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

[Bartholomew Roberts]

Since you called the magazine and confirmed the information, perhaps you could give us the name of the magazine?

Your story sounds like the Small Arms Review test (11 Beta-C mags on full-auto); but temperatures of some parts (gas block) in that test got well above 400F. There was also no continuous monitoring of temperature, they used an IR thermometer. In addition, mags were not fired as fast as possible, there was a 90 second pause between mag changes. Finally, if no part got above 400F and the hottest part could be touched with a bare hand a mere 30 seconds after that, then whatdver that gas block is built of is downright magical.

So if you have not got any details wrong, it must be someone else's 1100 round test of a gas piston; but whose and where was it published?

 

[rangerruck]

it was in one of the major rifle mags, I can't remember the name, and I don't have the mag anymore as I give them away to either the range people or to vet friends of mine.
It sounds like a very similar test to the SAR mag did , though. did the sar mag say that most of the gas impinge rifles failed after 2 or 3 mags?
that the gas impinge rifles had flaming hot gas tubes, and that they were mostly the cause, but not allways, of catastrophic failure?
Did the sar test show slo mo pics of the rifles, and just how flaming red hot the gas ar's were getting, and then show pics of the piston rod ar firing , with no glowing hot parts?
Whether I am off by 10 or 100 degrees, the diff was astounding, by the pics, by the red hot parts, and how the piston ar had no failures, and EVERY ONE of the gas ar's did. I think that is the main thing we are trying to figure out here.
I don't know how hot solid steel, or other parts have to get, before they start to glow red, but this effect did not occur on the piston ar's, and did on every one of the gas ar's. Also remember on a piston gas block, they vent out all excess gas, that does not go out the muzzle, so no other heated gas moves backwards, toward the receiver area. also the gas block usually has more than 1 hole, not just for venting the gases, but to help cool it down faster, which is why they can cool off faster than other solid parts.
now then, I am not saying to throw your gas ar away, you have to be in some pretty serious combat like fireing conditions, to heat up an ar like that.
but even through casual firing, or plinking, it is obivious that a gas ar is going to get way hotter than a piston ar. And simple physics tell us, that all thing being equal, then the piston ar should function a lot longer, a lot better, with less problems, over the long run, than a gas ar.
And so what I am trying to do here, is answer the origional question as best i can, with as much info as possible; the piston ar heats up a lot less , in all the most crucial places, than a gas ar. And also seems to cool down much faster, in the places it actually does get hot.

as far as the bbl/chamber actually getting hotter, because of the gas going through the tube; somehow the gas going through the tube above the bbl, gets the bbl/chamber even hotter.
I suppose it is possible, what with back pressure adding to friction, the gas makes turns around how many corners, before going down the straight part of the tube; every time it turns a corner, it adds to friction and back pressure. and then of course, if the temps increase, which they seem to do , as the gas tube is usually the hottest part measured in an ar, that and the muzzle it seems. Since that really hot gas is going through a even hotter it seems, gas tube, and then hits the bolt key, if that gas then blows out a bit, getting even back onto the chamber area. and then of course the gas tube is going to be radiating heat as well, above the bbl. I suppose this could all be happening, to keep the bbl and chamber even hotter, longer, than it normally would, if the gas tube is close enough to radiate it's heat onto the bbl, and the hotter, pressurized gas blasts back into the key, and rebounds to the chamber a bit. I suppose it is all possible, but I would not bet my life on it; it just seems reasonable that it may actually be happening.

 

[Bartholomew Roberts]

it was in one of the major rifle mags, I can't remember the name

So you can remember the temperature data and methodologies used in the test; but you can't remember the name of the magazine (although you called them to verify all the data)? Can you see why I might be a little skeptical of some of the numbers you are tossing around even before we get into the magical feats of physics involved (like a metal gas block cooling from 400F to touchable with your bare hands in 30 seconds)?

it is obivious that a gas ar is going to get way hotter than a piston ar.

