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Posted: 8/24/2013 6:45:53 PM EDT
Ok so I have a new DD m4v7. I am no ar15 expert so bear with me. I have about 200 rounds through it & I've been having feeding issues from the beginning. While firing and when loading a new round from a full mag it will pick up the round but not chamber it fully.
I have tried multiple ammo types as well as different mag types. I've also taken the bolt from my rifle and put it in a buddies rifle and his began to malfunction in the same way. His bolt in my rifle ran flawlessly . So common sense tells me it's an issue with the bolt but maybe I'm missing something. I plan on calling DD Monday morning but I was hoping to gain some insight. Any help is appreciated. |
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Check the tension on the ejector, is it going in and out without binding?
Also check the tension on the extractor. Does the lip of the extractor, the part that grips the case rim look correct? Does the bolt go in and out of the bolt carrier with out too much resistance. Does the bolt face look like it has the proper dimensions, ie can you place a case head under the extractor, and rotate it down into be bolt head compressing the ejector? |
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Check the tension on the ejector, is it going in and out without binding? Also check the tension on the extractor. Does the lip of the extractor, the part that grips the case rim look correct? Does the bolt go in and out of the bolt carrier with out too much resistance. Does the bolt face look like it has the proper dimensions, ie can you place a case head under the extractor, and rotate it down into be bolt head compressing the ejector? Ok so I cleaned and lubed & it still malfunctions at the same rate. The bolt face has the proper dimensions as far as I can tell with the method you suggested . There is one thing I've noticed , when it malfunctions the round is " canted" to the side and not under the lip of the extractor 
Does this mean an issue with the extractor? The tension of the ejector seems fine . This is the best pic I could get of the bolt face 
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| In your situation I would consider sending it in for warranty work but I probably wouldnt do it. I may try to change the extractor and spring. More than likely I'd just buy a BCM bcg. If that did not correct the issue I'd send it in for repair and still be glad I had a spare bcg. |
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OP, your issue is not being caused by the ejector or extractor. The round itself would still fully enter the chamber regardless, with the bolt being stopped while engaging it instead. The extractor does not attempt to slip over the case rim until the round is completely in the chamber. I am assuming that this is a DI rifle in which the chamber and BCG have both been properly cleaned and lubricated. Please correct me if this is not the case.
From the position of where the BCG rests after stoppage occurs in your photos, it may be experiencing binding between the carrier key and gas tube. Does the BCG manually cycle without issues on an empty chamber? If so, remove the carrier and test fit a round into the chamber to check for too tight of a fit. The round should seat easily and drop free under its own weight when tilted back. Check for any anomalies or damage to the key and tube as well. When the jam occurs, is the cartridge able to still move freely and enter the chamber if you tilt the muzzle downwards? Even though both of these tests may pass, it is still possible that binding is occurring due to either the BCG or upper receiver carrier bore being on the outer end of tolerances, with an excessive amount of fit between them. When the BCG is passing over the rounds in a loaded magazine, it is possible that the upward tension may be pushing the carrier up enough as to cause binding. You can test this by removing the magazine, locking back the bolt, placing a round into the chamber and then pushing the bolt release, allowing the carrier to slam home. It should lockup without any issues. Please post your results of these tests. ETA: Also, as others have mentioned, your BCG appears to show a great deal of wear. If the gas rings are excessively worn, you might experience bolt binding due to the cam pin dragging against the channel. |
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OP, your issue is not being caused by the ejector or extractor. The round itself would still fully enter the chamber regardless, with the bolt being stopped while engaging it instead. The extractor does not attempt to slip over the case rim until the round is completely in the chamber. I am assuming that this is a DI rifle in which the chamber and BCG have both been properly cleaned and lubricated. Please correct me if this is not the case. From the position of where the BCG rests after stoppage occurs in your photos, it may be experiencing binding between the carrier key and gas tube. Does the BCG manually cycle without issues on an empty chamber? If so, remove the carrier and test fit a round into the chamber to check for too tight of a fit. The round should seat easily and drop free under its own weight when tilted back. Check for any anomalies or damage to the key and tube as well. Even though both of these tests may pass, it is still possible that binding is occurring due to either the BCG or upper receiver carrier