DI or Piston?

[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.

The "bans" may simply be based on the country of origin (i.e., not U.S.) in at least most cases. I also have not seen them on Colt, BCM or LMT products. I don't think I've ever checked KAC's screws.

The biggest practical difference to me is that YFS gas key screws do not have the sharp full top edge that a true mil-spec gas key screw has. That edge helps keep it tight when staked properly. I still think they are quality threaded fasteners.

Joe Mamma

[Leuthas]

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.

If you aren't arguing those points - that the heat and fouling are a specific disadvantage of the "di" system - than what are you arguing?

[Arctic1]

If you aren't arguing those points - that the heat and fouling are a specific disadvantage of the "di" system - than what are you arguing?

I have never ever stated that they are a disadvantage of the DI system. I have never been critical of the DI system at all, regardless of forum.

I am stating that it is a fact that the internals of a piston guns run cooler and cleaner than a DI system - which MistWolf is arguing isn't the case.

[Leuthas]

I have never ever stated that they are a disadvantage of the DI system. I have never been critical of the DI system at all, regardless of forum.

I am stating that it is a fact that the internals of a piston guns run cooler and cleaner than a DI system - which MistWolf is arguing isn't the case.

Okay I misunderstood, perhaps I attributed another's words to you. I apologize.

With that said, though I can't speak for Mist, I don't think he's made the claim the the bolt, Carrier and other mechanisms inside the receiver of these weapons don't run much cooler in than external piston design. Everything I've read from him simply lays out the idea (though with some notable vigor) that cleaning of the gas block of a piston gun is much more crucial and necessary than the gas block of a "di" gun, which is true. The way in which the intensities or time consumption of the two compare is of course debatable, but he makes a valid point in emphasizing that the gas block becomes a major point of concern for cleaning in an external piston gun.

Personally I've found this to be true with my experiences of LMTs piston system. It wasn't as annoying as cleaning out the grooves of an upper or inside the trigger mechanism, but it is a significant focus I don't have with the traditionAL stoner design.

I'd just like to avoid senseless debate stemming from confusion.

[Arctic1]

Concur on avoiding confusion.

I think the main issue with "external pistons designs" is that there is not a single industry standard, that everyone follows. You have several different manufacturers with their own take on the design.
This in turn leads to less aftermarket support in terms of handguards, gas systems, barrels etc. The HK, for example, is not compatible with many triggers due to the need for a taller hammer to disengage the FP safety.

And as I noted in a previous post, retro-fit kits to put on a DI guns are several kinds of stupid - if one goes the piston AR route, go with one of the brands that designed them that way.

Most of my experience is with the HK guns, and there is next to no fouling in the gas block, the piston runs very clean although minor build up can occur near the tip. It is likely that there will be differences between the designs.

Also, as I have stated in previous discussions on this topic, my main concern (in a professional setting) when it comes to reliability issues is not from carbon fouling, but environmentals.

[MistWolf]

To be clear, I didn't claim the carrier and the bolt of a standard AR is as cool as an AR with a gas block piston. What I said was that the gas is carrying less heat when it gets to the carrier because it dumps heat as it passes through the gas tube.

When the piston is relocated to the gas block, the gas has more heat, the surface of the piston face is smaller and it's inside the gas block which gets much hotter than this carrier does. The piston in the gas block gets hotter than the piston in the carrier.

The bolt, which the back half of is the piston, does get soaked from being in the barrel extension, but in my experience, it didn't get as bit as the gas block.

I can also tell you that pistons in the gas block get quite hot! I've had to disassemble a FAL after it'd been shot a few times and the gas plug, block and piston couldn't be handled without gloves.

It's also my experience that properly controlling the gas flow of a standard AR does much to reduce the fouling in the receivers. Add a suppressor to the mix and the art will get pretty dirty, even if you dial the gas flow down.

When the piston is in the gas block, that's where the rifle will dump most of its fouling. Hard carbon will build up the face of the piston. Hard carbon will build up on the piston of a standard AR. A standard AR piston has the advantage of being easy to lube. Lube helps to keep the fouling soft.