It will be hotter in some areas, like the bolt or gas tube for example. It will be cooler in other areas (like the gas block for example). However I didn't ask about those areas, I asked about the barrel and chamber. I bolded that because people seem to be eager to tell me about how they can hold their bolt in their hand and that isn't the part of the rifle I am interested in.

And so what I am trying to do here, is answer the origional question as best i can, with as much info as possible; the piston ar heats up a lot less , in all the most crucial places, than a gas ar.

Look, I appreciate you are trying to be helpful; but I am more interested in quality information than "as much information as you can vaguely remember reading somewhere" The "information" you are sharing with me is useless to me because even if you did remember one detail correctly, I have no idea which detail that is and it is clear you don't remember a lot of relevant details despite your claims to the contrary.

I'm sure you have a lot of useful information that I could learn from you on a variety of subjects; but your information on THIS subject isn't helpful to me.

it just seems reasonable that it may actually be happening

Obviously, if I thought it was a ridiculous argument, I wouldn't have posted the original question based on that premise. However, having people chime in that they think that is a reasonable possibility isn't what I was looking for. I was looking for hard facts that support that conclusion (or disprove it for that matter).

 

[rangerruck]

sorry I can't remember the mag for you, I go through a lot every month; usually sar, rifle shooter, nra mag, shooting times, petersons, sof, and some others.
and if you read the sar mag, and still have it, you know they compared temps between the two, and they were lower, in all cases, across the board, from the gas ar to the piston ar. In no cases or circumstances, was the gas ar lower in any of the measure temps, as compared to the piston ar. Sorry if that bothers you. It just is, and as the mag said, the hottest part of the piston ar was the gas block, and it did not get near as hot as the hottest parts of the ar gas type. Plus it cooled off PDQ.
As for facts, i am sure they are out there somewhere to tell you exactly, but I am just saying as far as temps rising, if you use your imagination a bit, I say I could see it happening, and it probably does, with a super heated gas tube, radiating heat. I would like to see numbers saying it does not add, so when you or I find out, we'll know 100% for sure. but as it is right now, I say it does
happen, or I would at least bet that it does happen... put it that way.
As far as the chamber goes, both mags said the chamber was cooler on the piston ar,
no need to look for other info on that one, just to worry about the bbl now.

 

[Bartholomew Roberts]

and if you read the sar mag, and still have it, you know they compared temps between the two, and they were lower, in all cases, across the board, from the gas ar to the piston ar.

Actually I did read the SAR article (and you can too, the link to it is in THIS thread) and again, you are incorrect. The SAR article reported the gas piston having a higher temperature at the gas block (where the gas vents) and the direct impingement having a higher temperature at the bolt (where the gas vents). No big surprises there.

As to the "higher" temperatures elsewhere, several of them were not all that high (i.e. the barrel which wasn't much more than 10F difference between the two and probably well within the margin of error for reasons I've already explained in this thread).

I would like to see numbers saying it does not add, so when you or I find out, we'll know 100% for sure. but as it is right now, I say it does

The SAR article with the temperatures and data has been linked in this thread - twice. If you would like to see the numbers on a gas piston firing 11 Beta-C mags, they are in that link. However since only one M4 was tested and it had a burst gas tube at 264 rounds, I don't think you'll find much. You can check out the "M4 Test to Destruction" thread if you would like to see what happens to an M4 fired at twice the rate of fire in the SAR test with a good quality gas tube.

 

[SHvar]

Heres your physical impossibility (according to you), cooler than air temps, both bolt and carrier.
This thermometer is in the shade all day, so its actually cooler than air temps Which are about 90f, in the sun a bit warmer, heres the bolt and carrier taken within 2 feet of the thermometer.



