AR- Piston or Direct Impingement?

[Gun]

But his design that went on to be successful is the inline piston of the AR

The design of Stoner has the bolt carrier housing doing the work, as a moving
cylinder. The bolt (piston) is initially stationary. The bolt in Stoner’s design
doesn’t make the same comparison to the actuating rod (piston) in a gas-piston
system, which does move and influences the action of the bolt carrier group.

If the actuating rod were attached to the bolt carrier housing, then this could still
be considered an expanding gas system, for how else would the actuating rod move.

[MistWolf]

The design of Stoner has the bolt carrier housing doing the work, as a moving
cylinder. The bolt (piston) is initially stationary.

That was well established in the first post of this thread

The bolt in Stoner’s design doesn’t make the same comparison to the actuating rod (piston) in a gas-piston system, which does move and influences the action of the bolt carrier group.

I do not understand what you're trying to say here. Using an actuating rod, either as part of the piston or as a separate part, necessitates it being place offset to the bore and bolt. By eliminating the actuator rod and integrating the piston with the bolt, it brings all the recoil forces inline with the bore and to reduce muzzle rise

If the actuating rod were attached to the bolt carrier housing, then this could still be considered an expanding gas system, for how else would the actuating rod move.

Eugene Stoner didn't see it this way as he describes his system as being an expanding gas system in the original patent. I believe what makes a system an expanding gas system is the fact that the gas uses a chamber that expands in volume as the gas pressurizes it. The AR cylinder inside the carrier is such a chamber. (Note that the AR piston remains inside the cylinder unlike the Ljungman.) Whether a system uses an actuator rod or not has nothing to do with it

[Freedoooom]

Whole lot of crazy.

You have essentially for an example argued that coal turbine actually is just the same exact thing as a hydroelectric turbine and anyone who tells you coal turbine runs hotter is just crazy.

No its not. They completely two different principles of how to cycle a gun. One uses the forces of hot gasses inside the chamber, one uses it under a hand guard to push a rod.

There is no debate whether a piston system runs cleaner and cooler. Its just a fact, of physics and empirical evidence. Your own post even points to this, it not only blows hot gas into a key, it blows it into the bolt it self, which also blows gas out through out the whole chamber.

[SpaceWrangler]

I'm pretty sure you'll find it doesn't blow gas into the chamber.

[seabyrd6]

Whole lot of crazy.

You have essentially for an example argued that coal turbine actually is just the same exact thing as a hydroelectric turbine and anyone who tells you coal turbine runs hotter is just crazy.

No its not. They completely two different principles of how to cycle a gun. One uses the forces of hot gasses inside the chamber, one uses it under a hand guard to push a rod.

There is no debate whether a piston system runs cleaner and cooler. Its just a fact, of physics and empirical evidence. Your own post even points to this, it not only blows hot gas into a key, it blows it into the bolt it self, which also blows gas out through out the whole chamber.

From what I understand the gas port on DI guns will expand and wear due to the backup of pressure at that point, whereas with the piston system, it reduces the back pressure more quickly and helps save the port- but the return argument is this- who is going to shoot that many rounds- some people have and why not just admit we don't drive model T's anymore and there are many improvements in all aspects of weaponry- you know GS might have taken a likin to the piston but his heart wore out- Thanks, CB

[MistWolf]

Whole lot of crazy.

You have essentially for an example argued that coal turbine actually is just the same exact thing as a hydroelectric turbine and anyone who tells you coal turbine runs hotter is just crazy.

No its not. They completely two different principles of how to cycle a gun. One uses the forces of hot gasses inside the chamber, one uses it under a hand guard to push a rod.

There is no debate whether a piston system runs cleaner and cooler. Its just a fact, of physics and empirical evidence. Your own post even points to this, it not only blows hot gas into a key, it blows it into the bolt it self, which also blows gas out through out the whole chamber.

I see what you're trying to say. However, there are assumptions behind your premise. You are assuming their is significant difference in heat between the inline system and the offset system. What are the actual temperature differences of the BCG when shooting 200 rounds of ammo in an offset upper compared to an inline upper? How many BTUs of heat are actually carried into the expansion chamber of the carrier with each shot? How much hotter does the gas block of an offset piston upper get compared to the inline piston upper? Does that extra heat contribute to port erosion? Does it add to barrel heat? Will it make the handguards hotter affecting shooter's ability to handle the rifle? How much carbon build up can the piston and cylinder of the offset upper take before it impacts function?

Where is the empirical data? Show me the physics. I'm still searching for these answers.

