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Posted: 1/29/2004 4:16:22 AM EDT
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I just recently built an AR-15 and i'm having problems with ejection. The problem started with firing the round without ejecting the brass. I checked the gas rings and they were OK. I checked the gas tube and the holes match and there are no obstructions. I tried a different buffer tube and spring and that didn't have any effect. The bolt is brand new and the extractor is fine. I used factory ammunition to eliminate any failures that may be caused by reloads. I tried different magazines and it still doesn't work. I then tried using a friends M-16 bolt carrier in an experiment to see if the weight of the carrier made a difference. With the M-16 carrier it would cycle for 3-4 rounds and then fail to eject. What am I missing????? |
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Need more details on "ejection problem". Is the round coming out of the chamber? All the way, half way? Or not being kicked out? Run this test. WD40 the chamber, WD40 the entire bolt assy, grease the gas rings well, grease the bolt lugs, WD40 the outside of the carrier, grease the outside of the carrier key well. Put one round into a mag, chamber, and fire. If the bolt does not lock back, you have a gas problem. If the case comes out more than half way, WD40 chamber again, chamber another round, take out the mag and fire. If still only more than half, it's a gas problem; if less than half, it's a chamber problem. |
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Do not spray lube into the chamber, that will only lead to more extraction problems. There's a troubleshooting checklist in the Troubleshooting Forum. [url]http://ar15.com/forums/announcement.html?b=3&f=66&id=184[/url] Was the HS checked on the barrel before you fired it? Did you try a different bolt or just the other carrier? |
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No, I don't have a way to check the headspace. That was another of my concerns. I asked about headspacing once before and the replies I got was to tighten it as tight as it would go by using a handheld wrench and it would be OK. To answer the other question about the bolt, We just swapped the bolt and carrier together as a unit. We tried it and it fired a few rounds and then failed to eject leaving the extracted case just above the magazine in the magazine well. It was then cleared and reloaded and tried again and did the same thing. |
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Quoted: I asked about headspacing once before and the replies I got was to tighten it as tight as it would go by using a handheld wrench and it would be OK. The barrel nut has nothing to do with headspace. No, I don't have a way to check the headspace. That was another of my concerns. You have ammo, right? If a factory round chambers easily, headspace is not to short. Try to chamber one by hand by pushing the bolt carrier forward with your thumb. Normally I'd say the gas tube is upside-down, but you said you checked that. I think your problem is the barrel - a rough or tight chamber. This sounds just like the problems people were having several years ago with Olympic "Match" barrels. Who made your barrel? Is it chrome-lined? |
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Quoted: We just swapped the bolt and carrier together as a unit. The problem is most likely in the barrel then, either the chamber or the gas port. What make of barrel is it? Many loaded factory rounds are smaller than the GO HS dimension. Cases are built to a "max cartridge" limit, the "max cartridge" for the 5.56 is roughly GI HS. For example, one manufacturer specifies a range of 1.4666 to 1.4606 for the HS dimension of their .223. In comparison, the GI GO HS dim is 1.4646" + 0.0002". The range varies from maker to maker and lot to lot. Another concern is that the HS dim on the case is not controlled, the manufacturers build cases based on diameter and distance. Given the 5.56 case, they are concerned with the diameter of the shoulder and its distance from the base and the diameter of the neck and its distance from the base. Given there is a relation between the two locations the HS dimension [b]should[/b] fall in it's proper location. There is even a small bit of slack in the chamber, bolt, barrel extension relationship. A tight HS/large cartridge mix can work by using all of this slack. When a round is chambered in a barrel with short HS there will be insufficient room for the brass to expand when the cartridge is fired. This leads to increased chamber pressure and failures to extract. Checking with a cartridge beats not checking at all but you don't know what size the cartridge is or where on the shoulder it stopped. None of the above is a concern with gages as that's what they were designed for. And yes, I have set HS with a cartridge when necessary. Are .300 Whisper gages available yet? |
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Sounds to me like your chamber is too tight. My DPMS had the exact same problem. There are only two places you could be getting a gas leak. One is the gasblock itself. The other is through the carrier. And you tried out a new carrier so that means you are either losing gas at the block, or more likely the chamber is too tight, thus even with 100% gas pressure, it takes too much energy to pull the expanded case out of the chamber because it is wedged in there so tight. I had to send mine back to DPMS and they opened it up a little bit and now it works flawlessly. And there is no way someone could have their gastube upside down, it would never line up through the barrel nut and into the receiver. |
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Quoted: And there is no way someone could have their gastube upside down, Yeah, you would think that given the bends in the gas tube it would be impossible for someone to install one upside down. We just had a report of another one in the Tshooting forum last week. Happens about once every three months here. It can happen. [url]http://ar15.com/forums/topic.html?b=3&f=66&t=179570[/url] |
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My barrel was bought from Fulton Armory. It's the 20" barrel that was standard on the AR-15/M-16 when they first came out. I wanted an older style AR like the one I used to carry when I was in the Air Force. (Triangular Handguards, No forward assist, three prong flash hider etc.) |
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I return it to Fulton, don't they have a board here too? If it's a former GI barrel then HS shouldn't be a problem since GI barrels are HSed long from the start. I'd replace the extractor and spring with a known good one and re test. Check to see in which direction the brass is leaving the ejection port. Does the bolt lock open on the last round out of the mag? What size is the gas port? |
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