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Discussion Starter · #1 ·
Constructor (and others), what is your opinion on this item? I have done some digging on 304 AISI once QPQ'ed, and it appears from a "lab" perspective, to not be all that bad, but I am curious about any testing/ideas that you and others have kicked around?
 

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I have nitride tubes on 3 of my 4 - 6.8's and have built several with them. I prefer them being black and subdued.


Sent from a final firing position, the crosshairs are on you!
 

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Constructor (and others), what is your opinion on this item? I have done some digging on 304 AISI once QPQ'ed, and it appears from a "lab" perspective, to not be all that bad, but I am curious about any testing/ideas that you and others have kicked around?
You trade the corrosive resistance properties of the stainless for the corrosive resistance properties of the Melonite. IMO Melonite will not weaken the tube but it will not help other than turn it black. Gas tubes fail from full auto fire turning the tube red hot then rupturing the tube. It will happen either way.
 

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I have been using them for years with no problem for the sole reason that they are black.
 

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Discussion Starter · #5 ·
You trade the corrosive resistance properties of the stainless for the corrosive resistance properties of the Melonite. IMO Melonite will not weaken the tube but it will not help other than turn it black. Gas tubes fail from full auto fire turning the tube red hot then rupturing the tube. It will happen either way.
I bought a DD 304 stainless and a SLR 304 QPQ stainless tube. I also have a propane torch. Now, I am going to clamp both in a vice, put the flame to them, and see which one goes floppy first, or if they go at the same time. It's not representative of burst resistance, but I have never seen a gas tube burst before sagging.
 

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I bought a DD 304 stainless and a SLR 304 QPQ stainless tube. I also have a propane torch. Now, I am going to clamp both in a vice, put the flame to them, and see which one goes floppy first, or if they go at the same time. It's not representative of burst resistance, but I have never seen a gas tube burst before sagging.
Let us know how that turns out...good idea
 

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I'm not saying I'm not interested in the results, because I most definitely am.

But it seems to me, that unless you have a full auto lower and are in the habit of doing MANY mag dumps in a row, this is well into the realm of over testing.

Now that I have that part out of the way... I'll go make some popcorn and await the result of your test!
 

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I just paint my standard, stainless tubes black with High Temp matte black grill paint. Haven't had any issues yet and I've gotten them quite hot.
 

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Discussion Starter · #9 ·
I'm not saying I'm not interested in the results, because I most definitely am.

But it seems to me, that unless you have a full auto lower and are in the habit of doing MANY mag dumps in a row, this is well into the realm of over testing.

Now that I have that part out of the way... I'll go make some popcorn and await the result of your test!
Well, LMT went to a QPQ'ed gas-key, and has shown that it lasts longer, and produces less wear. Coefficient of friction of QPQ on QPQ is lower than stainless on QPQ. Also, the surface of the QPQ'ed 304 AISI gas tube will be harder. This means that the little mushroom which seals in the gas key will take longer to wear down. This is a real and tangible benefit for those who shoot/train a lot, as well as departments that issue M4 type weapons, as I have heard from many who work on LE weapons that it is common to have to replace a gas-tube who's only issue is the above wear. So, even if full-auto fire is not a concern, and aesthetics don't matter, this is a legitimate issue and the QPQ'ed gas tube provides a solution.
 

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Well, LMT went to a QPQ'ed gas-key, and has shown that it lasts longer, and produces less wear. Coefficient of friction of QPQ on QPQ is lower than stainless on QPQ. Also, the surface of the QPQ'ed 304 AISI gas tube will be harder. This means that the little mushroom which seals in the gas key will take longer to wear down. This is a real and tangible benefit for those who shoot/train a lot, as well as departments that issue M4 type weapons, as I have heard from many who work on LE weapons that it is common to have to replace a gas-tube who's only issue is the above wear. So, even if full-auto fire is not a concern, and aesthetics don't matter, this is a legitimate issue and the QPQ'ed gas tube provides a solution.
Interesting, I was thinking there was a concern with this over the burst strength of the gas tube when hot due to full auto fire. I had not thought of the wear from the gas key, certainly QPQ would help that. Any idea how many rounds are we talking about for a maintenance cycle on gas tubes?
 

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Discussion Starter · #11 ·
Interesting, I was thinking there was a concern with this over the burst strength of the gas tube when hot due to full auto fire. I had not thought of the wear from the gas key, certainly QPQ would help that. Any idea how many rounds are we talking about for a maintenance cycle on gas tubes?
Depends on carrier alignment. I already have live fire data that indicates the qpq 304 tubes are superior at handling all out abuse. That said...I want to also test their corrosion resistance, both before and after being heated beyond their temper points, as compared with AISI 304 non qpq.
 

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Discussion Starter · #12 · (Edited)
The gas tubes arrived today. I heated them with the propane torch for a good 5+ minutes, but neither would do more dramatic than turn cherry red. No sagging or deformation of either. I am now corrosion testing them. The DD gas tube did "glow a little brighter", but that may just be the black color of the nitride tube masking the glow. I didn't find it significant. I am going to pass on uploading the video, because it's literally like watching paint dry. I'll upload the corrosion video if it is any more significant. If not, a text reply.
 

