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Posted: 2/3/2004 5:55:36 PM EDT
| Can someone explain how the gas tube on an AR works? I think I understand but would like some clarification and none of my manuals get that detailed. I am most interested in what happens at the end under the front sight. Thanks. |
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That is what I thought happened but I was having doubts because it seems like such a poor setup compared to a piston design like that of the AK variants. How dirty does the gas tube get? It would seem that since powder burn is so varied on all of the AR platforms and ammo brands, that the tube could get clogged with carbon deposits rather quickly. Or, does the gas tube not require cleaning? I would think that if the bore gets dirty, then the gas tube would as well. Especially where it meets the barrel. Lastly, how does this design keep from negatively affecting the bullet's travel down the bore? The abrupt redirection of gas flow seems like it would cause some odd things to happen to the bullet's velocity. |
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The gas tube does not normally require cleaning. The high-velocity, high-heat gases will blow out carbon and other deposits. As for the design itself, the AR15 series like all gas guns (AK47 included) will bleed off some of the gases to opperate the system. This will inevitably couse some velocity loss compared to like-lenghth non-ported barrels. But the loss is minimal in the big picture of things. Tex89 |
| the milatary has been using it for over 30 years i dont think you need to worry to much about it ...many people have never cleaned there gas tubes ...i dont think it would get dirtier from 30 rounds to 3000 rounds....like tex said it blows itself clean every shot....ive heard just put a drop or c l p in the tube every time you clean it that way it breaks up some of the powder film....i dont think its neccassary though..... |
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Quoted: [red]it seems like such[/red] a poor setup compared to a piston design like that of the AK variants. Hardly. The AR15 gas system uses fewer expensive parts, fewer machined parts and fewer moving parts. That means it costs less, carries easier, repairs cheaper, and wears slower. [yeah, that makes all the difference] |
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A lot of good info here. Thanks for the replies. Tweak, the next time you quote me, don't quote me out of context. You make it sound as if "seems" has been replaced with "is". No flames and no harm intended, just pointing out how it can be taken the wrong way if quoted incorrectly. ;) Sharpshot, I love your signature line, good for you! :D |
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I was told not to EVER bother cleaning the gas tube, by one of the senior firearms instructors at NRA HQ. Made sense to me, given what others are saying. (High speed hot gasses blowing through it.) He said that if you want to screw stuff up, go ahead and spray some gun scrubber or brake cleaner up in there, but otherwise to just let it alone. I haven't cleaned my gas tubes in over thousands of rounds, and I've experienced no decrease in reliability. I ran a pipe cleaner up one of them once, and it came out with absolutely nothing on it, so I figure there's nothing to worry about. |
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How do you think that AK piston is pushed back, Same hole in barrel venting gas and velocity away from the bullet, pushing the piston , rather than going back to the receiver and pushing on the bolt, it's the same system. For a minute I was going to chastise you for using the words AK, better, and accuracy in the same post. But you left out Accuracy because you obviously must have shot an AK before. |
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Quoted: basically once the bullet passes the front sight the explosion behind it is sent through the gas tube witch blows back your bolt carrier... there you go It doesn't end quite there. The expanding gasses actually flow into the carrier and actually blow the bolt forward, unloading the stress on the locking lugs (that's what those little piston ring thingys are for) as it pushes the bolt carrier back. Makes for a very robust action. |
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Quoted: Quoted: basically once the bullet passes the front sight the explosion behind it is sent through the gas tube witch blows back your bolt carrier... there you go It doesn't end quite there. The expanding gasses actually flow into the carrier and actually [red]blow the bolt forward,[/red][?] unloading the stress on the locking lugs (that's what those little piston ring thingys are for) as it pushes the bolt carrier back. Makes for a very robust action. im sorry but the only mechanical way a shell can be ejected is buy the GASSES BLOWING BACK THE [U]BOLT CARRIER[/U] THE [U]BOLT[/U] IS THEN TURNED BUY THE ANGLE CUT IN THE CARRIER UNLOADING THE STRESS<-----THAT IS HOW THE WHOLE THING WORKS .....the rings are for keeping the gases "burnt powder / resedue " contained in one place "sealed" so it shoots out the holes in the side of your carrier.....thank you.... [red]The bolt is all the way forward once the bolt and bolt carrier load a round it can not possibly blow it any more forward........[/red] |
