Do gas pistons keep the barrel and chamber cooler than direct impingement?

[Bartholomew Roberts]

In another thread, someone made the statement:

The piston rifle does not have the DI system cycling hot exhaust gases in its reciever, and above its chamber, therefore the level of heat exposed to the chamber and barrel are much lower. Try it for yourself. In fact the exhaust gases only travel around 2 inches or less in a gas piston rifle above the port in the barrel, therefore 3/4 of the heat, carbon, exhaust, etc are vented directly in front of the front sight area in a spray.

So the claim seems to be, that by taking hot exhaust gases from the chamber and barrel and running them over the outside top of the barrel, the barrel is somehow kept hotter than when these gases are used to cycle an oprod and vented at the gas block.

Personally, it seems strange to me to argue that the barrel and chamber (the source of the initial heat in both cases) gets hotter because of how the excess gas is used to cycle the weapon; but I am interested in seeing any data or studies that support that conclusion.

Does anyone have any? I would think with the popularity of gas piston ARs these days that this would be a big selling point; but I haven't seen any manufacturers claim it in their marketing material either so I remain skeptical.

 

[Shung]

my answer to the title is "not really" ...

I think not at all for the barrel, and, a little bit for the chamber.. the main part that should stay cooler is the bolt assembly and upper receiver.

 

[benEzra]

The receiver and bolt carrier assembly, yes. The chamber and barrel, absolutely positively not.

The chamber and proximate barrel are directly heated by the thousand-degree, 55,000-psi gas inside, not by the minuscule amount of cooler, lower-pressure gas that comes back through the gas tube.

 

[JDGray]

Don't know about the chamber, but the gas block or FSB, gets very, very, HOT!!! Touched one yesterday!! Looks like a very easy system to convert over to

 

[praharin]

Looks like a very easy system to convert over to

And yet...

 

[carbine85]

No, the barrel, piston, and front sight block get hot as expected. There isn't any real heat in the receiver or bolt assembly. The on I shoot got a little hot at the front of the hand guard near the front sight. I think it was the PWS conversion system.

 

[briansmithwins]

Don't know about the chamber, but the gas block or FSB, gets very, very, HOT!

True with an AK also.

I suspect that a fit man can't carry enough ammo to make a DI AR quit working from fouling. External sand and dust can make ARs (of anything else) quit working. Gas piston conversions do nothing about the ARs lack of clearance for external debris that get inside the rifle. BSW

 

[SHvar]

Note, there is a huge difference between conversion kits and gas piston AR rifle designs.
But multiple manufacturers have already proven that they function wet, sandy, dirty, etc far more reliably than DI versions. I do suspect that a large part of the DI system jamming with debris has to do with cooked oil, carbon fouling, and outside dirt/debris combined. 3 times the reliability in sand and grit, the ability to fire soaked without the rifle exploding. In fact I saw an H&K416 fired underwater, it fired a single shot underwater (completely submerged), the action did not cycle properly but when removed from water, manually cycled it then fired normally.

A good indicator, oil cooks off fast under increased heat, in fact it doesnt take many rounds through a DI rifle to have the entire bolt carrier, and bolt completely dry, this increases temperatures through friction.
With a GP AR the entire bolt, carrier, reciever, are wet with the same thin coat of oil you put there originally, hundreds of rounds later, and they are spotless as far as carbon, fouling, cooked oil. The bolt carrier, and bolt itself are cool after a few hundred rds, infact with a very thin coat of oil on these parts, the temps are below the air temperature outside the rifle on a warm day.
Ive read that during testing, GP AR rifles produce lower barrel and chamber temps, therefore the life of these parts is much increased (keep in mind that they are referring to rifles being fired full auto for durability, not semiauto, or 3rd burst).
The gas block is hot on a GP rifle, and the barrel around the block is noticeably warmer, but the rest of the barrel is cooler than a comparable DI rifle with the same amount of rds fired (not enough to prevent hurting yourself if your not careful, but enough to increase barrel life).
I have both DI and GP ARs, I like both for many reasons, but the GP rifle has noticeable differences in operating temperatures almost everywhere in the rifle.
Ive never had a DI AR based weapon fail, so keep in mind they are very very reliable.
Seeing is believing, I was skeptical until I tried for myself.

 

[rangerruck]

much more so.... not even close. I read a mag about 1 year ago, testing both types ar's , 1 piston ar, against several top gas ar's. all used beta c mags.
all gas ar's failed full auto testing, after about 2 or 3 mags. they did nighttime, slow motion heat photography video. the gas ar's pics were astounding to say the least. muzzle became pretty red hot, gas tube became supernova red hot, and chamber became slightly red hot, as did the carrier key. You could actually see the gas tube red hot and glowing, through the front stock/handguards!!!!!
the piston ar/ except for 1 bad mag, dumped without stop, all 11 mags in a row without stopping. it was also only lube once at the beginning, as well.
all parts mentioned above on the gas ar, were between 400 and 800 degrees, and took a lot of time to cool down.

the piston drive? chamber, was touchable to the hand in about 10 seconds. no wait time at all for the carrier, gas block was touchable in about 30 seconds, which is the hottest part on the piston drive. no part temperature exceed 400 degrees.
the gas ar, the gas tube was allways hottest, stayed hottest longest, and was generally the part that had a catastrophic breakdown first.

