes, I’ve broken in several AR-type rifles and uppers before, as well as used many of them new and well-used both in and out of uniform.

2.04) If I seat a magazine with more than one round, it will chamber and fire the first one fine, but it will fail to extract/eject and try to chamber the next round, jamming the tip of the next round into the back of the still chambered (but empty) expended round, resulting in a badly damaged tip and/or severely marred bullet ogive.

2.05) I only had the one type of ammo or I’d have tried others.

2.06) Obviously, it was delivered “dry,” pretty much oil-free. I added some lube on the appropriate surfaces, and nothing changed, so I added it more liberally in more places, still no change.

2.07) I removed the bolt carrier group to test to see how well the extractor grabbed empty brass, and it appeared to work fine.

2.08) If I drop a live round into the chamber, and tip the barrel upward, the round drops free with absolutely no problem.

2.09) If I inspect the fired brass, they appear to have both longitudinal scratches (but not in any noticeably consistent pattern), and circumferential scratches. The case mouth on most of them are out of round, and many of the rims look more well-used rather than pristine but once-fired. I’m using a brass-catcher (Product #: 800355), so I’m sure it’s not from hitting the ground and rolling around and being abused post-ejection.

2.10) Inspecting the ammo that I didn’t shoot from the same box, it looks as pristine and scratch-free as you’d expect a quality factory product to appear.

2.11) I thought out loud about the problem at the range, and solicited thoughts of ideas from others there; their suggestions were bad ammo (didn’t have any others to test), insufficient gas from the gas block to push the bolt all the way back (not adjustable, don’t have a spare, don’t think needing to buy something to make a “complete” upper work is reasonable), or something wrong with the buffer (works fine with all other uppers I own).

2.12) An internet search on the problem when I got home indicates gas block (most likely), chamber needs polishing (next most likely, causing too much friction for normal extraction), feed-ramp polishing needed, or buffer problem (unlikely).

2.13) Upon close inspection, there are noticeable copper deposits on the tops of the lugs by the feed ramp. I would guess that is at least part of the cause for marring seen on both bullets and brass.

2.14) So, before I write a public review of the product on my blog or at, or buy more parts or try home gun-smithing randomly on a new upper that should work fine as-is, I thought I’d give you a chance to help me out and get this thing running like I would expect it to be able to.

2.14) In a previous career I did tech support (high-tech), so I know much a good tech support experience can make up for a bad initial product experience, or a bad one can cement a negative impression. I look forward to your suggestions, exchange policy, or whatever you have to offer by way of potential solutions.