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Quoted: Quoted: Quoted: basically once the bullet passes the front sight the explosion behind it is sent through the gas tube witch blows back your bolt carrier... there you go It doesn't end quite there. The expanding gasses actually flow into the carrier and actually [red]blow the bolt forward,[/red][?] unloading the stress on the locking lugs (that's what those little piston ring thingys are for) as it pushes the bolt carrier back. Makes for a very robust action. im sorry but the only mechanical way a shell can be ejected is buy the GASSES BLOWING BACK THE [U]BOLT CARRIER[/U] THE [U]BOLT[/U] IS THEN TURNED BUY THE ANGLE CUT IN THE CARRIER UNLOADING THE STRESS<-----THAT IS HOW THE WHOLE THING WORKS .....the rings are for keeping the gases "burnt powder / resedue " contained in one place "sealed" so it shoots out the holes in the side of your carrier.....thank you.... [red]The bolt is all the way forward once the bolt and bolt carrier load a round it can not possibly blow it any more forward........[/red] Umm, no. What keeps the bolt from blowing back at ignition? The force of the locking lugs perhaps? Ya think this force is greater at ignition than before? It's a simple law of physics, for every action there is and equal and opposite reaction. There is a chamber made by the bolt to the front and the carrier in which it fits. As the gas flows into this part of the bolt carrier it in fact does exert a forward pressure on the bolt, hence the name of the action, "direct inpingement". Yes the bolt carrier and the cammed groove in it, twist against the bolt cam pin to rotate the bolt but there is gas pressure with in the bolt carrier that does, to a lage extent, counter the rearward force of the gases in the barrel/chamber. As the carrier moves to the rear and because the bolt stays stationary, as the bolt begins to extend, the gas rings pass forward over the holes in the right side of the carrier, venting the gas. No, the bolt doesn't actually move forward, (not much anyway) but there is a substancial forward force on it during unlocking, hence the reduction of stresses on the lugs during unlocking. Take your bolt and carrier out and look through those little holes as you slowly pull the bolt in and out. The ejection is performed by the ejector which sits in the bolt face and ejects the spent case...or did you mean extract, but that is performed by the extracter. |
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Hi guys, my limited experience with firearms, rifles in particular, has led me to the firm belief that a gas operated rifle with a gas piston will be inherently less accurate and will have more parts that can fail. Most of us know in order to make a rifle shoot good everything must be consistent from shot to shot. With the piston, springs and usually the piston tube directly affixed to the barrel, sometimes it’s hard to get all those parts to agree all the time. With an AR the lockup of the bolt and barrel extension is always the same, add a floated barrel and a gas tube that is only affixed at one point, consistency from round to round is exceptional, especially for a military firearm. I have only built a few AR-15s and with the help from this forum all of them have been very easy. My last build was a FAL and with [url]FALfiles.com[/url] for a reference, getting the rifle together was also easy. Making the rifle dependable has been a completely different matter. The gas piston and the gas tube has been a step-by-step elimination of problems. Now, I understand I’ve not built but one FAL and I built it with used parts, but the entire aspect of the gas piston and all of the associated parts that make it work seems to be a waste of metal that could be used for another AR-15 barrel. With the dependability of the AK, it’s tough to argue it’s a poor system. But wouldn’t it suck to see a tango at 200 yards and you couldn’t hit it unless they started to move around. I find it tough to believe a tanker in the Soviet Army designed the AK. The Russians used the German MP44 {I know they say they didn’t} for a template and made with the best tooling available in the Soviet Union {+ or - .0200”} and you have the AK. Mix 14 years of time with precision manufacturing and lightweight alloys plus a really smart team and we have a rifle that has been in service 30+ years. My go to AR is a Bushy lower, barrel, bolt and bolt carrier that is over 5000 rds and I’ve never cleaned or put anything in my gas tube. With 12000+psi running to operate the action, there can’t be very much of anything left in there. If I put my AR up for a month or so I’ll make sure to pay a little more attention to the carrier key and bolt than I would usually. In regards to “direct impingement” I believe that a the term used to describe the operation of the AR, the gas is directly impinged on the bolt {in relation to the bolt carrier} instead of a piston, not the forward movement of the bolt to relieve stress on the bolt’s locking lugs. By the time a bullet has exited the barrel, the brass has contracted enough to be extracted, gas is pushing the carrier back unlocking the bolt and hopefully brass is flying out the ejection port. All of the gases directly impinge !everything! to the rear of the receiver. The gas rings keep the gases from going forward into and on the cam pin, extractor, ejector, bolt face and the rear of the locking lugs. When cleaning the bolt and carrier it’s easy to see the difference with the lack of carbon in front of the rings {chamber side} compared to behind the rings. Sorry for the long post. It’s late and I really like my AR. |
