OK, OK, enough with the jokes. What's the difference between these two? I can venture some guesses but only guesses.
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OK, OK, enough with the jokes. What's the difference between these two? I can venture some guesses but only guesses.
Did I see some advertising, about the long stroke being less likely to cause carrier tilt/buffer tube 'erosion?' NOT saying it's true, but I thought I saw some aftermarket piston company tout their wares thusly...
Short Stroke: The piston travels less than the length of the cartridge.
Long Stroke: The piston travels more than the length of the cartridge.
Rule of Thumb: If the piston is attached to the operating rod or mechanism, it is a long stroke; if the piston is separate, it is a short stroke.
The definitions I was given are very similar to what KL Davis posted, but with this caveat:
Short Stroke- The piston travels a shorter distance than the length of the cartridge under power.
Long Stroke- The piston travels a distance longer than the length of the cartridge under power.
The AK is technically a short stroke piston, since the weapon vents gas and power to the stroke of the piston early in the extraction process.
Dang it. I should have looked first. You can find anything on that Wikipedia. Thanks all for the help.
Wow, I had always thought the AK was a LONG STROKE piston system.... ?
Does anyone know if there has ever been a long stroke gas piston AR, or "AR Variant", with the bolt/carrier attached to the op rod/piston?
Please I am not trying to be a smart a$$ can you tell me why my link to
http://en.wikipedia.org/wiki/Gas-operated_reloading
was sorely lacking of details compared to your definition I was just trying to give him a reference that I thought was relevant to his question.
I didnt write it the references to that page are at the bottom of the page.
Please I don't understand why you would say its sorely lacking in detail.:confused:
I thought the details where not great but they were just fine for his question.
Thomas-
I in no way meant to imply that you were to blame for the Wikipedia reference. Wikipedia is written by whoever chooses to take the time to do so. As such, it is not a solid reference since it is not reviewed by any authority.
Wikipedia constantly contradicts itself, which is rarely considered a good thing when it comes to references.
Now, to be clear, I am simply working from what I have been taught, and it has changed through the years.
Initially I was taught that long stroke versus short stroke was a simple matter of having the piston attached to the bolt carrier or not.
We were later told that the words "stroke" and "travel" are not synominous when it comes to piston operation. "Stroke" is when the piston is being pushed. "Travel" is simply how far the piston moves.
As such, according to the original definitions, the AK-74 has a long stroke gas piston, while under the second set of definitions it becomes a short stroke. I have absolutely no emotional attachment to any definition, and if either one is right I really couldn't be less bothered. While definitions are good for determining what a word means for brevity's sake, it really makes no difference in use, and far too much more effort is put into arguing about inconsequential things on the internet.
I would really like to have a firearms designer come in and settle the issue, prefereably with a reference of some kind.
Ok thank you Failure 2 Stop I see your point now. And I thank you for your response
about Wikipedia's deficiencies.
I can see both points in the AK gas system I also thought that the definition was how far the piston traveled thank you for informing me the difference between stroke and travel.
Thank you for your informative response
Also could you recommend any books that deal with that subject matter or any good books dealing with the AR in general?
Could you provide an example of a rifle with a long stroke piston design?
I'm most familar with the M14 and M1 Carbine, and they definitely have short strokes. I can't think of a single long stroke design, by this definition.
It occurs to me that the impulse of gas pressure is so brief that a long stroke design would be virtually impossible (or undesireably violent in terms of cycling speed).
Bimmer
The M1 Garand is a long stroke gas piston, and by the second set of definitions, is the most recent long stroke I know of.
The M14 combines aspects of the M1 Carbine tappet system and the M1 Garand, but the gas is cut off quickly so it is a short stroke.
Regardless, I am not a weapon designer. I don't know where firearms engineers go to school other than a gunsmiffin' course, but hopefully there is some authority on the matter that can settle the discussion.
Except a Garand isn't under pressure the entire stroke. Notice the short distance between the gas port and the muzzle. The gas can evacuate back into the bore in very short order.
