View Full Version : Piston -vs- DGI systems test in SAR
Interesting article in the March SAR issue. They ran 1,000 rds through a piston upper and a std direct gas impingement upper. They did 100 rd Beta C mag dumps, full auto, reloading as fast as possible. The results were interesting. The piston upper ran like a striped ape and showed no signs of slowing down. The std upper puked after 264 rds. It had a "gas tube failure", which I take to mean it melted down and sprang a leak somewhere, as it no longer had sufficient back pressure to cycle the bolt.
Temp readings were taken at several locations. The bolt face on the piston upper reached 122 deg F after 1,036 rds. The DGI upper reached a peak of 133 deg F after 264 rds. The chamber temp of the piston gun reached 131 deg F after 1,036 rds. The DGI gun reached 115 deg F after 264 rds. The gas block temps were interesting. The piston upper reached 498 deg F after 200 rds and peaked at 697 deg F after 1, 036 rds. The DGI upper hit 339 deg F after 200 rds.
So the piston upper was found to transfer heat at a much slower rate than a direct gas impingement system. Big duh there. But the interesting thing is the gas block heats up much hotter because the gas is stopping there. The gas block is taking one for the team by absorbing a tremendous amount of heat, as the piston and op rod continue, without the gas, to cycle the bolt. But even at twice the temp of the normal gas block, the piston upper ran like a champ.
So what does this all tell us? The most striking thing that I see out of it is: to run repeated full auto mag dumps like a SOF team doing an IA drill, a piston upper is very desirable. If this very heavy firing schedule is you idea of a good time, a piston upper might be a good idea.
With a std, direct gas impingement system, it would be wise to limit full auto mag dumps to 5-6 30-rd mags. Yeah I know they did it in "Heat", and yeah it looked really awesome, but you will probably damage your weapon doing it.
What about semi-auto fire? I would be interested in seeing what kind of schedule would be equivalent to around 264 rds of full auto fire. I have cranked out over 1200 rds in a 8 hr period in a carbine course, and I never noticed my gas tube glow cherry red, as it did in this test. I would have to assume if a carbine can stick to this kind of schedule, then you will probably be OK in most any tactical situation.
The only time I ever stopped a carbine was was in training, doing a break contact drill, where I went through approx 200 rds of blanks, full auto, which carboned up the reciever so bad, the bolt stuck in the locking lugs. The gas tube was cherry red and the handguards melted down at the front corners.
So while I'm not a big fan of the piston uppers, as yet, I do see their uses for the extreme upper limit of the envelope. They may be the answer to SOF's problems with the M-4.
Yes. This proves it. The millions of people with FA registered lowers, LLs or RDIASs AND millions of dollars to spend on ammo need to buy piston uppers...
I dunno about that, but if you are going in harms way and expect to need full auto fire, then a piston upper makes very good sense.
The std upper puked after 264 rds.
While probably a cool test to conduct, the failure of one upper at 264rds does not give any empirical data with which to hypothesize anything else.
It shows that one upper had a failure at 264rds. That's all, and that's it.
I had mentioned the gas block superheating on piston uppers to someone recently offline. Glad to see that was born out with testing. It means the gas port is also being subjected to superheating. :eek:
I dunno about that, but if you are going in harms way and expect to need full auto fire, then a piston upper makes very good sense.
I think they are currently testing DI uppers under FA over in the middle east right now.
I hear they did this back in the late 60's in a place called vietnam.
Heavy Metal
02-09-08, 19:38
They may be the answer to SOF's problems with the M-4.
Add suppressed fire and you will know why the 416 was born.
I think they are currently testing DI uppers under FA over in the middle east right now.
I hear they did this back in the late 60's in a place called vietnam.
I have about had my fill of your smartass tonight. Its getting old, and getting old fast. Either discuss things in an adult manner, or find somewhere else to discuss.
While probably a cool test to conduct, the failure of one upper at 264rds does not give any empirical data with which to hypothesize anything else.
It shows that one upper had a failure at 264rds. That's all, and that's it.
I had mentioned the gas block superheating on piston uppers to someone recently offline. Glad to see that was born out with testing. It means the gas port is also being subjected to superheating. :eek:
I agree. It's too small of a sampling to make any accurate judgements. That is interesting on the gas block and gas port though. That had completely slipped by me. I wonder how much the wear rate is increased?
I dunno about that, but if you are going in harms way and expect to need full auto fire, then a piston upper makes very good sense.
The two biggest areas I see where a piston setup has an edge on a DI system, is heavy sustained full auto fire, and supressed fire.
One note to all this: the authors claimed they were not looking at barrel heat, per se, but a head - to- head test of the gas systems. It would appear that a piston upper does heat up at a much slower rate, as far as the gas system goes, but would the barrel be just as hot as a DGI system?
According to BR vol. II, the barrel must be brought to a temp of at least 1,100 deg F to lose structural integrity. Gov't testing, in the wake of catastrophic barrel failures of M-4A1's in the early 90's, showed that for a barrel to lose structural integrity, where catastrophic failure would occur, between 540 and 596 rds had to be fired, full auto, in 3 to 3 1/2 minutes. This study resulted in the beefed up SOCOM barrel.