 

[HorseSoldier]

If the gas piston rifle fired 1100 rounds full auto without significant cooling breaks, I'm inclined to say something sounds fishy and unscientific about the test . . .

 

[waterhouse]

The bolt carrier, and bolt itself are cool after a few hundred rds, infact with a very thin coat of oil on these parts, the temps are below the air temperature outside the rifle on a warm day.

Are you saying that the rifle was outside on a hot day and after firing the parts were cooler than the ambient temperature or are you just saying that the parts are generally cooler than, say, 106 degrees F?

 

[Bartholomew Roberts]

But multiple manufacturers have already proven that they function wet, sandy, dirty, etc far more reliably than DI versions.

Is that because they use a gas piston or was it because those manufacturers use a different bolt and barrel extension that better tolerate external debris?

the piston ar/ except for 1 bad mag, dumped without stop, all 11 mags in a row without stopping. it was also only lube once at the beginning, as well.

The piston AR fired 11 Beta-C mags in a row without stopping and never reached a temperature of greater than 400F anywhere on the rifle? That would be a miracle of the first order. Are you sure you have those facts remembered correctly and what magazine was this in?

 

[gvnwst]

The piston AR fired 11 Beta-C mags in a row without stopping and never reached a temperature of greater than 400F anywhere on the rifle? That would be a miracle of the first order. Are you sure you have those facts remembered correctly and what magazine was this in?

I do believe he has his facts wrong, but IIRC, this is the test that POF did, M16A2 vs one of their P-416 rifles.

 

[MCMXI]

I got in a heated discussion about the benefits of DGI vs. GP ARs a few months back on this board. Lots of anecdotal evidence but zero facts or data. Here is a link to one of the articles on the POF web site.

http://www.pof-usa.com/articles/P416Torture.pdf

There are more articles HERE.

The bolt carrier, and bolt itself are cool after a few hundred rds, infact with a very thin coat of oil on these parts, the temps are below the air temperature outside the rifle on a warm day.

Physically impossible unless the rifle was sitting in a cooler full of ice prior to being fired!

 

[Bartholomew Roberts]

Hmmm, looking at the POF test shows about a 10F difference in chamber temperatures at around 300 rounds. Even if that is a valid difference not within the range of error for measuring with an IR thermometer, it seems hard to believe that a 10 degree difference in a relatively extreme test is going to give the gas piston any edge in barrel life.

Having used an IR thermometer to do barrel temperature comparisons myself, I can say they are a lot handier than thermocouples; but the readings fluctuated enough on the thermometer I used that getting a consistent read was difficult.

As far as the test, I don't think it is any shocker that a several hundred dollar piston will outlast an $8 gas tube in a test. Although clearly gas tubes can be built that will outlast the barrel (see M4 test to destruction thread). It would have made for a much better comparison if SAR had used a similar gas tube.

 

[Mags]

What we need is someone with a DI rifle and a GP rifle to do you an evaluation running the same amount of rounds through both rifles and then provide the results. Hmmm maybe its time for me to purchase a POF?

 

[gvnwst]

What we need is someone with a DI rifle and a GP rifle to do you an evaluation running the same amount of rounds through both rifles and then provide the results. Hmmm maybe its time for me to purchase POF?

If someone gives me the ammo, i got a POF...

 

[Mags]

If someone gives me the ammo, i got a POF

Well there goes my excuse...

 

[gvnwst]

Na, you need one just cuz they is da awzumsness.

 

[SHvar]

The days Ive fired my GP rifle were in the high 80s to low 90s, the bolt carrier, and bolt were cool to the touch, in fact noticeably cool to the touch, both still covered in a clean slick coating of oil after over 200 rds. So its not physically impossible, try for yourself.
As soon as I fired the first 200 plus rounds I removed the bolt carrier and was skeptical, I grabbbed it ready for it to be hot, but it was wet and cool.
The problem for those who have not experienced this yet in person is that they are so used to DI AR type rifles that they cannot fathom that there is THAT much of a difference.
The only part of the entire upper reciever that gets a bit of dirt on it even is the very face of the bolt, and a bit inside of the chamber. The entire rifle aside from the gas piston assembly, and the barrel (mostly around the piston assembly), front sight area, is cool or just warm.
This was after 250 rds of Brown Bear and PMC, these were taken before I cleaned it. Note the dust sticking slightly to the coating of oil which gives a funny appearance in this picture, I guess the camera couldnt decide how it wanted to adjust for these pics (maybe not the best light for it). Its pretty obvious where the actual carbon is, what little is actually there. If this area actually got hot there would not be oil left behind like in a DI rifle.