Also, you may want to re-think your example. While the coal turbine and hydroelectric turbine both generate electricity, they are different technologies utilizing completely different power sources

[Battle*Hound]

LMT MRP Piston Uppers = YUMMM

[jonconsiglio]

SNIP

LMT has a piston system because they sell and customers were asking, not because they think it's necessary. I think it's pretty obvious why Colt has a piston coming.

I have two SCARs that see a lot of use. I've owned a couple piston ARs but prefer DI and currently run all DI ARs. I've used them in all typed of environments and pushed them very hard, gotten them filthy and ran all types of ammo. The piston does nothing truly better than my ARs unless we're talking SBRs (on the extreme end) or suppressed full auto fire. For most all normal use, including military use, the AR with it's DI system is perfectly acceptable.

As to why other rifles aren't using it, I have no idea. I just know what works. I'm all for advancements in the industry if they are truly better. If they're just a different way of doing things at an increased cost with very little benefit, I don't see it as a great idea or worth the extra cost.

[Arctic1]

Just a quick observation regarding specific tolerances of the M4/M16 FOW when it comes to fouling, since reliability came up.

When browsing the MIL-SPEC for the M193 and M855, they have a requirement they need to pass in regards to fouling:

M193 (MIL-C9963 F):

3.12 Fouling. -The fouling accumulated In the weapon during the firing of 1000 sample cartridges shall not cause failure of the weapon to function.

http://www.everyspec.com/MIL-SPECS/M...C-9963F_25766/

M855 (MIL-C-63989A):

3.13 Fouling. The fouling accumulated in the M16A2 and M249 weapons during the firinq of the sample cartridges shall not cause failure of either weapon to function

NOTE 4 The sample for this test shall be the sample
specified for the Function and Casualty test for each respective
weapon, i.e. 800 rounds for the M249 and 800 rounds for the M16A2.

http://www.everyspec.com/MIL-SPECS/M...-63989A_37914/

Now, these spec's indicate that the weapon should function firing 4-5 times the normal combat load without failure, with these loads. It does not say anything about the lubing scheme used for the testing.

According to the MIL-DTL-71186A for the M4A1 Carbine, the Endurance test is 6000 rounds, and having to pass these requirements:

3.6.7 Endurance.

3.6.7.1 Endurance functioning. The weapon shall fire 6,000 rounds of M855, 5.56mm ball cartridge in accordance with drawing 9342868. There shall be no more than the number of malfunctions and unserviceable parts allowed in Table I.

Table I:

4.5.7.1 Endurance functioning. Each weapon shall be fired in accordance with the Operator’s Manual 9-1005-319-10 and shall be held in a firing stand simulating shoulder firing in accordance with drawing 11837945 (auto firing), using ammunition M855, 5.56mm ball cartridges in accordance with drawing 9342868.

a. Firing procedure. Firing shall be accomplished in 50 cycles using 30
round magazines. One (1) firing cycle shall be as specified in Table V.
Cooling of the barrel shall be to the point that it is capable of being held by the bare hand. Supplemental cooling is permissible in the hand guard area.

b. Cleaning and lubrication. Weapons shall be cleaned and lubricated at the beginning of the test and at the end of every 10 cycles. Weapons shall be lubricated after the fifth cycle and at every 10 cycle increment. No other cleaning and lubrication shall be performed during this test. At the close of each day's firing, the weapon shall be protected against corrosion.

i. Lubrication. Weapons shall have been lubricated using lubricant
in accordance with MIL-PRF-63460. Apply a light coat of oil to
all surfaces of the bolt carrier group. (Do not apply excessive oil
in the bolt firing pin recess.) Apply a moderate coat of oil on all
firing mechanism components in lower receiver.

http://www.everyspec.com/MIL-SPECS/M...-71186A_30742/

It is quite clear that the tolerance levels are quite good, in my opinion. I do not understand why there has to be so much contention between DI and Short Stroke Piston systems.

If your weapon and ammunition combination can pass the requirements documented in the mil-spec's provided here, I would say that all is well. M855 must not cause a failure to function in 800 rounds (M16A2). That is 2/3 of total rounds fired in the course of 10 firing cycles fired before relube and cleaning.

I tried searching, but could not find the equivalent document for the HK416 (Short Stroke Piston). Probably because it is SOF issue, thus not being publicly available. Therefore I cannot say if testing requirements are the same or more rigorous.

Like I said, if your weapon can pass the specs shown in my reply, you are probably good to go.

[Thomas M-4]

[QUOTE=Koshinn;1230447 Why didn't HK utilize it in the XM8? Or FN with the SCAR? QUOTE]
Those are techincaly called gas tappet systems. They differ from conventional short stroke operating systems the piston is contained in the gas block and there is not a sperate operating rod its actully part of the BCG.