AK short stroke gas system

[ndh87]

Has anyone ever made a short stroke gas system for the AK? Something similar to an FAL gas system maybe? What if any advantages would a system like that offer over the regular setup?

 

[Omnivore]

The only conceivable advantage would be that the receiver could be slightly shorter. Otherwise, there are nothing but disadvantages.

 

[JesseL]

The AK already uses a short stroke gas system, so I'm not quite sure what you're asking?

 

[iamkris]

What he said

Gas systems
There are four principal types of gas operation: short-stroke, long-stroke, gas trap, and direct impingement.

A short-stroke gas system is defined as one which uses high pressure gas from the middle portion of the barrel that impinges on the piston head for a short period of time before excess gas is either cut-off (M14) or vented (AK-47) or the piston head reaches a stop (M1 Carbine). The distance the piston travels under pressure is generally less than its diameter.[2] The piston may or may not be attached to the bolt carrier. This is the most common type of gas operation.

A long-stroke gas system is generally defined as one which the stroke of the piston under pressure is greater than its diameter.[3] Because of the greater dwell time, gas must be ported from the barrel very near the muzzle of the weapon as in the M1 Garand. This relatively lower pressure gas acts over a longer period of time to impart the same amount of energy to the operating system. Because the operating parts are longer, they are necessarily heavier and this system is not used in modern weapons.

A gas trap system is similar to long-stroke operation, however gas is 'trapped' after leaving the muzzle. The "Bang" rifle and early "gas trap Garand" rifles use this system. The German MG-42 machinegun and other recoil operated weapons use this energy in combination with recoil energy for more reliable and energetic operation of the weapon. The gas trap system is also obsolete.

The direct impingement method of operation vents gas through a tube to the working parts of a rifle where they directly impinge on either the bolt itself as in the M16 rifle, or the bolt carrier proper.

Misconceptions
The terms short-stroke and long-stroke are often confused by both laymen and experts. The stroke is that portion of time when combustion gases contact the piston head prior to venting. It is not the total length the piston head might travel during the cycling of the action. The commonly reported misconception is that a piston being rigidly affixed to the bolt carrier is what constitutes a long-stroke system. The AK-47 is commonly referred to as a long-stroke action while the Armalite AR-18 is often used as an example of a short-stroke system. In fact, the stroke is virtually the same and the gas port is in nearly the same location along the barrel for both rifles. [4]

 

[Evil Monkey]

AAAAAAAAHHHHHHH!!!!!!!!

That post defies what I have learned over the years!

I refuse to believe that junk.

AK47, SIG550, etc, uses a long stroke, and AR18, FAL, etc, use a short stroke system.

 

[MMcfpd]

Now I'm confused. Kris, where'd your quote come from?

 

[Hoppy590]

wow. that just rocked my world.

im awaiting a follow up explination ( hopefully with visual examples)

 

[JesseL]

Here is a picture of an AK piston in its forward position, and another picture show how far back it travels before the gas is vented. All motion past this point is driven solely by inertia as the gas pressure as been relieved by the vent holes.

The AK gas-tube really isn't a gas-tube at all. It serves mainly as a guard and guide for the piston.

 

[Evil Monkey]

WHAT!?

I thought the gas pushes the piston and bolt carrier all the way. You mean to tell me that the gas only pushes the piston an inch and the entire piston and bolt carrier start flying backwards!?

If that's the case, then I really underestimated the power of gun powder.

So the gas isn't really pushing the piston, rather it's punching the living daylights out of the piston?

 

[Hoppy590]

i know where the vents are in an AK tube. but i have the feeling the AK would not operate the same with out the tube. i imagine the tube creates that extra PSI to reliably function the AK. the vent is very small for the amount of pressure introduced to the tube. i cant believe it all vents out those little holes and the rest of the tube is useless again. this is all speculation. so some one show me why im wrong

added: to say the piston is no longer effected by the gas after the valve is open. s like saying the round in no longer effected after it passes the hole for the gas operation. there still is pressure, albeit decreasing pressure, that operates on both the round and the piston

 

[JesseL]

Other short stroke gas systems work perfectly reliably with only a fraction of an inch of gas propelled motion from their separate, captive pistons. I don't see whats so unbelievable about the AK doing the same.

Not only that, have you seen what a loose fit the piston has within the gas tube? If there were any significant pressure acting on the piston by the time it was back in the tube, it would probably blow past the piston and blow the dust cover off.

 

[Hoppy590]

bear with me, im a paintball kid. grew up playing paintball. LOTS of experience with CO2, HPA and other compressed gasses. along with shop type experiance so i know that even 1 PSI can have effect. so im just posting questions here. im not doubting. i have no right to doubt. i just want to get things clear, know what i mean?

 

[JesseL]

added: to say the piston is no longer effected by the gas after the valve is open. s like saying the round in no longer effected after it passes the hole for the gas operation. there still is pressure, albeit decreasing pressure, that operates on both the round and the piston

What you're forgetting (and I neglected to mention) is that by the time the piston has reached the vents the bullet is leaving the barrel, at that point the pressure is very negligible.

 

[heypete]

I thought the gas pushes the piston and bolt carrier all the way. You mean to tell me that the gas only pushes the piston an inch and the entire piston and bolt carrier start flying backwards!?

Yup.

The SKS does a similar thing, but the stroke of the piston is a bit longer, but not by much.

Remember, that the gases in the barrel are under tens of thousands of pounds of pressure per square inch, and are able to propel a ~125 grain bullet at thousands of feet per second. That pressure applied to a heavier piston would certainly get it to move quite quickly.

Gun powder is very energetic indeed.

