Don't believe the rifle type matters, but it's a DPMS GII Recon.

Noticed awhile back I was seeing slivers of metal in the receiver area when I was taking it down, but didn't know where they were coming from.

Upon close inspection, the bolt carrier is recoiling back so far into the extension, that the two (of the four total) lower "rails" on the carrier that guide it in the upper receiver are hitting the extension tube, and removing aluminum where they impact.

Quarters inside the tube, or a short spacer inside the spring don't allow the carrier to move back far enough for the bolt catch to work.

I don't see a fix for this other than to let it clearance itself. Am I wrong? This is not normal, correct?

I can try and dial the gas back, that would seem to be the only option left to try. Unfortunately I'm into it about 700 rounds, so if I have to let it clearance itself, it's going to take a bit of time.

Does this help?



It's the same on the other side. Sorry for the pic, not a good camera. Under "normal" circumstances, is the bolt supposed to go back that far in the first place?

It's not light contact, seems that I can feel it when retracting the charging handle, and it sure feels like recoil is more harsh. I didn't make any attempt to check if it actually is, but the plastic at the back of the buffer shows no signs of impacting the extension. Obviously since it's cutting aluminum away, it's not just some wobble.

Due to the GII's re-designed ejection port, not sure if the measurement would be comparable. As it is now, the bolt retracts to about 1/8" past the bolt catch, which I'm guessing is about where it needs to be.

The tube is actually pretty thick there, it doesn't appear that it's going to cause any structural issues.

I may even have to carefully remove some material there myself. I've been playing with different loads, so I can probably dial the gas back more, maybe that will help. Yes, it's not something I caused and shouldn't have to attempt to fix, but DPMS customer service (as one recent experience was reported) seems like a black hole. Send the rifle in, you hear nothing. And it could be ~6 months before you get it back.

Here are a couple of pictures I took, they tell you anything?





Minimal movement between the upper and lower. There is some of course, but much less than I've seen on other rifles that still function fine.

Looks like the buffer tube is threaded on to far.  Try backing out the buffer tube one turn.

Either that or maybe not square?  Looks like it is just impacting the lower portion of the tube.  Have you checked to see if the tube face is square?  Kinda hard to see with those pics.

They have evidently designed a clearance issue into the rifle. I would contact them to see what they will do about it. I think its one of those things that will wear in and not be a problem, but its definitely not right. It could be a slight dimensional problem with the center of the extension ring on the lower, with the center of the ring maybe .005" too high. 'Ramping' the carrier guide rails at the rear might stop it from rubbing but I wouldn't do that unless they won't fix it, which I'm sure they will. This should have created quite a 'rub' when slowly hand-cycling before firing - did you not notice anything?

I am pretty manly, so not surprising I didn't/don't feel that aluminum getting in the way. lol

No, never really noticed it before. That does seem suspicious, taking the gun apart it appears pretty clear that even just charging the rifle, the bolt carrier comes back far enough to impact the tube, so I don't know why only now am I figuring this out.

Honestly it doesn't seem like it has done it in the past, or I would have noticed the aluminum slivers earlier one would think. Then again, I've also taken my time working up loads, starting very low, and maybe just now I'm loading them hot enough to really thrust the carrier back into the tube hard?

I know the consensus is send the gun back, that is going to suck. :( But I agree, cutting/grinding on the gun probably isn't going to have them feeling any too generous to fix it.

I have to agree, it looks like misalignment (vertically) of receiver and extension tube. With all the mishmash of parts I've used, I've yet to encounter that. Dang, that thing must be WAY off.

Any update?

No update, slowly contemplating in my head how anything I've done could have caused this.

I don't really see how, I've not touched the extension, bolt carrier, etc., just replaced the hand guard and buttstock, but I don't want to send it off to hear back that something I did is the issue.

It really is the time to start digging into this though, if six months is the norm, I'd like it back before summer.

OP,
This stuff happens all the time.  Just call DPMS and let them help you with a return label.
Have a great Thanksgiving!

Are you sure that is what is happening? Did you try to close the lower without the carrier pushed in all the way and make those markings with the bottom of the carrier?

The guide rails (whatever the proper term is) that impact are at least 3" forward of the tail of the carrier, there is no way for those to make contact by having the tail of the carrier hang out trying to reassemble the rifle. The slivers of aluminum are consistently found where the lower guide rails end, on the underside, in the relief cut.

I had no question what was making the marks, only why.

I did not even read the post and problem correctly. Thought you were talking about the marks at the top of the lower.
My cousin has one of the Recons. I would guess if your stock and stock parts are factory his will have the same marks as yours. On a standard At the rails never enter the tube. I will check how far the carrier rails go back into his lower stock tube next time I see him. Might ask others to look at theirs in the DPMS forum if you have not asked yet.

Good point. How is the carrier moving that far back? The other question is how it your buffer detent surviving if the carrier is moving that far back (carrier is not cut to clear detent that far back)?  Is the carrier key slamming into the CH? As J3 pointed out, the carrier should bottom out prior to the rails entering the RE tube. You're not running some kind of "short" buffer are you? Or a longer than carbine RE? Something is messed up there, and if it's stock... I'd send it in ASAP.

Billy what's his name (I actually like the guy, at least from his youtube videos) did one of James Yeagers classes and as I recall, put ~2000rounds through one. Of course, IIRC he was working for Remington/Freedom Group at the time, but I'll just take the series at face value.