Failure, the M14 is definitely a short-stroke system, because the length of the stroke is much less than the length of the cartridge.
I only have to think of the length of the tail of the piston (which is about how far the piston moves), and it's much shorter than a 7.62 cartridge.
Moreover, I think the gas system vents (and loses pressure) before the piston has even completed it's entire movement, so even less of that movement is the driven "stroke."
Heavy Metal's point about the Garand is exactly what I'm talking about.
Even if the piston moves with the op rod the whole length of the action, it's only "driven" for the first inch or so. After that it's inertia which keeps the op rod (and piston) moving rearwards.
If a piston were driven for a distance greater than the length of the cartridge, then it would still be driven when it stopped, and then the abrupt stop when the op rod or the bolt hits the receiver would be catastrophic (most gun designers don't want this at all). This is what bends and breaks op rods on M14s using reloads that are too hot.
So, I don't know anything, but I still can't think of an example of a "long stroke" piston design as you've defined it, which makes me think that there's something with the definition, if it's not applicable anywhere.
Bimmer
You should read the discussion page tab. Lots of discussion on short stroke, long stroke. To tell you the truth, most of us armchair types / laymen really don't need more then what the front page of Wikipedia offers up.Quote:
Originally Posted by Failure2Stop
I think Wikipedia gets a bad rap because it can and has been abused.
Guys-
I didn't coin the definitions, just going off of what mechanical engineers have said.
Talking with some of my friends in the industry have cast some doubt on the second set of definitions as they may be more closely related to internal combustion engines, which I am not qualified to do anything other than basic repair and maintenance. Anyway, by their definitions the power stroke length in relation to the piston diameter is the determining factor, apparently. If this was distorted into the "other" version of what is or is not a long or short stroke piston in a firearm and passed to us as "the real" definition, I don't know.
One of the problems with firearms is that common mechanical and physics terms are mis-applied or altered almost randomly it seems. It would really be nice to get the firearms industry on the same page as everyone else, or at least each other.
I barely know enough about cars and motorcycles to be dangerous, but for IC engines, this is correct.
Stroke longer than piston diameter is "long" (oversquare), stroke shorter than piston diameter is short ("undersquare").
I don't see how this could apply to gas guns, though, because all the ones I can think of have longer piston strokes than the piston diameter (though the M1 Carbine is close, if you count the fat base of the tappet).
Bimmer
People can geek out on this topic for weeks. Feelings will get hurt, personal insults will fly.
However, by way of consensus, if it works like an AK47. XCR, FNC, or SIG 556 it is commonly referred to as a long stroke piston
It works like an AR18, HK416, LWRC, and G36 it is commonly referred to as a short stroke piston.
Yup. It's sad how much people can get emotionally involved in someone else's definitions, especially given the complete lack of difference in actual operation.
Whether or not the op-rod is attached to the bolt/carrier has very little to do with anything about keeping the gun running or shooting it.
I would still like to know how real firearms engineers classify piston operation- by power stroke length or by op-rod/piston attachment.
and
Personally it seems like some are trying to derive the LONG STROKE / SHORT STROKE definition from engine motor definition. After reading some of the arguments on the discussion page of Wikipedia under this subject, I came away with the conclusion that the firearms definition of short stroke / long stroke should be defined under firearms with no relation to engine motors definition.Quote:
Originally Posted by Failure2Stop
I think the definition for stroke for firearms should fall under the length at which the piston is under power. I do agree now with your statement above that would make the AK47 a short stroke because it vents the gas early.
I am not a firearms engineer, and I didn't say at the Holiday INN last night, though just my thoughts on reading the arguments from both sides.
This part of the discussion makes sense and I am guessing this is the way firearm designers / experts define short stroke / long stroke;
Guess my logical view above would be wrong; the Holiday Inn might have helped then :pQuote:
The purpose of teh vent holes in the AKM gas piston is actually for the removal of CARBON that the piston head scrapes off the inside of the gas tube. As the piston runs back and forth, it also scours the inside of the gas tube. Once the piston passeds the holes, some of teh gas pressure then seeks it's easiest path out, and escapes through those holes -- carrying carbon fouling with it. This means that Private Ivan doesn't need to scrape the inside of his gas tube, even when using low-grade cruddy ammo. Any additional fouling (such as excess oil) used on teh piston or gas tube will get blown out as well. This has the effect of keeping the gun running under heavy fouling, without significantly changing the cycle time.