So there is something at work here. These guys got off about twice the rounds necessary to blow a std profile M-4 bbl, with a very similar firing schedule. So it would appear that there is a benefit to keeping the hot gas out of the chamber area.
Be interesting to see where this all goes. For the record, I'm not pimping piston uppers. I plan on keeping my DGI systems running for a long time. I just thought this test was interesting.
Ok, I'll explain my joke and apologize if it seemed I was making fun of Diz.
These tests can be formulated to absolutely destroy one test subject but stay well within the operating abilities of the other. This is just such a test. The testers knew that a few 100 round dumps would cook the gas tube and make the gun appear to be a failure and they did. The pistol doesn't fail the same way.
It makes it look like the DI guns can't handle FA fire when in fact they can- that was my point. The DI guns have been able to handle realistic FA fire for a long time. They've had problems along the way but luckily for all of us fans, they've survived and are still going strong.
This is like the tests that were supposedly set up by a secret branch of the military for suppressors. The test in question was very brutal and when one company tested another company's suppressor in this fashion they were able to destroy it during the legitimate testing. But, when one of theirs was subjected to the same brutal testing, it had it's own problems.
The point of that anecdote was to point out that a test can go way above and beyond what is going to be realistically expected of a product. Basically, you won't find a real soldier putting several Beta C mags through his M4 one after the other to the point of destruction and therefore it's a moot point as to which can survive this test.
welchtactical
02-09-08, 23:19
I dont know why people are SO against the piston guns. I've had several DI ARs and now have several piston ARs. I am now behind the piston ARs. They run smoother, cooler, and far cleaner. What is there to complain about? The only problem with most of the piston ARs is price. The only thing I'm worried about is that all the AR companies will rush to put out piston guns and put out some junk. I'm in the military. I think a great fix for all the problems everyone has with the M16 could be fixed with a 12in Barrelled, 6.8mmspc, LWRC upper, 6.8 drop cam'd ACOG with a J-point, and a quick detachable can on a M4 lower.
which piston upper was that ?
where can I order SAR online ? did they have the MK18Mod 0 article in the March issue ? thanks.
which piston upper was that ?
where can I order SAR online ? did they have the MK18Mod 0 article in the March issue ? thanks.
And what DI gun did they use?
welchtactical
02-10-08, 01:47
I have 3-4 thousand through my 16in 556 LWRC upper I bought a year or so ago with zero problems. I shot this one pretty hard, really hard. I'm getting 3/4 to one inch groups with TAP 60gr {My and it's favorite ammo}. The only time it did anything wierd was when the bolt didnt lock back with one of those super great HK mags. Never repeated. Love it.
Points:
The M4,M16 piston or not, is not a SAW.
I think that on actual break out drills in training or actual combat, the Beta C mags would fail before the M4/M16.
Points:
The M4,M16 piston or not, is not a SAW.
I think that on actual break out drills in training or actual combat, the Beta C mags would fail before the M4/M16.
Ditto.
However I've put 14 mags thru a M4A1 making up for a MG that went down in our CAT car.
How fast? That was 420 rounds- quite a bit more than the 264 the test rifle puked at.
Obviously there are different forces at work here, both physical, and perhaps cynical as well SHZ describes them.
Yes, I find it interesting that these guys made a DGI system puke after only 264 rds. But on the other hand, there were real documented problems with SOCOM smoking through barrels with sustained full auto fire.
I had assumed that a distinguished mag like SAR would not be pushing a political agenda but searching for the truth.
But hate to admit it, SHZ brings up a very valid point, in that this test would have been much more realistic if they had used 30-rd mag dumps. But I'm sure their response would have been that they were testing the gas sysytems not the weapon's realiability, per se.
Thanks for noting the few valid points I was making. I make them very seldom and they are even less seldom noticed. ;)
Basically those guys recreated a "test" I've seen many times where someone knows around how many round it will take to melt a gas tube and that's all they did.
It's a magazine, they get their money from somewhere. There's always an agenda. To most people it doesn't matter and it's an article written for entertainment.
Frankly I'm surprised the DI temps weren't a lot higher after the 264 round stoppage.
264 round sequates to nine mags of ammo. That's a decent sized load out.
Agree that this is more of a test to find out "where the system breaks" as opposed to an operationally realistic test. Also agree that a sample size of one makes this more of a conversational topic than a truly representative finding.
I'll never be in a situation to where I need to break contact, or maintain high rates of sustained fire. Still from my perspective, it's not so much that I'm "anti-piston" (or others for that matter), I just wonder why so many are in my same boat are so "pro-piston". If you look at your operational requirements I think most posters on this forum (maybe that's a bad assumption on my part) would be just as well served by a DI system. If you want a piston, go for it, I just think the DI system satisfies all the requirements for the bulk of the members here.
Very true. We all know full auto fire is very sexy and a hell of a lot of fun. But we all also know that it is hard to sustain, both from the heat generated by the piece, and the logistics of all the ammo required. So we all (grudgingly) agree that semi auto fire is the most tactically, if not practically, way to go. Not to mention full auto weapons are extremely difficult and expensive to run, for us civilians.
