DI or Piston?

[JC5188]

Each family of weapons is a unique compound machine. But they are made up from the same basic six simple machines. They all follow the same laws of physics. Once that is understood, it's easy to see the similarities. It becomes easy to understand, for example, that the gas holds more heat at the gas block and how it cools as it travels through a tube. It becomes obvious that the face of a small diameter piston exposed to gas with more heat is going to get hotter than the face a larger diameter piston exposed to gas holding less heat.

That does not translate into "A" is bad and "B" is good, it is a simple statement of fact. People started repeating the marketing hype of how a "piston" system is cleaner and cooler than a "DI" (sic) system without looking at the science. Just like they started repeating how a "piston" system is heavier and has more recoil, again without looking at the science. Baloney!

The ammo is going to generate the same amount of energy in the form of heat and recoil and the same amount of fouling no matter what gas system the weapon it's fired in uses. If there is extra recoil because the reciprocating mass is moving too fast and bottoming out too hard, the weapon is over gassed.

A "piston" AR might be two, three or maybe four ounces heavier because the op rod might be that much heavier than the gas tube it replaces. Most "piston" uppers that are heavier have heavier profile barrels.

Because of your challenges, I have taken a closer look at the science because I know the science is right. Examining the science closer has helped me understand it better. Pistons still get heated and coated with fouling whether they're part of a long stroke or short stroke system, or if the piston is in the carrier or the gas block. Lube helps keep fouling moist and soft. Heat causes fouling to dry and harden. Do any of the systems you're talking about change these facts? Don't be dismissive. Show me the science

I don't need science to see that a short stroke piston AR has less fouling in the uper and lower than a tradition DI gun.
That is a fact, and if you had had anything but theoretical knowledge on the subject matter, you would also have seen this. Get one and shoot 1000 rounds side by side, and show me the difference. If you deny this, you clearly show that you don't know what you are talking about

There is less heating of the bolt, bolt carrier and associated parts on a short stroke piston gun than there is on a DI gun. That is fact, and has been measured using heat imaging. I'll try to dig up the images later today.

Barrel, chamber and gas block temps run about the same, depending on barrel profile. I'll try to dig up the images later today.

These pics, no BS, are of a rifle that has over 500 rounds without cleaning...







Even if all other attributes are insignificant to the end use of the tool (hotter/cooler/heavier/lighter/etc), or subjective to the user (felt recoil/weight/etc), the gun runs cleaner. Most fouling is vented into the air. I would assume that since the piston in guns like an FAL are contained within the tube, they capture most of the fouling that is expelled at the gas block. That isn't the case for these AR types.


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[ABNAK]

Piston or DI, the carbon goes somewhere. In a plain-Jane AR it's in the upper and BCG. In a piston gun it's on the piston and likely blown all under the handguard/rail. One could make the argument that excessive carbon fouling on a DI gun is putting it where the "guts" of the weapon are, i.e. the operating parts. Yeah, but dumping it all over the piston and inside it's "sleeve" is also a working area necessary to function.

I'll say this, having experience with most of the existing piston systems for AR's at one point or another: the HK416 (or MR556) with a vented gas block blows the majority of excess carbon fouling forward and upward, away from the weapon. The non-vented blocks, which are on the 10.5" guns, will indeed blow all over under the handguard. Now the Colt 6940-P, if memory serves (I had one a while back), expels the gas out side ports on the gas block which is not under the handguards, so it stays pretty clean as well.

Why the majority of piston makers can't vent the excess gas externally as opposed to under the handguards (which are usually not readily removable) is beyond me. If it's a cup-over-spigot design like the LWRCi then there's not much that can be done about it.

[Arctic1]

ABNAK:

The gas vents out under the handguard as the piston is pushed rearwards by the gas pressure. Some gas escapes there. Most of it is ejected out of the port on the gas block.

There isn't much fouling on the piston itself, most of it is just discoloration.

This is 416 specific.

