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Posted: 5/17/2014 5:33:52 PM EDT
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THIS IS NOT A DSA BASHING THREAD - if that is what you are looking for, please move along.
Now that that is out of the way, I wanted to share my recent experience and hopefully it will save someone from being injured, or at least inconvenienced. I picked up one of the DSA ZM4 Uppers a few years ago as an extra, pretty much because they were cheap and I wanted to see how it would do. While it is not one of my primary rifles, I have put a couple thousand rounds through the upper with no issues to date. Reasonably accurate and no mechanical failures (run with the same BCM BCG since the beginning). It's been a solid "beater" and loaner gun for a few years. I have recently upgraded some other rifles and decided to pass on the "hand-me-down" parts. This afternoon, while I was playing in the workshop, I decided to swap out the standard A2 FH on the DSA upper so I dropped it in the vice and was surprised to see that the barrel started to spin. Not the FH, not the barrel nut, the actual barrel. What really surprised me was the amount of force it took - almost nothing, maybe 10 ft-lbs. I have a sneaking suspicion that if I had just torqued hard on the FSB, I could have broken it loose without a wrench. How I never spun the barrel before now is a mystery, I haven't been particularly hard on this upper but I haven't babied it either. 
I jumped on the computer and apparently this was an issue with some of the early nitrided DSA uppers. I'm not sure how I missed it at the time but since these uppers are obviously still out there, I thought I would post this in case someone else has not seen it. CHECK YOUR BARREL EXTENSIONS. If nothing else, try to remove your FH and make sure that the barrel stays put. It's no guarantee that the barrel/barrel extension torque is correct but given how easily mine came off, it's a quick and relatively painless test. I have already emailed DSA but as it is Saturday, I don't expect to hear anything until Monday - hopefully they will make it right. Again, this is not a bash DSA thread. Any manufacturer can have a problem and honestly, I have never heard of one who hasn't. It has been a couple years since this problem was discovered and it looks like it has long since been corrected. I just didn't get the memo and haven't had any reason to discover it until now. The important this is to check your rifles and make sure that you don't have a surprise waiting for you. This simply wasn't something that I have ever worried about - the upper has been stock except for the handguards (MOE) and I have never had it on the bench before now except for cleaning. Given the glut of cheap AR parts and uppers on the market right now, it may not be a bad idea to watch out for this issue, even if it's not a DSA upper. Keep safe and don't forget to check out your gear. |
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Just one more reason to spend the extra money and only buy barrels/complete uppers from known good, reputable manufacturers/assemblers (Colt, DD, BCM, LMT, etc.).
ANY barrel that does this was BUILT WRONG, not just inadequately torqued. The index pin is supposed to go through the barrel extension and seat in a blind hole in the barrel to prevent this exact thing from happening. |
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Can you guys clarify, are these problems happening with DSA and PTAC nitrided barrels or standard (non-nitrided) barrels?