I've got 7-800 on this rifle without evidence of issue there, but I know that's not indicative of long service life. DPMS did modify the bolt after some months, but from what I could see, didn't appear to be related to lug strength. I suspect, but could be wrong, that they removed potential fracture points in the design by not making square cuts at the base of the lugs. I can't recall if they advertise the bolt being a harder material than the LR-series bolts.

Interesting that article you linked...the receiver being 5/8" longer (according to DPMS) over the AR15, seems to be very close to the distance gained with the shortened gas carrier key over the LR-series bolt carrier/gas key.

I am almost 100% certain the view from the side of both carriers in that article (I'll just add that pic below), show a "second generation" GII bolt. At full size you can see to the rear of where the material between the bolt lug is cut away, there is a tool mark from the cutter.



This is how all the second generation bolts appear. Plus, the cut around the circumference of the bolt just behind the lugs is much larger on the early bolts. The main functional difference appears to be that they made the firing pin tunnel the proper diameter, so everyone doesn't end up with the "first generation bolt" cratered primers.

But shockingly (being dramatic here, somewhat), and directly in line with what you mentioned before, you can clearly see that  "guide rail" lower rear edge has been angled, exactly where mine hits. Sure enough, my first generation bolt (and now there is evidence both the bolt and carriers are different) is not angled in the same place. The lower edge is a square, sharp cut.

This kind of pisses me off. I emailed DPMS whenever we first started to see the second generation bolt, to ask when and what all was changed when the bolt manufacturing was obviously modified, and I didn't receive an answer. Perhaps this is why.

I'd also like to measure the depth of the cutout on the carrier for the dust cover door detent on the second generation bolt carrier. Mine doesn't open unless the action is cycled viciously, because the detent barely hits the carrier The cut in that picture appears much deeper, but that's pretty tough to tell with certainty. That would have been something else to fix, although not sure how, without creating an all-new dust cover detent design.

Talked to my cousin this morning and he says his stock tube has the same banged up spots as yours. He bought his when they first came out and has the earlier bolt in it.

Not sure if anyone cares for updates, but I sent DPMS an email yesterday with a picture and comments on that problem, along with a couple other minor issues I have with the gun. Nothing yet.

I took a higher quality picture of the problem, it seems to make the tube in general look worse than it is, at the same time giving little indication of how deep the scoring is from the bolt carrier hitting it.

I'll keep updating, just to keep the thread alive.

Received a response from DPMS, asked for address and SN, "so I can set you up for a repair."

BTW, I have no qualms about posting my serial number, its AA001777. I'm guessing that is a pretty early gun based on the AA and 1777, but haven't found anyone else willing to share even part of their serial number to know for sure.

Would be nice for buyers to know that serial numbers below XXXXXXXX have the "gen 1" bolt/carrier setup.

Rifle shipped to Ahlman's the 22nd. Haven't heard anything back yet, but I assume the holidays are going to slow things down a bit.

We'll see!

Got a call from Ahlman's last week, said they got the gun working(? I'm sure they meant got it to stop hitting the extension tube) and were going to work on a reprofile for me, so should see it in the not too distant future. Not going to be able to get to shoot it for some time, but I'll look it over very well upon receipt.

I also own a DPMS Gen 2 recon. Mine has wear in the same places as yours but not as pronounced. My carrier rails are tapered at the rear where they enter the tube. However, I only have a few hundred rounds through mine. I'm not going to worry about it unless it starts eating into the receiver threads and then I'll just replace the buffer tube. Keep us posted!

I only put about 100 rounds through my GII before making some modifications.  I cleaned it 3 times during that period and never noticed pieces of aluminum or impact marks in the tube like yours.  I just got mine (new) in November.  My serial number is EHO15XXX (almost 16000).

I replaced my carbine type buffer tube with a fixed stock tube and A1 stock (I like those A1 stocks, they just fit me very well).  I still haven't gotten to the range to fire it since the modifications.

Hope they take care of it for you.

Interesting serial number. Nowhere near what mine is, I wouldn't have thought a deviation would have happened that significant. Does your gun's ejection port cover open every time you cycle the bolt, even slowly? Wondering if some changes happened to the receivers that necessitated a serial number sequence change to clearly indicate.

I don't expect the wear to completely disappear, but with smoothed edges it won't gouge large slivers off at a time. Not sure how that could be solved without a complete redesign. They said they "made my gun work", so assuming I get the same one back, I'll try and see what was changed and/or modified and report back when I get it.

To keep the thread alive, as I'd like to post a resolution, if it happens...

Called Ahlmans again as I'd not heard back. Not in a hurry, and they are going to do some barrel work on it for me at the same time, so sure enough, they said it would be a few weeks before the barrel work was done.

Got the call today, $250 to do the barrel reprofile, it's complete, got a tracking number for the return shipment. :)

Got the rifle back. Very happy with Ahlman's turnaround time, work and communication. I told them I was in no hurry, I figure for all the work they had to do, it was still a fairly quick turnaround. No issues getting response to email or answering the phone.

Complete BCG replaced with the "new" version. I've always had cratered primers, will be interesting to compare primers from the new bolt to the old ones.

Buffer tube replaced.

Ejection port cover replaced. Didn't work right before (wouldn't open unless the bolt carrier was moving quickly), and no idea how that was fixed, but it was.

AAC 51T and Gas block replaced, not sure why.

Was test-fired.

Barrel reprofile and fluting look great.

Rifle sans scope/rings, BUIS, brake is at 6lbs 10oz. I used that figure to compare to bolt guns that are advertised "bare".

Rifle as pictured is 8lbs 2oz:


Still remains for me to shoot it, but I suspect I'll see much less from the bolt carrier impacting the buffer tube now. :)