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Posted: 5/5/2011 12:45:21 PM EDT
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okay so I picked up a used DPMS 308LR. and tried to test fire today and much to my surprise, it no go bang!
It was having problems feeding rounds from a PMAG up into the chamber and leaving scares on the rounds. Sorry for the crappy cell phone pics 
feed ramps- 
scars on federal rounds- 
And the bolt seemed a little funny to me. When it would feed rounds it wouldnt fire. The cam pin seems "backwards" to me. Shouldn't it be turned 90 degrees from were itis right now? and the firing pin would not go into the bolt in order to strike the primer unless I manually pushed it down.(when the bcg was out of the rifle of course). cam pin on bc- 
cam pin out- 
firing pin- 
Any suggestions? Thanks for your help!! |
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1. The cam pin is right 2. AR's don't like ammo with long exposed soft lead tips 3. I wasn't aware that DPMS .308's had firing pin springs, mine doesn't 4. Check to make sure you're properly installing the firing pin, and that the firing pin retainer is installed after the firing pin is fully inserted. you may be slamming the firing pin flange into the retainer if the firing pin isn't installed all the way before inserting the retainer. |
| Armalite BCG's have springs on the firing pin, and apparently so do some DPMS. Do not remove it. It's purpose for being there is the increased kinetic energy transferred in a .308 AR system when the BCG moves forward. .308 AR's have much heavier BCG's, firing pins, and heavier buffer springs. Not an issue in the lighter weight AR15 action, but with a .308 AR it could impact the primer hard enough to touch it off. |
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Somebody installed an AR-10 firing pin instead of an LR-308 firing pin. They are different.
AR-10: http://www.armalite.com/ItemForm.aspx?item=EA6060 LR-308: http://dpmsinc.com/store/products/?prod=4812 As for the feed problems, give it a good cleaning first. If you haven't, try underloading the magazine. If you have one available, use a factory magazine as well. The firing pin is the reason for the failure to fire, but it may not necessarily be the reason for the feeding problems. |
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Somebody installed an AR-10 firing pin instead of an LR-308 firing pin. They are different. AR-10: http://www.armalite.com/ItemForm.aspx?item=EA6060 LR-308: http://dpmsinc.com/store/products/?prod=4812 As for the feed problems, give it a good cleaning first. If you haven't, try underloading the magazine. If you have one available, use a factory magazine as well. The firing pin is the reason for the failure to fire, but it may not necessarily be the reason for the feeding problems. I'm not sure as to the DPMS's but the LT-OBR has the same springs on the firing pin. I've heard of scattered instances where prior 308 ARs, such as the older SR-25's. Some now use the spring as a preventative measure. Firing pins without that spring sometimes have enough inertia to cause a double shot. |
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Somebody installed an AR-10 firing pin instead of an LR-308 firing pin. They are different. AR-10: http://www.armalite.com/ItemForm.aspx?item=EA6060 LR-308: http://dpmsinc.com/store/products/?prod=4812 As for the feed problems, give it a good cleaning first. If you haven't, try underloading the magazine. If you have one available, use a factory magazine as well. The firing pin is the reason for the failure to fire, but it may not necessarily be the reason for the feeding problems. I'm not sure as to the DPMS's but the LT-OBR has the same springs on the firing pin. I've heard of scattered instances where prior 308 ARs, such as the older SR-25's. Some now use the spring as a preventative measure. Firing pins without that spring sometimes have enough inertia to cause a double shot. Yeah, as far as I know springs are included as a preventative measure against slam firing. I've never had it happen to me personally, though I have had dimpled primers before. The AR-10 is designed for a firing pin with a spring, while the LR-308 (and the AR-15 for that matter) are not. I assume they are designed that way for a reason, and while the dimensions are close enough that the AR-10 firing pin will fit (it might even be an entire BCG for all I know) it looks to me that the two firing pins do not share the same profile. I know other systems use springs but I don't think they are interchangeable in most cases. I wonder if he's having light primer strikes. The spring would explain that. From what I've seen and experienced pulling a round out of the magazine is more than enough to slow down the bolt and prevent slam firing. The spring in the LR-308 might go beyond that and prevent it from striking the primer hard enough. |