The oil keeps the parts cooler, thats one of the functions of oil in moving parts aside from the all important function of lubrication, it helps to remove or draw heat away.
Anyone care to test the temps from their DI AR after firing? The next time I take both to the range Ill test both and take a thermometer along for air temps. Ill test chamber temps, barrel temps, reciever, etc.
Anyone care to see how many rds they can fire through a DI rifle and the bolt carrier/bolt are dry from the oil being burned off? So far Ive fired multiple occasions of 200-250 rds with my gas piston rifle, and posted the results.
I wont grab the barrel, bolt, carrier, etc after firing a DI rifle, not with my hands. Heck, I have pulled the gas plug, piston, and rod after firing my gas piston rifle and it was hot, but within seconds its cool enough to handle, like another respondant mentioned from an article.

 

[Mags]

Great idea Bart! About time we got some hard evidence on this theory.

 

[Owen]

Again, the hottest part of the piston ar, was the gas block, and that was touchable to the hand within 30 seconds

Magic!

 

[benEzra]

The oil keeps the parts cooler, thats one of the functions of oil in moving parts aside from the all important function of lubrication, it helps to remove or draw heat away.
Anyone care to test the temps from their DI AR after firing? The next time I take both to the range Ill test both and take a thermometer along for air temps. Ill test chamber temps, barrel temps, reciever, etc.

Be sure to let the bolt carrier warm to ambient first. The only way it could be cooler than ambient was if the gun started out even cooler.

There is no thermodynamic mechanism by which coating a part in thermal equilibrium with its environment with oil that is also at thermal equilibirium with its environment will reduce the temp of either below that of the environment. On the contrary, to cool something, you have to get fancy with adiabatic compression and expansion, coupled phase changes, or thermoelectric effects; otherwise, the best you can do is to insulate it or shed as much heat as possible to the environment.

But the question in the OP was whether or not the chamber and barrel run significantly cooler with GP vs. DI, all else being equal, and the answer there appears to be "no way."

 

[gvnwst]

Ya know Bart, I am wondering, what would lead someone to the conclusion that the BARREL (and so the chamber) would be cooler, just because the gas system, which is seperate and only connected at a small part, is different? Just doesn't make sense to me... The bolt carrier and bolt, sure, cooler with a GP system, I think that that is pretty well founded, but the barrel..?

 

[waterhouse]

The oil keeps the parts cooler, thats one of the functions of oil in moving parts aside from the all important function of lubrication, it helps to remove or draw heat away.

Even if it drew all of the heat that shooting put into the system, it could not possibly draw heat away from the environment.

In other words, the gun sits out on a 90 degree day until it reaches equilibrium with the environment. All parts of the gun are now 90 degrees. You start shooting the gun. Are you really saying that at the end of the shooting session the gun has cooled off to below 90 degrees?

I think if you can prove this with good instruments you may have a Nobel Prize coming your way. I'm not making fun of you, that's how big that would be. You're taking a mechanical system involving combustion and friction and it is cooling the system. It is simply amazing.

 

[MCMXI]

Heres your physical impossibility (according to you), cooler than air temps, both bolt and carrier.
This thermometer is in the shade all day, so its actually cooler than air temps Which are about 90f, in the sun a bit warmer, heres the bolt and carrier taken within 2 feet of the thermometer.

Oh I see ... your calibrated NIST certified infrared thermometer in combination with your calibrated NIST certified alcohol thermometer are all that's required to convince yourself and others that the bolt can be cooler than the ambient air temperature.

I suggest you take a course in heat transfer. Your claims re the bolt/carrier temps are still IMPOSSIBLE regardless of what you think, believe or claim to have measured.

 

[Maverick223]

Just a thought but it does make since that the bbl (specifically the portion nearest the chamber) would be of greater temperature (with DI) due to contact with the bolt (obviously and indisputably hotter than GP)...by how much I don't know.

Oh, and considering IR thermometers are reasonably accurate (within +/- 1% IIRC) then I'd say the dry bulb thermometer that you stole from Martha Stewart is the origin of the error.