There seem to be two sides to this issue. Those that are pushing piston uppers seem to be saying that this is the answer to the DGI weapon's problems. Those that a perfectly happy with DGI weapons are saying "what problems?" I guess I am falling somewhere right in the middle.
The realm of full auto fire, especially full mag dumps, is a rare and unique (but utterly fascinaiting) segment of our population as M-4 users. It may not be directly applicable to us right now, but it sure is interesting.
I appreciate your replies here. Always good to have a crew you can bounce info off and get some analysis.
Here is my thermographic video of a 6921 fired fast as I could for 30 rounds. The auto temp sensor on the camera showed the hottest part of the gun, around the gas block at mid 150's.
http://http://www.youtube.com/watch?v=A5Xm8E-X5Wc
This is a video of a semi Ak, not as many rounds showed fired, but the gas piston is about the same temp here as the DI around the gas block at the corresponding number of rounds fired.
http://http://www.youtube.com/watch?v=SnQcyyDJLCo
I did notice, although it is not shown on these videos that the heat around the piston gas block was significately higher with higher round counts. To me, the weak part in the DI system, if you wanted to call it that, would be the gas tube in high rate/volume of fire. I was not able to duplicate the F/A aspect of it, but it is neat to see how heat affects the different systems.
Very true. We all know full auto fire is very sexy and a hell of a lot of fun. But we all also know that it is hard to sustain, both from the heat generated by the piece, and the logistics of all the ammo required. So we all (grudgingly) agree that semi auto fire is the most tactically, if not practically, way to go. Not to mention full auto weapons are extremely difficult and expensive to run, for us civilians.
There seem to be two sides to this issue. Those that are pushing piston uppers seem to be saying that this is the answer to the DGI weapon's problems. Those that a perfectly happy with DGI weapons are saying "what problems?" I guess I am falling somewhere right in the middle.
The realm of full auto fire, especially full mag dumps, is a rare and unique (but utterly fascinaiting) segment of our population as M-4 users. It may not be directly applicable to us right now, but it sure is interesting.
I appreciate your replies here. Always good to have a crew you can bounce info off and get some analysis.
Yeah, what problem? I don't blow gas tubes often...
which piston upper was that ?
where can I order SAR online ? did they have the MK18Mod 0 article in the March issue ? thanks.
The test was with our P416 gas piston weapon system, which we have been selling since Dec. 2004. :D
http://www.pof-usa.com/images/p9xev.jpg
The temp. reading were very interesting, considering the amount of ammo shot, with 10 Beta-C mag dumps in 10 mins.
How could a carbine weapon system shoot this much ammo, in a short amount of time, without a cook off? :D
Best regards,
http://www.pof-usa.com/images/pofusalogo.gif
Like all integrity tests , this exercise puts the test subject through conditions it is unlikely to ever see in the "real world"
I have never understood the rationale for running a head to head integrity test but I am an engineer...I am not in marketing:)
I can tell you from experience that while integrity tests make you feel all warm and fuzzy about your "product" Mr. Murphy still manages to create "issues"
Focused simulations...as in testing the product to real world conditions tell you much more about the likely failure modes. Granted, that testing should be done to extreme real world conditions but I don't think that was the case here
Short of clearing brush I cannot imagine any need for simply hosing that many rounds downrange. I would be surprised if the operator was in any condition to continue afterwards:D
I wonder what type of accuracy was achieved:p
Either way it would have been fun to watch
Someone ought to inform these guys that their rifle should have puked.
http://www.imisp.com/~noveske/shot3.wmv
300rnds FA in well under 1.5 minutes.
The test was with our P416 gas piston weapon system, which we have been selling since Dec. 2004. :D
http://www.pof-usa.com/images/p9xev.jpg
The temp. reading were very interesting, considering the amount of ammo shot, with 10 Beta-C mag dumps in 10 mins.
How could a carbine weapon system shoot this much ammo, in a short amount of time, without a cook off? :D
Best regards,
http://www.pof-usa.com/images/pofusalogo.gif
Interesting brake. More pictures?
Since we are on this topic, I am curious as to what you guys think about the interview with L. James Sullivan and his criticisms of the M16? I know that much has been kicked around here and other places about direct gas vs. piston, but I will say that when I fired the 416 I did indeed notice that the weapons seemed cooler and definitely much easier to clean.
I just wish that PoF would reduce their delivery arrival time so I could get a PoF416 and run through the ringer myself.
a POF P-415-16-P9SX-223 to me, the test says it all. After researching M4/AR15's and the operating systems, reading soldiers complaints about them, the piston operated rifle made the most sence to me, if I had to stake my life on either system, the piston system would be my choice hands down. The issues with the M4 are real and I'm glad to see that the government is doing testing on piston operated guns and hope they are smart enough to do the upgrade. one of the reasons the AK-47 has the reliability rep it does is due to the piston operating system. ( I know I'm stating the obvious here ) Just my $5.56 worth
Dan
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