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Quoted: Hi guys, my limited experience with firearms, rifles in particular, has led me to the firm belief that a gas operated rifle with a gas piston will be inherently less accurate and will have more parts that can fail. Most of us know in order to make a rifle shoot good everything must be consistent from shot to shot. With the piston, springs and usually the piston tube directly affixed to the barrel, sometimes it’s hard to get all those parts to agree all the time. With an AR the lockup of the bolt and barrel extension is always the same, add a floated barrel and a gas tube that is only affixed at one point, consistency from round to round is exceptional, especially for a military firearm. What about the Daewoo K2 with a M-16 style bolt and carrier with a piston attached to it? Lockup is always the same and it sure is damn accurate for a piston driven system. It's as accurate as my Bushy and cleaner. |
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Quoted: In regards to “direct impingement” I believe that a the term used to describe the operation of the AR, the gas is directly impinged on the bolt {in relation to the bolt carrier} instead of a piston, not the forward movement of the bolt to relieve stress on the bolt’s locking lugs. By the time a bullet has exited the barrel, the brass has contracted enough to be extracted, gas is pushing the carrier back unlocking the bolt and hopefully brass is flying out the ejection port. All of the gases directly impinge !everything! to the rear of the receiver. The gas rings keep the gases from going forward into and on the cam pin, extractor, ejector, bolt face and the rear of the locking lugs. When cleaning the bolt and carrier it’s easy to see the difference with the lack of carbon in front of the rings {chamber side} compared to behind the rings. Sorry for the long post. It’s late and I really like my AR. Quoted: What about the Daewoo K2 with a M-16 style bolt and carrier with a piston attached to it? Lockup is always the same and it sure is damn accurate for a piston driven system. It's as accurate as my Bushy and cleaner. So what is the purpose of the gas key on the carrier porting gas into a chamber in the bolt carrier? Why not just a tube that would allow a stroke long enough to push the carrier back far enough to function? The tube on the key could extend forward out the front of the upper so gas could vent outside the action. |
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Hi Sulaco. I think it's a fair question because it's hard to believe that a puff of gas can operate a bolt so quickly and reliably. I'm facinated by these types of rifles for that reason. Understand that a military rifle can develop in excess of 50,000 psi in that barrel in less than blink of an eye. Some of that pressure is what is captured by the gas system and make these rifes work. The early military gas-operated rifles were introduced to the world by the russians with the SVT38 in 1938 and has been used by a number of military semi-autos from around the world. The 38, SVT 40, FAL, L1A1, SKS, AK series, FN49, and M1 Garand were all very similiar in that they used a gas piston to push the bolt back. Then, other contemporanious designs elminated the piston entirely and only gas was used to open the bolts in rifles including the French MAS 44, 49 & 49/56, Egyptian Hakim and Rashid, Swede AG42b, VZ52 and 52/57 (slightly different but similar). These designs all rely on gas to directly blow back the bolts. Once the bolt has been pushed back, the balance of the gas is expended and the bolts are all forced forward by the strong bolt spring, thus stripping off a new round ready to fire once again. So, the direct-gas system is a time-tested system. The direct gas system has an advantage because it has fewer parts than gas-piston systems such as found on the models I've first mentioned. The gas-piston systems have more moving parts which can get dirty and fail. In the direct-gas systems such as found on our ARs, as long as that gas tube is clear and the bolt can move, the direct gas system has got to be the most reliable and easy to maintain system ever designed. Most gas tubes are made from stainless steel to ensure reliability and resistance to fouling for this reason. Many of the early direct-gas and gas-piston operated rifles such as the ones I've previouly mentioned, have gas adjustment valves that were necessary because the ammunition was not as reliable or uniform. Early ammo was also not as clean as today. There is a huge difference in the performance of 7.62 x 54R ammo, for instance, depending on the country of manufacture. Here, a gas valve was very important as you had to tailor your rifle's gas system so it wouldn't destroy your rifle on one end or fail to operate the bolt on the other. As technology, reliability, and uniformity of the ammo improved with the likes of the 5.56 used by these AR rifles, the need to be able to adjust the gas flow because superfluous and, therefore, are no longer installed thus eliminating one more area for crud to build up and maintenence performed. I collect C&R semi-autos and am facinated by the subtle differences in each generation of semi-auto's gas systems. So far, the AR15/M16 is the slickest I've come across as it either works 100% or fails making repairs easy to identify. Thus it's the most reliable which is why I've seen very few posts here about feeding and firing failures compared to other forums for older, less sophisticated predecessor rifles. Just thought I'd contribute my 2cents. Rome |