bore being on the outer end of tolerances, with an excessive amount of fit between them. When the BCG is passing over the rounds in a loaded magazine, it is possible that the upward tension may be pushing the carrier up enough as to cause binding. You can test this by removing the magazine, locking back the bolt, placing a round into the chamber and then pushing the bolt release, allowing the carrier to slam home. It should lockup without any issues. Please post your results of these tests. ETA: Also, as others have mentioned, your BCG appears to show a great deal of wear. If the gas rings are excessively worn, you might experience bolt binding due to the cam pin dragging against the channel. With no round in the chamber the bolt slams home 100% of the time. I dropped A round in the barrel and it fit snug . Upon tilting the gun back the round did not fall out on its own . A firm tap on the butt stock dislodged the round. Also when a round is placed in the barrel I released to bolt with no mag attached and it slammed home fine. Like I said before the rifle has 200 or less rounds through it so I'm not sure why it would show excessive wear . |
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With no round in the chamber the bolt slams home 100% of the time. I dropped A round in the barrel and it fit snug . Upon tilting the gun back the round did not fall out on its own . A firm tap on the butt stock dislodged the round. Also when a round is placed in the barrel I released to bolt with no mag attached and it slammed home fine. Like I said before the rifle has 200 or less rounds through it so I'm not sure why it would show excessive wear . Please check the other things I listed as well...ie;, gas rings etc.. and look for any gouging or rough spots in the cam pin channel to rule out bolt binding. Also, make sure the chamber mouth is tapered. Last, test the BCG fit to the upper. If it is too loose, the scenario I mentioned about the loaded magazine pushing the BCG up enough to bind it on the key may be the cause. You can test this by removing the upper from the lower and use your finger to push up against the bottom of the BCG (from the area directly behind the bolt) while slowly moving it into battery with the other hand. Does it bind against the tube? ETA: Make sure to no longer let the carrier slam on an empty chamber, this can eventually displace metal on both the barrel extension as well as the carrier and the front of the bolt lugs, including the firing pin hole. That is the most likely cause of the wear we are seeing in the photos. |
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Is it me or does the end of that extractor look like it's not sticking out far enough to be lined up with the bolt face? With it being so far down like that, does the rim of the casing even fit under the claw? http://bisonarmory.com/product_images/uploaded_images/bolt-stag-new2.jpg was just looking at that myself, looks about 1/8" short like the lip is sitting damn near on the bolt face. I just looked at 4 bolts 2 of which are in excess of 5000 rds. and none look like that no matter what angle I look at the face from and with glare from bright light on it. op, check to see if you can slip a case rim under that extractor by hand while it out of the upper. |
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I think most of the wear on the bolt face ( around the extractor)is from slamming into the round at the weird angle as shown in the above pics.Talked with a guy at DD , he said it sounds like an issue with the bolt being out of spec. I will be shipping it in for inspection and repair .
Eta : yes I can get a round to sit flush on the bolt face under the extractor lip but when it malfunctions the case isn't sitting under the lip. So the full force of the bolt closing is ramming the extractor into the case causing the wear. You can see in this picture how the round is slanted to the side of the extractor on a malfunction.
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Can you take a picture of the bolt in the same angle as the previous image I posted? Wondering if the extractor is out of spec or if the hole for the extractor pin is off. I guess even a reputable company like DD can have an oops moment as well...
If you want to check for your own knowledge, swap out the extractor with another one and see how it fits. |
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Just got an Update from DD
"Just a quick note to let you know that I received your rifle today. Our armorers were able to take a look at it and discovered the bolt carrier group was indeed out of specifications. We replaced the BCG for you. We were, unfortunately, unable to test fire it today due to time restraints. I will have all of the function tests performed when we return on Tuesday then ship it out to you Tuesday afternoon. Have a great weekend and enjoy your holiday!" Eta they've been great this far as far as customer service goes |
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Well, glad they replaced the BCG. I keep learning from these posts… even if a solution doesn't apply, it drills it into us what can cause what symptoms, etc. Well said. ARF.com "Troubleshooting" is something I do right after the morning crossword puzzles, for the intellectual value of the problem-solving. As a sport, it's a lot more about thinking than shooting..... 
mully PS: it's not a sport if it can't kill you. 
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