Although difficult to see, notice the shiny coating of oil even on the slightly dirty bolt face. Also notice my fingers are not covered in carbon by handling this, also still coated in oil from before shooting, not cooked off and dry from the heat.

If comparing a POF rifle with their cold hammer forged fluted barrel to a DI rifle the DI rifle would have to have POFs heat sink, the barrel, the coatings, etc. Even my Bushy has the POF coatings (you can see it in the piston assembly, and under some other parts of the rifle).
I have seen beta mags being dumped in a few POF rifles, alot of rds, and no problems, very well built rifle. Nice price for comparison also.
POF torture test 1036 rds full auto, 9.25 inch barrel, all Russian wolf, temps under 800.
http://www.pof-usa.com/articles/P416Torture.pdf

 

[Bartholomew Roberts]

Yes, I think we all understand that using hot exhaust gases piped directly onto the bolt in order to unlock the bolt will make the bolt hotter than using the gases to cycle an oprod and push the bolt back (which in turn makes the op rod/gas block interface hotter).

I am not debating that at all. What I am debating is the contention that the barrel and chamber of a rifle stay cooler because a gas piston is used instead of some other operating system.

The SAR test seems to offer a tiny sliver support for that since it does show a 10F difference in favor of the gas system after 300 rounds; but that can also be explained by:

1. Technical error in temperature measurements
2. Heavy-profile fluted 16" barrel on the POF-416 instead vs. M4-profiled 16" barrel. More mass means it takes longer to heat the same 16" barrel up.
3. Difference in friction caused by barrel coating

Again, even if the SAR test does show a valid difference, what are the practical results of a 10F improvement over 300rds of 100rd bursts?

 

[MCMXI]

The days Ive fired my GP rifle were in the high 80s to low 90s, the bolt carrier, and bolt were cool to the touch, in fact noticeably cool to the touch, both still covered in a clean slick coating of oil after over 200 rds. So its not physically impossible, try for yourself.

But the point is, the coolest the bolt and carrier could be is AMBIENT temperature i.e. high 80's to low 90's based on your description. The reason why the bolt and carrier felt cool to the touch is that steel has a MUCH higher coefficient of thermal conductivity compared to human flesh. So your body at 98.6F gives up heat to the bolt and carrier at let's say 90F. What you're feeling is heat transfer from you to the bolt/carrier which your body interprets as touching a surface that "feels" a lot cooler than it is. I have no problem believing that the bolt/carrier were around ambient temperature but they definitely were not BELOW ambient temperature ... that's the only point I'm trying to clarify here.

 

[waterhouse]

The days Ive fired my GP rifle were in the high 80s to low 90s, the bolt carrier, and bolt were cool to the touch, in fact noticeably cool to the touch, both still covered in a clean slick coating of oil after over 200 rds. So its not physically impossible, try for yourself.

Firing a rifle, no matter what the operating system, is certainly not a cooling process. The coolest the metal could be is the same as the outside temperature, at least assuming that the rifle started out in equilibrium with the environment. Metal moving on metal, even with a thin coat of oil, does not cool the metal down. It is physically impossible for the metal to be cooler after firing than the ambient temperature.

The problem for those who have not experienced this yet in person is that they are so used to DI AR type rifles that they cannot fathom that there is THAT much of a difference.

No, I can understand that your bolt and carrier are cooler than the same parts on a DI rifle. I can't understand how they could be cooler than the ambient temperature.

ETA: should have read all the posts, 1858 beat me to the exact points.

 

[Maverick223]

Na, you need one just cuz they is da awzumsness.

How can you argue with that? I have toyed with the thought of getting one (a gas piston AR) in 6.5 Grendel. Seems like a great moderate-long range plinker. I would love a HK 416, but am pretty well set on the caliber, so who should I turn to?

 

[rangerruck]

Nope, sorry, I am not wrong, I am not thinking of the wrong info or temps, just the opposite. Becuase I was so impressed with what I was reading, I re read. and then I also called the mag, and asked them. the testing was all legit, using multiple electronic temp monitors, constantly attached to the rifles, or on tables, where rifles were immediately put down, and tested, and retested.
this test was also done, outside, at night , with ambient temps.
Again, the hottest part of the piston ar, was the gas block, and that was touchable to the hand within 30 seconds.
to answer one of Bartholoms' questions, the chamber on the piston ar was astonishingly not hot.
if i rr, it never got above 200 degrees at anytime, and now that I think about it, Ithink it hovered around 130 to 150, because it just did not stay hot continuoulsy, for any lenght of time. the firing is just too fast, AND THE BRASS EATS UP THAT HOT TEMPS. Dudes in the test would sit down the rifle, open it up , pull the bolt and carrier out, and were putting their fingers on the chambers/faces, as soon as possible, no one got burned.