I almost expect this problem from lower quality or less experienced barrel nitriders. But I don't with standard barrels. Thanks. HighSpeedSteel |
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Quoted:
Can you guys clarify, are these problems happening with DSA and PTAC nitrided barrels or standard (non-nitrided) barrels? I almost expect this problem from lower quality or less experienced barrel nitriders. But I don't with standard barrels. Thanks. HighSpeedSteel Has nothing to do with barrels being nitrided, they are just not being assembled correctly period. I would be suspect of EVERY barrel that came from a manufacturer/assembler that let ANY barrel out the door like that. |
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Quoted:
Has nothing to do with barrels being nitrided, they are just not being assembled correctly period. I would be suspect of EVERY barrel that came from a manufacturer/assembler that let ANY barrel out the door like that. Quoted:
Quoted:
Can you guys clarify, are these problems happening with DSA and PTAC nitrided barrels or standard (non-nitrided) barrels? I almost expect this problem from lower quality or less experienced barrel nitriders. But I don't with standard barrels. Thanks. HighSpeedSteel Has nothing to do with barrels being nitrided, they are just not being assembled correctly period. I would be suspect of EVERY barrel that came from a manufacturer/assembler that let ANY barrel out the door like that. if the barrel is nitrided with the extension installed this happens. |
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Quoted:
Can you guys clarify, are these problems happening with DSA and PTAC nitrided barrels or standard (non-nitrided) barrels? I almost expect this problem from lower quality or less experienced barrel nitriders. But I don't with standard barrels. Thanks. HighSpeedSteel Yes - mine is a nitrided barrel and from my limited research, the problem may have something to do with the barrel extension being installed prior to the nitriding process. And yes - it never should have left in this condition, however there does seem to be some correlation between the nitriding process and this loose barrel extension issue. I am not a manufacturer and don't claim to be - I can only speak definitively on this one upper that obviously has an issue. That being said, others have reported this same issue in the past and from what I can tell, it seems to be limited to the nitrided barrels. |
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Quoted:
if the barrel is nitrided with the extension installed this happens. That is not true. The nitriding process has nothing to do with it. Whether or not the barrel extension was or was not on the barrel during nitriding, that barrel was flat out assembled incorrectly. No matter when in the build process the barrel extension is installed, the proper procedure is to install the barrel extension, drill a hole for the index pin that goes through the barrel extension and partially through the barrel, then install the index pin, place the barrel assembly in a jig and drill the gas port in the barrel. |
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Quoted:
That is not true. The nitriding process has nothing to do with it. Whether or not the barrel extension was or was not on the barrel during nitriding, that barrel was flat out assembled incorrectly. No matter when in the build process the barrel extension is installed, the proper procedure is to install the barrel extension, drill a hole for the index pin that goes through the barrel extension and partially through the barrel, then install the index pin, place the barrel assembly in a jig and drill the gas port in the barrel. Quoted:
Quoted:
if the barrel is nitrided with the extension installed this happens. That is not true. The nitriding process has nothing to do with it. Whether or not the barrel extension was or was not on the barrel during nitriding, that barrel was flat out assembled incorrectly. No matter when in the build process the barrel extension is installed, the proper procedure is to install the barrel extension, drill a hole for the index pin that goes through the barrel extension and partially through the barrel, then install the index pin, place the barrel assembly in a jig and drill the gas port in the barrel. Actually, my understanding is that it is the very high heat from nitriding process that causes the barrel extension to loosen. A good manufacturer will retorque the barrel extension AFTER the nitriding process, THEN drill the gas port. If you don't drill the gas port last, (1) the port and barrel extension will not be lined up properly or (2) they will be lined up properly, but the barrel extension will not be tight enough. My guess is that most manufacturers who are new to the concept of nitriding barrels don't know this. This is why I think it's a bad idea for an individual to buy a barrel/barrel extension (assembled) from one place, then send it somewhere else to be nitrided. HighSpeedSteel |
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Originally Posted By HighSpeedSteel
Actually, my understanding is that it is the very high heat from nitriding process that causes the barrel extension to loosen. A good manufacturer will retorque the barrel extension AFTER the nitriding process, THEN drill the gas port. If you don't drill the gas port last, (1) the port and barrel extension will not be lined up properly or (2) they will be lined up properly, but the barrel extension will not be tight enough. My guess is that most manufacturers who are new to the concept of nitriding barrels don't know this. This is why I think it's a bad idea for an individual to buy a barrel/barrel extension (assembled) from one place, then send it somewhere else to be nitrided. HighSpeedSteel Correct, any torque set between the barrel extension and barrel is lost during nitriding due to the dissimilar metals expanding and contracting at different rates. This is why the barrel and barrel extension should be nitrided separately then assembled, torqued, index pin installed and gas port drilled. Also, in the future, use barrel blocks instead of a receiver block when removing or installing muzzle devices. This will keep the barrel from possibly unthreading from the barrel extension if the index pin does not engage the barrel or shearing the index pin. |