 

[SHvar]

I showed you temps taken, I know from first hand experience that these parts are alot cooler with the GP rifle than DI. Since you dont want to believe me or POF then try it for yourself.
The next time I shoot both Ill take the infared thermometer along and a thermometer to measure ambient (air temps). Ill fire an equal number of rounds, pull the bolt carrier, measure the temps in the chamber, on the barrel (on both) (even though my DI rifle has a 1 inch heavy barrel, opposed to the M-4 barrel on my GP rifle), gas plug, piston, piston assembly, op rod (on the GP rifle). I might even throw in a comparison with a 20" Colt Hbar if I can get it to the range at the same time.
By the way, the air temps are correct Maverick223, there is also another thermometer in the sun that was reading a few degrees higher 10 feet away. Surface and air temps read differently (IR thermometers read surface temps, this is used to test basking spots in reptile cages which always read much higher than air temps, ie ambient temps around the object).

 

[MCMXI]

I showed you temps taken, I know from first hand experience that these parts are alot cooler with the GP rifle than DI. Since you dont want to believe me or POF then try it for yourself.

What are you talking about? I bought a POF upper months before you bought your Bushmaster GP upper. One of the reasons I bought it is that the bolt and carrier group run cooler than those in a DGI upper ... this isn't something that I learned from you and it's not the issue here. The issue is that you're claiming that the bolt and carrier (or any other part of the rifle) are COOLER than ambient temperatures. This is not possible ... that's it, nothing more.

 

[Bartholomew Roberts]

They still teach physics as part of the normal educational curriculum, right?

 

[waterhouse]

I showed you temps taken, I know from first hand experience that these parts are alot cooler with the GP rifle than DI.

I don't think you'll find anyone in this thread arguing that point. As Bartholomew Roberts stated:

The SAR article reported the gas piston having a higher temperature at the gas block (where the gas vents) and the direct impingement having a higher temperature at the bolt (where the gas vents). No big surprises there.

People are arguing that you can't beat the laws of physics and thermodynamics. If the rifle started at equilibrium with the environment, claiming it gets cooler than the environment by firing it is akin, from a physical standpoint, to claiming that your rifle floats because it is immune to the effects of gravity. This is Nobel Prize type, turn the science world on its head stuff you are claiming. Combustion and friction simply don't cool objects off, no matter what oil you use.

By the way, the air temps are correct Maverick223, there is also another thermometer in the sun that was reading a few degrees higher 10 feet away.

How long had the rifle been outside before your reading? Was it delivered to the range in an air conditioned car?

Also, the true outside temperature (what the news reports) is generally taken from a ventilated shady box.

When the thermometer is in the shade, it is reading the temperature of the air around it. When it's in direct sunlight it is recording the air temperature plus it is soaking up radiant energy from the light that falls upon it, reporting a higher temperature. The temperature you use for your experiment should be of the air in a shady, ventilated (but not breezy) area.

 

[jhco]

short answer,chamber yes, Barrel no.

 

[waterhouse]

Just a thought but it does make since that the bbl (specifically the portion nearest the chamber) would be of greater temperature (with DI) due to contact with the bolt (obviously and indisputably hotter than GP)...by how much I don't know.

That does seem like a reasonable explanation for the 10 degree difference Mr. Roberts mentioned earlier. Or if not 10 degrees, probably some portion of it.

 

[Jaws]

Actually things can cool to lower then ambient temperature. Is called "endothermic process".
An endothermic process is one in which heat has to be supplied to the system from the surroundings. The thermal energy (heat) is converted to chemical bond energy.

Some examples:
evaporation of water, forming a cation from an atom in the gas phase, melting ice cubes, conversion of frost to water vapor, mixing water and ammonium nitrate, making an anhydrous salt from a hydrate, melting solid salts, reaction of barium hydroxide octahydrate crystals with dry ammonium chloride, reaction of thionyl chloride (SOCl2) with cobalt(II) sulfate heptahydrate, separating ion pairs,....

Now that doesn't mean the lube for AR15 has this effect, but I don't know.

 

[everallm]

Any lubricant applied does NOT have a cooling affect.

The lubricant will only allow a reduction, in wear, friction or galling. These processes can increase heat in the system but this is small in comparison to the heat from combustion.