People have various opinions if a gas piston should be in the carrier or in the gas block based on advertising claims or bad logic trains. There are only two reasons why I prefer a standard AR gas system over the HK gas block piston system-

- the standard AR gas system costs less
- I am more experienced (and therefore more comfortable) tuning a standard AR gas system to compensate for overly large gas ports and the addition of a suppressor

If I had a problem with properly designed gas block piston systems, I wouldn't bother with Garands, M14s, M1 carbines or the trouble of torquing and aligning FAL barrels to their receivers. I'd just shoot ARs

[Arctic1]

When the piston is in the gas block, that's where the rifle will dump most of its fouling. Hard carbon will build up the face of the piston. Hard carbon will build up on the piston of a standard AR. A standard AR piston has the advantage of being easy to lube. Lube helps to keep the fouling soft.

When the piston is relocated to the gas block, the gas has more heat, the surface of the piston face is smaller and it's inside the gas block which gets much hotter than this carrier does. The piston in the gas block gets hotter than the piston in the carrier.

On the HK design, there is no room inside the gas block for carbon to be deposited. Most of the hot gases are vented out of the front of the gasblock. Some gas escapes out of the rear of the gas block, as the piston moves rearward to push the piston rod back in order to unlock the BCG. This manifests as carbon build-up on the inside of the handguard in the area around the gas block. This has no bearing on the difficulty or ease of cleaning the weapon.

The piston on the HK is designed to withstand the heat that it is exposed to in the gas block. It is also supposed to be lubed. The only thing that wears on the piston are the gas rings. It gets discolored from the hot gases, and a minimal amount of carbon can build up on it, towards the tip. Cleaning the piston is a 1 minute job, at worst.

Edit to add photos:



This is from my old duty gun. This picture shows the piston the gun came with on the right, and a new one on the left. The discoloration is clearly visible. It had approx 10k on it. The only place where any carbon is visible, to the extent where you will get blackened fingers, is from the top ridge and down - ie the part of the piston that is not inside the gas block.

[MistWolf]

On the HK design, there is no room inside the gas block for carbon to be deposited. Most of the hot gases are vented out of the front of the gasblock. Some gas escapes out of the rear of the gas block, as the piston moves rearward to push the piston rod back in order to unlock the BCG. This manifests as carbon build-up on the inside of the handguard in the area around the gas block. This has no bearing on the difficulty or ease of cleaning the weapon

Surely, you aren't going to tell me the face of the piston will collect no carbon deposits. I'm not claiming the deposits will be excessive because they won't be. (The face of the piston is what you call the tip)

The only way that the deposits from the gas block have no bearing on ease of cleaning, is if those deposits are never cleaned. This is not the same thing as me claiming these deposits must be cleaned to keep the weapon functioning, because I'm not

The piston on the HK is designed to withstand the heat that it is exposed to in the gas block

You are right. If it wasn't, the HK would up and quit working. My reason for pointing out that the piston in the gas block is exposed to a higher level of heat is to counter the heat criticism leveled against the direct gas system. Critics of the direct gas system claim that directing hot gas against the piston in the carrier is a design flaw. Yet, they fail to realize that a piston in a gas block is not only exposed to hotter gasses, but also has less surface to deal with the heat and gets hotter. If a piston is more than capable of handling the heat in a gas block, it can handle the reduced heat found inside a carrier

It is also supposed to be lubed. The only thing that wears on the piston are the gas rings. It gets discolored from the hot gases, and a minimal amount of carbon can build up on it, towards the tip. Cleaning the piston is a 1 minute job, at worst.

From a fouling perspective, the gas rings give the HK an advantage over the FAL. The rings give a better seal and help wipe the fouling off the walls of the cylinder. The FAL uses no gas rings. Fit of the FAL piston in the gas block is critical and the piston can wear on hard use rifles

[Arctic1]

I can only suggest that you seek out the opportunity to educate yourself by trying one.

Not much more I say will have a better effect than that.

You are basically telling me that I don't know and understand a weapon that I carried on duty for several years, and currently own the civilian version of.
And this from a position of NEVER having shot one yourself.

[MistWolf]

I'm not sure what you're saying here. Are you suggesting an HK never has carbon fouling? How am I saying you don't understand your weapon?