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Quoted:
Correct, any torque set between the barrel extension and barrel is lost during nitriding due to the dissimilar metals expanding and contracting at different rates. This is why the barrel and barrel extension should be nitrided separately then assembled, torqued, index pin installed and gas port drilled. Also, in the future, use barrel blocks instead of a receiver block when removing or installing muzzle devices. This will keep the barrel from possibly unthreading from the barrel extension if the index pin does not engage the barrel or shearing the index pin. Quoted:
Originally Posted By HighSpeedSteel
Actually, my understanding is that it is the very high heat from nitriding process that causes the barrel extension to loosen. A good manufacturer will retorque the barrel extension AFTER the nitriding process, THEN drill the gas port. If you don't drill the gas port last, (1) the port and barrel extension will not be lined up properly or (2) they will be lined up properly, but the barrel extension will not be tight enough. My guess is that most manufacturers who are new to the concept of nitriding barrels don't know this. This is why I think it's a bad idea for an individual to buy a barrel/barrel extension (assembled) from one place, then send it somewhere else to be nitrided. HighSpeedSteel Correct, any torque set between the barrel extension and barrel is lost during nitriding due to the dissimilar metals expanding and contracting at different rates. This is why the barrel and barrel extension should be nitrided separately then assembled, torqued, index pin installed and gas port drilled. Also, in the future, use barrel blocks instead of a receiver block when removing or installing muzzle devices. This will keep the barrel from possibly unthreading from the barrel extension if the index pin does not engage the barrel or shearing the index pin. Actually, it should make no difference whatsoever if you use a receiver block or barrel blocks. If the barrel extension is properly installed and torqued to spec, any properly threaded and torqued muzzle device should break loose long before the barrel extension does. I would also think that at those minimal torque values, the chances of damaging your barrel, barrel nut, or receiver are pretty much slim to nonexistent. Obviously, if your muzzle device is pinned/welded/cross-threaded/damaged or otherwise non-standard, then that may change. Assuming a 150 ft-lb torque on the barrel extension and maybe 15-20 ft-lbs on the muzzle device, this should be a non-issue - even with no indexing pin/barrel contact. You could potentially shear a soft pin, but you would have to have a seriously out-of-spec muzzle device and even then, the only way it would happen would be if you weren't paying attention (or using a torque wrench) and monkey-hammered until something let go. The only reason to avoid a receiver block for a simple muzzle device swap would be if you suspected that you had a bad extension but were afraid to find out. And honestly, it that were a concern I would rather know about it instead of avoiding the issue and hoping for the best. Regardless of the type of block used, the muzzle device should ALWAYS break free before the barrel extension. |
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Actually because the parts where designed with parkarization in mind there have been issue with the same parts being nitrided. if i understand correctly, the nitride leaves a harder but thinner coating resulting in looser fits. I have read stories about parts coming loose, such as fsb, because of it. personally i like nitriding more than parkarizing so its best to check every so often ro ensure the fit of parts.
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| while we're on the topic of DSA Barrels, they just sent me a 14 1/2" in place of a 16" BO , after assembly I took it out back on the range to test fire and it wouldn't extract the fired casing, I took a cleaning rod and punched out the case and tried again with different brass - same problem , after several attempts with Federal, Remington and PMC I gave up . After collecting all spent casings i inspected them and all of the appeared to have been fired in a HK 93 , they looked fluted or Heptagon shaped..What the Heck ???? I've been shooting a long time and have yet to come across a fluted ar15 chamber.lol just saying ????anybody got any idea's on this one ?? |
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DiveFlyFun-- Actually because the parts where designed with parkarization in mind there have been issue with the same parts being nitrided. if i understand correctly, the nitride leaves a harder but thinner coating resulting in looser fits. I have read stories about parts coming loose, such as fsb, because of it. Nitride is not a coating and does not leave a coating of any kind. This has been preached for well over a year on this site, yet many still don't understand. |
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Quoted: Nitride is not a coating and does not leave a coating of any kind. This has been preached for well over a year on this site, yet many still don't understand. Quoted: DiveFlyFun-- Actually because the parts where designed with parkarization in mind there have been issue with the same parts being nitrided. if i understand correctly, the nitride leaves a harder but thinner coating resulting in looser fits. I have read stories about parts coming loose, such as fsb, because of it. Nitride is not a coating and does not leave a coating of any kind. This has been preached for well over a year on this site, yet many still don't understand. |
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