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Posted: 6/23/2012 3:01:04 PM EDT
| I have just succumbed to the urge to build an AR15, so this is my very first––I've never even fired one. I bought a DPMS Sportical upper, a flat-top carbine length (16") chrome-moly barrel. I am just about to undertake the assembly of the lower, but I've been fiddling with the upper, a bit––taking it apart and putting it back together, etc. I have noticed that, when drawing the bolt back, there is a scree-e-e-e sound of metal ridges on metal ridges. And looking at the bolt, it clearly has annular tool marks on it. And likewise, the upper (aluminum, right?) also has annular tool marks inside it that I can feel with my fingernail. I have no doubt that it is these tool marks that account for the awful screeching sound I hear. Granted, the parts are currently bone dry (no lube whatsoever), but it just seems as though this is just asking for a wear problem. Am I over-reacting? Can any of you experienced AR folks tell me if my expectations for fit and finish are unrealistic? What would you advise? |
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As stated a picture would help. The carrier actually only contacts the upper receiver at a couple points.
Some toolmarks might be normal and ok, but could easily be your issue although it would be rare and probably a case of a bad one sliding through QC. Other places where you are more likely to see the cause of this issue would be where the charging handle contacts the upper or secondly ridges on the ID of your receiver extension. Or this could just be an issue with cycling it dry. Feel the ID of the extension. Is it smooth or ridged? Check how the charging handle is wearing in the receiver. Any excessive wear spots? Throw some lube on there... do you still get the grinding sounds? |
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Quoted:
Can you post a pic.......it Shouldn't make noises like that ...it should slide free and smoothly If you have something that is scraping or binding it has the potential to cause malfunctions. Hey, thanks for all the replies to my post! I thought I would get notified by email if anybody responded––I guess not. Good suggestions for getting pictures. I don't have a camera with macro lens, so I used my flatbed scanner on hi-res. I've never tried to post a picture, so let's see how this goes: https://dl.dropbox.com/u/17684270/DPMS%20carrier%20striations%2027Jun12.jpg OK, I thought I would have been able to upload a picture to my reply, but that didn't work. (How does one provide a URL to a photo that resides on a local hard drive on my computer? I don't have a web server...or even a web page of my own.) So check the Dropbox link above for my picture. It just seems as though the lathe that was turning the carrier parts was set to a coarse finish, or else there were follow-up finishing steps omitted. The inside of the upper receiver seems to have a little bit better finish, but it is not really smooth, either. Oh, and for all of you that mentioned wear, keep in mind that I have never fired a single round through this gun, yet. And as far as the buffer spring––the carrier makes the sound I'm talking about when completely removed from the lower receiver. Have I got an exceptionally poorly machined carrier group on my hands? |
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I just pulled the bolt carrier from 5 of the AR's I have here at the house........(all toolcraft) and it sure looks like someone skipped a step or two on quality control......WHERE did you get that corn cob? That definitely is a rough looking carrier. If they won't make it good......let me know.....
Edit: Just saw it was a DPMS.....good people should swap it out no problem....send them the pic you posted..... |
| Thanks for all the advice! I had emailed DPMS, twice, but got no reply, yet. But with the confirmation you all supplied that this finish is unacceptable, I called DPMS and am returning it. I'll post after I get it back and let you know what DPMS did for me about it. |
| DPMS has replaced my "corncob" carrier, and the new one does look much better. I was hoping for some kind of explanation regarding my repair, but there was nothing more than some terse remarks on the paperwork like "customer was concerned about the finish on the carrier"––sounded a bit dismissive and elusive, to me. But they did replace it, as requested, so I've got no complaints with DPMS. |
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The carrier shouldn't really rub the inside of the upper reciever.
The only parts that should possibly be making contact consistently are the gas key and the bolt cam pin. Everything else should barely touch as the carrier cycles. It might've worked fine as is, but DPMS should've shown a little more pride in workmanship and sent that one out to Blackthorne like they do with the rest of their rejects. 
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