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Posted: 3/13/2006 4:34:48 PM EDT
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Hi guys: I have a dmps 24" ss bull barrel that I am having a FTF problem on any ammo and mag. I have gone threw the trouble shooting list and found the gas tube worn out on the end and the gas block misaligned to the barrel port. I relpaced the gas tube and fixed the alignment. But still having the problem. I did the one round test many times and all locked back ever time. I have used different B/C/CH and different lowers, no change. Sometime the shell eject fine but the next round does not feed and good percentage of the time it stove pipes. Last time at the range when I pulled the mag to clear the mess the next round in the mag the copper had gone from shinney to dull purple in color like it had been heated. I do not know if that is normal. The barrel shoots great but before I replace the upper receiver maybe some one has an idea on what I could check next. |
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In regards to stove piping, Do you mean that the tip of the live round is in the chamber, and the bolt is stuck over the middle of the case/behind the rim, or the tip of the live round is wedged into the gas tube section of the upper. Or, Is this a problem that is being caused by the spent case no clearing the ejection port, and it getting jammed in the action with a live round? If you can give us a better detail on the jam conditions, we should be able to narrow the problem down to a specific area to check. |
| Stove piping --- the spent case is caught by the bolt. The primer end is being help by the bolt and the rest of the case is sticking out of the ejection port. I'm not sure but I think the next round has also been pushed forward. I have to drop the mag to clear it. If I pull the CH this puts the third round into the works. I hope this helps |
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Pull the bolt, and check the ejector to confirm that it is not binding in the bolt face when depressed. If you find that the ejector (#5) is sticking, then you will need to pull it. To so this, you will use a 1/16" punch, and while using a towel to catch the ejector/spring (#5,6), punch the roll pin (#4) that is retaining it. When you go to reinstall the ejector, align the flat of it correctly, then use a spent case on the extractor to retain the ejector in place when you reinstall the roll pin. Note: every once in a while, the ejector is installed incorrectly (it's flat out of position), and this will cause it to bind instead of the basic problems like burs or brass flakes in the ejector channel.  Also, with the rifle unloaded, pull back on the charging hand and confirm that the front face of the bolt stops/limits out in from of the back of ejection port about 1/4". If the bolt retracts past the back of the ejection port, this can cause the round to be deflected on the back of port and bounce forward back into the system. |
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To add since I had time last night to ponder over other items: Pull the extractor and check the ends of the claw. You may have an end milling burs on the claw that is digging into the rim, and not allowing a clean pivot release at end of stroke. If needed, use a small file to clean the off the milling burs from the claw and the ends of the rim relief cut. Also, what could be happening is that instead of the case no being correctly retained, then pivoted off the bolt face at end of rear stroke, the case may be being dropped by the extractor during the rearward cycle. To overcome this problem until the chamber polishes out (reason for the extractor to drop the case), a #60 O-ring added around the outside of the extractor spring will increase the tension of the extractor. In time/once the chamber polishes out threw live fire, you should be able to pull the band-aid O-ring since it will no longer be needed. |
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Dano I will check all the things you talked about. BUT, my problem happens with several different bolts and carriers. I have mixed and matched 8 different bolts and carriers even used differents lowers and they came from ar's that work with no problem. When you talk about pulling the carrier back and the face of the bolt should be 1/4" infront of the ejector port. Is that right???? I looked at all 8 of my ar's and none of them line up this way. They are either even or back 1/4" behind the ejector port. Back to my problem-- I am going to try the o-ring and maybe look into a not buffer spring. Any of other ideas |
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If the bolt face is retracting back past the rear of the ejection port, then as the case is pivot off, the case strikes the back edge of the ejection port and can be deflected back into the action. Again, the face of the bolt should be in front of the ejection port when the buffer is bottomed out. Normal distance is around 1/8" to 3/8" of the bolt face in front of the back edge of the ejection port with the buffer bottomed out against the back of the receiver extension. |
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