The only way in which oil could act as a cooling agent would be if the weapon is bathed in a moving stream of oil, acting as both lubricant and heat transfer medium. Think high speed lathe.

Not however a scenario that lends itself to safe and sucessful weapon firing.....

As for the whole issue of DI v Piston transferring heat to the chamber, two of the major areas have not been really touched on.

The piston, in addition to isolating the chamber from direct high temperature gas input also acts an effective heat sink.

The piston as well as the tube it runs inside both act as a large surface area radiator.

This can be failrly easily seen from from the image below of the XCR, a built from scratch, as opposed to retrofit, piston system, the Op-Rod/Piston as well as the gas tube are significant for heat management.

Lots of mass, lots of radiating surface area

 

[Shear_stress]

I showed you temps taken, I know from first hand experience that these parts are alot cooler with the GP rifle than DI. Since you dont want to believe me or POF then try it for yourself.

The big problem here is that you're using an infrared thermometer with the default emissivity of 0.95 on a metal surface. That value is what you use for organic surfaces, not metal. You need to be careful about this. The bolt has been parkerized, which will help, but any "shininess" or exposed metal *will* skew the results you get. The best way to measure temperature in this case would be to use a thermocouple and data logger.

 

[benEzra]

The big problem here is that you're using an infrared thermometer with the default emissivity of 0.95 on a metal surface. That value is what you use for organic surfaces, not metal. You need to be careful about this. The bolt has been parkerized, which will help, but any "shininess" or exposed metal *will* skew the results you get. The best way to measure temperature in this case would be to use a thermocouple and data logger.

Also, there were no "before shooting" pics, only "after shooting" pics. For all we know the bolt and carrier could have started at 40 degrees F below ambient from being stored in a safe in an air-conditioned house prior to shooting.

Actually things can cool to lower then ambient temperature. Is called "endothermic process".
An endothermic process is one in which heat has to be supplied to the system from the surroundings. The thermal energy (heat) is converted to chemical bond energy.

Some examples:
evaporation of water, forming a cation from an atom in the gas phase, melting ice cubes, conversion of frost to water vapor, mixing water and ammonium nitrate, making an anhydrous salt from a hydrate, melting solid salts, reaction of barium hydroxide octahydrate crystals with dry ammonium chloride, reaction of thionyl chloride (SOCl2) with cobalt(II) sulfate heptahydrate, separating ion pairs,....

I mentioned some of those, the phase changes anyway. Gun oil is not chemically reactive in the firearm environment because if it were, it would quickly degrade and would probably accelerate corrosion to boot.

As I said, for gun oil, there are no thermodynamic processes available to cool the parts below ambient if the parts and oil start out in thermal equilibrium with the environment.

 

[PMROY]

Without getting into the technical stuff and just based on my personal experience, the answer is yes for one and maybe for the other?. As some know, I installed the Bushmaster Gas Retrofit Kit on my XM15-E2S. I just got back from the range and can categorically tell you that the chamber and lower stay way cooler and cleaner. The barrel, seams to be cooler and overall the upper cools a lot faster. I shot the same amount of rounds through the Bushmaster and my 6920. The 6920 was fired first and took longer to cool off than the Gas Piston Bushy. Now,one thing I noticed from the kit, was that there is a single heat shield for the top and a double for the bottom. Space limitations I suppose, but it definitely helps in the cooling. I am not sure if it had double heat shields like the 6920, if that would increase the cooling time. So the only way will be to remove one of the upper heat shields from the 6920 and retest. Dam, more work!

 

[SHvar]

My Bushy GP rifle has double heat shields, so its not the heat shields slowing the cooling process.
The fact remains the GP rifle runs alot cooler in the entire rifle including the barrel and chamber over a DI rifle.
I already posted pics on the temps, Im not going to continue on that subject until I take more pics and show more temps with a few examples in comparison.
Already others are seeing the same differences in temps I mentioned, aside from multiple manufacturers their testing, and aside from multiple independant tests.