 

[fvf]

In my Chinese AK, the gas tube has 8 small holes on the gas tube. 2 4-rows on the front part of the gas tube. Yours seems to have 4 holes around where the gas tube is connected.

 

[50caliber123]

I thought a long stroke piston was a piston attached to the bolt (AK) and a short stroke piston struck a piston extension (SKS).

 

[BigG]

Regardless of what you call it, the difference mainly is the piston is permanently attached to the bolt carrier on the AK, where the so-called short stroke is more akin to the M1 carbine style piston.

What the guy is asking is "would there be a way to make it work without the extra mass?" The Dragunov uses almost an identical mechanism to the AK except it has a piston that is unattached to the bolt carrier. The light piston hits a tappet rod a smack which drives the bolt carrier back. The upside is less reciprocating mass.

 

[sharkhunter2018]

http://www.lwrifles.com/tech.php

 

[JesseL]

I thought a long stroke piston was a piston attached to the bolt (AK) and a short stroke piston struck a piston extension (SKS).

Regardless of what you call it, the difference mainly is the piston is permanently attached to the bolt carrier on the AK, where the so-called short stroke is more akin to the M1 carbine style piston.

Popular (very popular it seems) misconception, but no. The difference is in how far the piston travels under pressure. Short dwell time, high pressure actuation vs. long dwell time, lower pressure actuation. Swift kick vs. gentle push.

Claiming that the difference lies in the attachment of the gas piston is akin to claiming the difference between diesel and gasoline engines is the connecting rods.

Edit:
I wanted to add, I just tried my AK without the gas tube and it functioned flawlessly . I did have to be careful in how I held it so as not to give myself a blast of gas to the face

This confirms that the AK's piston is only propelled by gas for a short distance and the rest of it's travel is pure inertia. The 'gas tube' is in fact just a cover and guide for the piston.

 

[BigG]

I was born at night, but not last night -

A long-stroke gas system is generally defined as one which the stroke of the piston under pressure is greater than its diameter.[3]

I'm sorry to be a wet blanket, but whoever wrote the Wikipedia article you quoted referenced an article on internal combustion engines - for I believe a Sunbeam, a certain authority on automotive engines and of course, directly applicable to firearms discussions (insert irony here). Here is the reference they provided for the WIKI quote above :Sunbeam Tiger discussion of bore vs stroke

Below, the words that were somehow twisted by the Wikiwriter to pervert the minds of us firearms enthusiasts.

By definition, a short stroke engine has a bore that is greater than the stroke, while a long stroke engine has a stroke greater than the bore.

The correct firearms related reference appears to be this one: Discussion of long stroke vs short stroke as it relates to gas operation which I've helpfully quoted below -

The long-stroke design siphons off gas under somewhat low pressure via a port near the muzzle. The operating rod is fastened to the piston stem and extends all the way back to the receiver where it engages the breechblock or bolt. The short-stroke design takes its charge of high-pressure gas by means of a port only inches forward of the chamber. The operating rod is not attached to the piston stem; rather, it is mounted just behind it. The piston is driven violently to the rear where it hits the forward end of the operating rod. This blow drives the operating rod to the rear causing the same process of unlocking, extracting, ejecting, cocking, reloading, and locking as occurs in the long-stroke design.

 

[JesseL]

BigG:

The article you quoted is half-right.

Compare the locations of the gas port in an AK to the location of the gas port in an M1 Garand (everyone can agree the Garand is a long stroke system) and an AR-18 (everyone can agree the AR-18 is a short stroke system).

Which does the AK gas port location more resemble?

The way the gas piston is attached to the rifle and how it interfaces with the bolt carrier is not relevant to whether the system is long- or short-stroke.

Again, the difference lies in whether the bolt carrier receives a short, hard smack; or a long, gentle push.

 

[BigG]

The Wiki Article is flawed but not the source doc for note 4

The article I quoted is the same one that the Wikipedia article posted by IAMKRIS referenced.

I don't agree that whether or not the piston is attached to the bolt carrier is irrelevant to the name of the system.

An AK is considered a long stroke system, like a BAR M1918 or an M60 machinegun. The impulse to the piston in any of the current gas systems could be measured in milliseconds so duration of impetus is irrelevant.

What the guy who originally asked the question probably wants to know is how to reduce mass of reciprocating parts. An AK 47 has a huge mass reciprocating with the relatively small bolt. The extra mass probably helps reliability and that may be the reason they still build them with the so-called long stroke system.

Maybe the nomenclature as it exists does not meet your criteria but your explanation is not typical, and the fact that I agree with you in principle is irrelevant in this case.

it would make more sense to call it short impulse system vs long impulse system, but the current way is predicated on how far the piston itself has to travel. The dragunov uses a piston that just jumps back a 1/4" or so driving a long tappet rod that impacts the bolt carrier. That is a true short stoke, even tho it taps the gas down at the same place as an AK or M16.

 

[JesseL]

The impulse to the piston in any of the current gas systems could be measured in milliseconds so duration of impetus is irrelevant.

Milliseconds make a world of difference in all kinds of places. Ask anyone who's bent an oprod in their Garand by using too slow a powder.

 

[BigG]

Current gas systems means something post 1930s. Garand could be called the "first workable system." Kind of like the Model T Ford was the first mass produced automobile.

 

[ndh87]

Oh man...look what i started


I always understood that in a short stroke gas system the gas piston and bolt carrier were not connected. What i had in mind was a system where the gas drives the piston into the bolt carrier and just gives it a "tap", letting the inertia of the bolt carrier do the rest.

Something like this is what i had in mind

[/IMG]

http://www.lwrifles.com/tech.php