[Arctic1]

You're correct in the observations, and you will be rebutted with the statement that those observations have no practical consequences, which is also correct. The bolt is hotter - so what? Carbon in the upper - so what?

I am not arguing those statements at all, and have never said that they are of practical concern.

But to say that a piston gun is just as dirty as a DI gun is nonsense. It is not.

[scottryan]

Agree with the first statement but curious why PWS doesn't make cut? They have the most elegant system by far. And servicing the piston and piston tube is pretty straightforward.

Because the PWS system uses a operating rod attached to the top of the carrier with cheap YFS brand screws.

[JC5188]

As per the OP...

I'm not advocating the "piston" over "DI". I own and shoot both, and frankly I prefer the DI guns...cleaning be damned.




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[Joe Mamma]

Because the PWS system uses a operating rod attached to the top of the carrier with cheap YFS brand screws.

A lot of people don't like YFS simply because they are made in Taiwan (and not the United States), and people incorrectly assume Asian things are poor quality. But I have used YFS screws in DI and piston guns, and they have always been fine. In my opinion, they are actually at least good quality threaded fasteners, and maybe even very high quality.

I've seen a lot of junk threaded fasteners in my life, and none have been YFS.

When I hear people badmouth YFS screws, it reminds me of people who didn't like Gearwrench brand wrenches back in the day because they were made in Taiwan. Eventually people realized they were very high quality.

One benefit about having YFS brand screws is that you at least know the source/manufacturer of the screw. The generic no name stuff out there always makes me nervous. I often check the DI gas key screws on ARs I come across. YFS screws may actually be the most common DI gas key screws out there currently.

Joe Mamma

[Arctic1]

@MistWolf:

The thread was actually here, where the temp differences were measured across 4 different platforms:

https://www.m4carbine.net/showthread...-detailed-look

[scottryan]

A lot of people don't like YFS simply because they are made in Taiwan (and not the United States), and people incorrectly assume Asian things are poor quality. But I have used YFS screws in DI and piston guns, and they have always been fine. In my opinion, they are actually at least good quality threaded fasteners, and maybe even very high quality.

I've seen a lot of junk threaded fasteners in my life, and none have been YFS.

When I hear people badmouth YFS screws, it reminds me of people who didn't like Gearwrench brand wrenches back in the day because they were made in Taiwan. Eventually people realized they were very high quality.

One benefit about having YFS brand screws is that you at least know the source/manufacturer of the screw. The generic no name stuff out there always makes me nervous. I often check the DI gas key screws on ARs I come across. YFS screws may actually be the most common DI gas key screws out there currently.

Joe Mamma

YFS fasteners are banned in most aerospace applications and anything else that matters.

And I have never seen YFS fasteners used on any Colt, BCM, KAC, or LMT bolt carrier group.

[Joe Mamma]

I'm seeing a strawman appear here regarding the cleanliness issue, and interestingly enough I'm also seeing some take on advocacy for the strawman after the fact. This seems futile to me - I can't think of any trends in AARs from classes, the field or the range which have either system failing *with* proper lube strictly due to gas related fouling which would be exclusive of the other of the two systems. That is to say, there are just too few circumstances where one would be found saying, "if only I had been running the other system, my weapon wouldn't have failed due to this gas-related fouling." Being clean isn't an issue at all, but it seems like that is exactly where this discussion has fallen.

I will disagree with you slightly. Cleanliness is somewhat important to me. I normally like my trigger/sear/hammer contact areas well lubed. It can change the feel of the trigger significantly. At least some piston AR guns can stay well lubed much longer than the typical DI AR gun.

Also, when I do clean my guns, it is often much easier and quicker to clean a piston AR gun. I like DI AR guns, but there are significant differences (to me) in both types.

There are some people who shoot DI guns suppressed, and their guns get noticeably dirtier in the trigger/hammer/bolt areas when you compare the areas with and without suppressor use. With at least some suppressed piston AR guns, they do not really get dirty in those areas.

Joe Mamma