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The gas tubes arrived today. I heated them with the propane torch for a good 5+ minutes, but neither would do more dramatic than turn cherry red. No sagging or deformation of either. I am now corrosion testing them. The DD gas tube did "glow a little brighter", but that may just be the black color of the nitride tube masking the glow. I didn't find it significant. I am going to pass on uploading the video, because it's literally like watching paint dry. I'll upload the corrosion video if it is any more significant. If not, a text reply.
So since they didn't deform under heat or collapse, if the QPQ tube passes your corrosion test, will that make them "Unobtanium" material?

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Discussion Starter · #14 ·
So since they didn't deform under heat or collapse, if the QPQ tube passes your corrosion test, will that make them "Unobtanium" material?

Sent from a final firing position, the crosshairs are on you!
Haha, I run QPQ carriers, and QPQ likes QPQ (unlike some metals/untreated metals which gall). I will likely include SLR's QPQ tubes in anything I assemble.

This far, it has done very well in my corrosion test. Pictures to follow. I am currently being as mean as I can to the gas tubes, laying a sopping wet square or 3 of toilet-paper over them. Soaked with salt and ammonia. I really can't think of anything more abusive within reason.
 

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Haha, I run QPQ carriers, and QPQ likes QPQ (unlike some metals/untreated metals which gall). I will likely include SLR's QPQ tubes in anything I assemble.

This far, it has done very well in my corrosion test. Pictures to follow. I am currently being as mean as I can to the gas tubes, laying a sopping wet square or 3 of toilet-paper over them. Soaked with salt and ammonia. I really can't think of anything more abusive within reason.
That should tell the tale.

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Discussion Starter · #16 · (Edited)
That should tell the tale.

Sent from a final firing position, the crosshairs are on you!
Sorry, chemistry never was my forte, that said, ammonia isn't going to kill stainless steel. I just switched to super-saturated salt solution with water. Added a phosphate stripper clip sans oil for a "witness".
 

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Discussion Starter · #17 · (Edited)
After almost 18 hours under damp saline saturated paper, neither gas tube showed any significant corrosion, although one spot was noted on the qpq tube, and a red stain was left under part of the non qpq tube. It would appear that qpq does cause a slight degradation of corrosion resistance in a bracken environment where 304 AISI gas tubes are concerned. Both Tom of Spike's Tactical, and another tech support correspondence with another industry leader indicate qpq has increased significantly the abuse their gas tubes are capable of withstanding. The second company does not offer a qpq tube at this time, so no financial interest motivated their correspondence with me. Thus far, my opinion is that a QPQ gas tube is an improvement, all except where corrosive ammunition may be used.

 

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Discussion Starter · #18 ·
I finally tired of dicking with said gas tubes. I grasped them both (one at a time) at each end, and bent. The QPQ'ed and the non-QPQ'ed tubes both bent most dramatically (they bent along their length, but even moreso) at the point where they were heated. However, there was an extremely notable difference in the force required. The QPQ'ed tube felt to take 2-3x the pressure to bend, at least. I don't have calibrated hands, but it was very notable, not something like comparing a 16oz and 18oz object to each other in either hand, but more like comparing the size of a golf ball in one hand to a tennis ball in the other. The QPQ treatment DEFINITELY did something to strengthen the tube, especially at the point where I heated them.

I then continued to worry them back and forth until I snapped them. I noted that there was evidence of corrosion inside the QPQ tube, but not inside the non-QPQ tube.

This leads me to my final opinion on the matter, that if you want to have a build that will sustain higher heat without the gas-tube being a failure point, QPQ gets the nod. If you want to run corrosive ammo through the weapon, a regular gas-tube would better suit you. If you want to run it hard, hot, and corrosive, I'd go with an inconel gas tube.

 

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Use of an M-16/M-4 in maritime conditions certainly happens quite a bit. I can't tell you how much time I spent in the Atlantic or Med with my M-16A2 dripping from salt spray. I don't recall ever having rust on my firearm. Although I think one of our M240G acquired some.

Anyway... How much corrosive ammo is actually out there for 5.56/.223 Rem? The US Military stopped using ammo with corrosive primers somewhere in the middle of the 1950s I think. It would have been nearly 10 years later that the 5.56/.223 was developed. Even the cheapest of the commercial imported ammo that I have seen has been non-corrosive. Is there a stockpile of corrosive ammo from Latveria or something?
 

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Discussion Starter · #20 ·
Use of an M-16/M-4 in maritime conditions certainly happens quite a bit. I can't tell you how much time I spent in the Atlantic or Med with my M-16A2 dripping from salt spray. I don't recall ever having rust on my firearm. Although I think one of our M240G acquired some.

Anyway... How much corrosive ammo is actually out there for 5.56/.223 Rem? The US Military stopped using ammo with corrosive primers somewhere in the middle of the 1950s I think. It would have been nearly 10 years later that the 5.56/.223 was developed. Even the cheapest of the commercial imported ammo that I have seen has been non-corrosive. Is there a stockpile of corrosive ammo from Latveria or something?
People use these on 5.45 builds because they think qpq = corrosion proof. However, qpq almost always lowers the corrosion resistance of stainless steels, as demonstrated.
 
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