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Somebody installed an AR-10 firing pin instead of an LR-308 firing pin. They are different. AR-10: http://www.armalite.com/ItemForm.aspx?item=EA6060 LR-308: http://dpmsinc.com/store/products/?prod=4812 As for the feed problems, give it a good cleaning first. If you haven't, try underloading the magazine. If you have one available, use a factory magazine as well. The firing pin is the reason for the failure to fire, but it may not necessarily be the reason for the feeding problems. I'm not sure as to the DPMS's but the LT-OBR has the same springs on the firing pin. I've heard of scattered instances where prior 308 ARs, such as the older SR-25's. Some now use the spring as a preventative measure. Firing pins without that spring sometimes have enough inertia to cause a double shot. Yeah, as far as I know springs are included as a preventative measure against slam firing. I've never had it happen to me personally, though I have had dimpled primers before. The AR-10 is designed for a firing pin with a spring, while the LR-308 (and the AR-15 for that matter) are not. I assume they are designed that way for a reason, and while the dimensions are close enough that the AR-10 firing pin will fit (it might even be an entire BCG for all I know) it looks to me that the two firing pins do not share the same profile. I know other systems use springs but I don't think they are interchangeable in most cases. I wonder if he's having light primer strikes. The spring would explain that. From what I've seen and experienced pulling a round out of the magazine is more than enough to slow down the bolt and prevent slam firing. The spring in the LR-308 might go beyond that and prevent it from striking the primer hard enough. No light primer strikes due to the primer not being struck at all. |
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sorry to say it, but it looks like you have a frankin gun,
if that rifle was built at DPMS it should have the M4 feed ramps, and they dont make a chromed .308 bolt. plus as has already been said that is not a DPMS firing pin. i'm betting the lower SSN# has a "K" in it, meaning it was not sold as a complete rifle. looks like maybe someone put an armalite bbl into a DPMS upper for some reason? ETA: looked closer at your BC, and it is not a DPMS either. on the DPMS, the radius on the sides below the cam pin is made up of several flat areas instead of a single curve. |
Heres the bcg-
heres the bolt itself- 
Okay so if this is an armalite upper on a dpms lower will it work? Whats it going to cost me to make it right? IF (and its a big if because I bought it off of this site from another team member and don't want to hurt anybodies reputation with out just cause) Do you think it is right to sell this rifle as a complete functioning DPMS rifle? |
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if the guy billed it as a factory DPMS rifle, i'd be pissed as hell. used or not.
its prolly still a DPMS upper, they just filled it with armalite(or other) parts. nothing on that BCG is DPMS. dont know how many rounds he told you he had through it, but it looks like he put enough through to break an extractor. but yea, this is NOT a factory rifle. and if it is a used rifle that was supposed to be functioning a the time of sale, then you should be able to just put a mag in and shoot. |
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if the guy billed it as a factory DPMS rifle, i'd be pissed as hell. used or not. its prolly still a DPMS upper, they just filled it with armalite(or other) parts. nothing on that BCG is DPMS. dont know how many rounds he told you he had through it, but it looks like he put enough through to break an extractor. but yea, this is NOT a factory rifle. and if it is a used rifle that was supposed to be functioning a the time of sale, then you should be able to just put a mag in and shoot. Heres the sale thread |
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I can't identify it exactly, but I can say for sure that isn't a DPMS bolt carrier. It might be a Fulton, but I can't say that for sure either. It has some features of an AR-10 bolt carrier and some features of a Titan bolt carrier. Then again, what do I know?