The contrasting view that an AKM is a "short stroke" system becuase of thge length of time it is under pressure ignores the fact that the AK47 piston spends MORE time under gas pressure than the M1 Garand due to the positions of the gas ports. Or that the AK47 and AKM gas tubes (interchangeable) somehow change the entire operating system from long stroke to short stroke.
Long stroke is, and has always been, defined as the gas piston traveling the full length of teh rewquired operating stroke. It DOES NOT need to be under full pressure to do so -- and in fact, NO gas piston, not even the M1 Garand, is under full gas pressure for the full stroke of the operating cycle. If they were, the gun would suffer a complete case rupture on each and every round fired, as the BARREL is under full gas pressure until the bullet leaves -- at which point BOTH the barrel and gas system vent to ambient pressure together. The gas piston starts out under gas pressure, but finishes it's cycle via INERTIA.
This yields a long, relatively smooth cycle. Doesn't matter if the piston is attached -- if it is pushing the bolt group the whole way, the whole mass is moving together with the relatively high mass smoothing out the cycle.
Short stroke systems impart a short, sharp smack to the bolt group. It can involve a conventional gas piston that hits a tappet (operating rod) that may or may not be attached to the bolt carrier. For example, the SKS carbine. Or, it may have a short piston like the M1 Carbine tappet. Or, it may have a conventional length gas piston that has a stop that prevents it from cycling the full length of teh bolt group's minimum operating cycle. The piston must impart enough energy via IMPACT, noyt inertia, to carry the whole bolt group through cycle.
It produces a sharp, short, cycle. . . but (in the case of systems without a full length gas piston, like the M1 Carbine), involves less mass cycling -- which can reduce felt recoil or weapon disturbance.
There IS a difference in how these two systems function, and the length of stroke is part of that. It is the physics of inertia, not gas pressure time, that defines short stroke versus long stroke. The definitions AS USED BY ORDNANCE DESIGNERS have been clearly set for over half a century. It was clearly understood that a long-stroke gas system moved the necessary operating stroke, and teh short stroke gas system did not, and that was the difference.
Or at least it was before Internet Experts decided to re-write the definitions on Wikipedia instead of using the actual textbooks on the subject that have stood for decades. But then, given the price and rariety of such basic texts as "Principles of Firearms" by Major Charles Balleisen (used as a primary source by Britannica, used as a textbook for the US Army Ordnance Corps, and later rewritten into an Army Technical Manual) and the five volume "The Machine Gun" series by Colonel George Chinn (written for the US Navy Bureau of Ordnance beginning in 1951 and continued through 1987, entire volumes were classified for decades), it isn't surprising that these fallacies persist. (These, along with the basic mechanical engineering texts, are the books the working military small arms designers reference when they are figuring something out concerning gun actions.) Few people have $1100 or so for those six books. Military small arms design engineering is a rather small field, so most of the good books have been out of print for 30-50 years or so. Instead, we get "experts" quoting from automotive repair manuals and using God-Only-Knows as their sources for these new and mechanically useless "definitions".
Defining short and long stroke systems based on the relative length of the cylinder versus it's width is appropriate for a Buick, but not a Kalashnikov. Trying to claim that an AR18 and an AKM are "exactly the same" and they are both "short stroke" is voodoo engineering not recognized by working ordnance designers.
For example, Eugene Stoner developed rifles with all three major gas systems -- direct impingement (AR15), short stroke gas (AR18), and long stroke gas (Stoner 63). He never had any problems differenciating between the three systems, and agreed that they all were valid (as opposed to saying the long stroke system was obsolete). The Russians have no problem differenciating between "long stroke" and "short stroke" based on whether or not the piston cycles the length of the minimum operating stroke. - - Geodkyt