If I were you, I would identify all of the parts you have (by manufacturer if possible) and see what has and has not been modified. As to whether it's right to sell this as a functioning rifle, absolutely not. For one, the damn thing doesn't fire. That's like selling a car that won't start and saying it runs well. Second, it's obviously, as others have a said, a Frankenstein rifle - at best, if it shot it would be considered a "custom" 308. It's not a DPMS and it's not an AR-10. |
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if the guy billed it as a factory DPMS rifle, i'd be pissed as hell. used or not. its prolly still a DPMS upper, they just filled it with armalite(or other) parts. nothing on that BCG is DPMS. dont know how many rounds he told you he had through it, but it looks like he put enough through to break an extractor. but yea, this is NOT a factory rifle. and if it is a used rifle that was supposed to be functioning a the time of sale, then you should be able to just put a mag in and shoot. Heres the sale thread If he's telling the truth, you can't blame him. He didn't say he shot it and he didn't make it sound like he knew much of anything about it. In hindsight, there's a reason he got it in trade - the thing won't shoot. Maybe he knew that and maybe he didn't. If he did then selling it to you was incredibly dishonest, but there's no way to know what, if anything, he knew about the condition of the rifle. In the worst case, you can identify as many parts as possible and just part the rifle out. With any luck you'll recover your investment. Hopefully what's wrong is fairly minor and it won't come to that. |
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to make it work you will have to figger out if the bbl ext and BCG are DPMS or Armalite pattern. if the bbl ext is a DPMS pattern then you should just need to order a DPMS BCG and bring it to an AR gunsmith to be headspaced. Any easy way to tell, rather than markings on the piece. Because there's nothing on that BCG as far as manf. |
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Does the FP even protrude from the bolt face when pushed as far forward as it will go? The differing front shapes of the two pin styles suggest the armalite wouldn't protrude from the face of a DPMS style bolt.
A possible cheap test would be a new DPMS pin. That may be all you need to get the rig to fire. |
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Does the FP even protrude from the bolt face when pushed as far forward as it will go? The differing front shapes of the two pin styles suggest the armalite wouldn't protrude from the face of a DPMS style bolt. A possible cheap test would be a new DPMS pin. That may be all you need to get the rig to fire. Agreed but check the headspace first don't take the risk. If it doesn't pass the headspace gauge test then I would have to say your best bet might be to just pick up a barrel and a new BCG. I know that that sounds kind of sucky but for a little over $400 you could get the rifle running like new and do so safely. Although, J75player, do you know what kind of upper that is? I've never seen one before but I figure with your background if DPMS ever made something like that you would know. Assuming the upper receiver is gtg I'd be willing to put it together for you if you don't have the tools, I know I live in OH but you ship it to me I'd ship it back, the shipping would be a lot less than the tools needed. |
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to make it work you will have to figger out if the bbl ext and BCG are DPMS or Armalite pattern. if the bbl ext is a DPMS pattern then you should just need to order a DPMS BCG and bring it to an AR gunsmith to be headspaced. Any easy way to tell, rather than markings on the piece. Because there's nothing on that BCG as far as manf. well, i worked for DPMS so i know thier stuff really well, Armalites not so much. so i am not exactly sure how to tell the diff between the two. I belive that the an arma botl will lock into a DPMS extension, but that you will have very tight headspace. i do konw for sure that the gas tube on the arma's are a 1/4 inch longer. i think your best bet is to either find a member near by (home town forum) that knows both platforms well. or goto a local gunsmith and have them look it over, i doubt they will charge you anything to look at it and tell you if its arma or DPMS. (oh, and it is a slab side DPMS upper receiver) |
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The upper is a Panther LR-308B Rifle, it's extruded, no forward assist and no duct cover.
The BCG is not ArmaLite. Does the bolt have three gas rings (DPMS) or a single McFarland ring(AR)? For testing feeding you need some FMJ ammo, those lead nose bullets are a problem for doing any kind of reliability testing at this point. Do you have more than one mag? Clean everything as well as you can. Leave the firing pin out of the bolt and do some feed testing with some good ammo. It could be as simple as just the wrong firing pin and soft nose bullets. |
| The three BCGs in my DPMS rifles (made several years apart) are interchangeable. It was stated earlier in the thread that a "K" in the serial number on the lower indicated that it was originally not a complete factory rifle. In the pictures shown in the "for sale" thread, it appears that the serial number ends with a "K". Would that not indicate a "custom" rifle rather than a complete factory rifle? Look back through this thread for the "for sale" thread and check the photos, notably the one showing the serial number. |
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