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Quoted: So what is the purpose of the gas key on the carrier porting gas into a chamber in the bolt carrier? Why not just a tube that would allow a stroke long enough to push the carrier back far enough to function? The tube on the key could extend forward out the front of the upper so gas could vent outside the action. Quoted: What about the Daewoo K2 with a M-16 style bolt and carrier with a piston attached to it? Lockup is always the same and it sure is damn accurate for a piston driven system. It's as accurate as my Bushy and cleaner. With a millisecond pulse of gas, the bolt carrier is pushed back where it is retarded by the proper amount of tension from the buffer spring and the mass of the buffer. The small volume of gas is under extreme pressure and bled off behind the gas rings. It’s such a small volume, hundreds of rounds can be fired in a short amount of time and pose no problem. I agree the same gas that propels the bolt carrier to the rear of the upper pushes the bolt forward. The bolt is realigned for chambering the next round by this force. The operation of rotating the bolt to lock and unlock is driven completely by the cam pin. The entire operation is truly amazing. The reference to an external tube from the key is funny. Kind’a makes it hard to keep the gas tube in the right place. It’s great when any rifle will shoot as well as an AR. Ain’t it Fighter. Is this the standard for the Daewoo line or did you find a “good one”? My personal belief is, no other country in the world can produce the mass quantities of high-grade rifles that are required for the military. I know Fn makes them but we could if it wasn't for politics. Besides Stoner made it run. I’ve already noted the reliability of an AK style, yet if the AR was having problems with front line troops, we would hear about it for sure. I just saw the pictures of an MP44 being fired in Iraqi. There’s no doubt if the AR was screwing up this site would have the details. The only thing negative I’ve read is the lack of energy at extended range. Ranges the round isn’t designed for. I feel there is a perception where deadly force with a rifle is viewed as something that happens at 700 yards with two persons standing, slung in a jacket and watching the wind. I’ve never been hit with a 55 grain round moving at 2000 fps. [mv. 3100 fps. Impact range 300 yds.] But I’d have to say it would hurt. Standard issue 20” barrel. I’ve read the discussions about the need for a new larger round. If the 5.56 was bumped up 200 fps at the muzzle, which could be done, things would be good. Late……..[|)] |
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Quoted: .... I agree the same gas that propels the bolt carrier to the rear of the upper pushes the bolt forward. The bolt is realigned for chambering the next round by this force. The operation of rotating the bolt to lock and unlock is driven completely by the cam pin. The entire operation is truly amazing. Thanks mark. I'll try a little experiment tonight. I'll take an old piece of gas tube and stick it in a bolt/bolt carrier, set it on the table and then blast some air down the gas tube. I'll see whether the pressure pushes the bolt out of the carrier and note how far the carrier moves back, just kind of an indication as to how much force is exerted on the bolt relative to it's weight to that of the bolt carrier. .... The reference to an external tube from the key is funny. Kind’a makes it hard to keep the gas tube in the right place. I believe Olympic makes and upper and so does someone else like this, gas tube and piston out the front of the reciever. It's the ones that make a side folder AR15. Can't think of their name right now but there was a movement for a group purchase for uppers awhile ago. Edited to add; I'm not familiar with the function of these types of actions so I'm not sure weather they use the expansion chamber in the bolt carrier or not. |
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Quoted: I believe Olympic makes and upper and so does someone else like this, gas tube and piston out the front of the reciever. It's the ones that make a side folder AR15. The Olympic Arms OA series uses the standard gas system. It's the buffer tube that is over the barrel. OAI also made a gas piston 10mm upper for awhile. The Z-M Weapons line use an op rod. |
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Quoted: With the dependability of the AK, it’s tough to argue it’s a poor system. But wouldn’t it suck to see a tango at 200 yards and you couldn’t hit it unless they started to move around. This myth has been adequately disspelled by the AK-74. The inaccuracy of the AK-47 and AKM had more to do with the round than anything else. The AK-74 can definitely hang with the AR in the accuracy department. |
| Yep, Half. You knew that, but a lot of guys forget it. There have been several attempts to convert the AR15 design to a piston design, such as the Rhino system some years ago. These kits had to work doubly hard, to not only move the bolt carrier back, but to unlock the bolt. Something to consider when guys start saying, "why don't they..." |
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With the input from members I hold in the highest respect, I cannot lend my beliefs of the operating system of the AR as described in the previous posts. While I agree the gas operation of the AR has a function of moving the bolt, I do not believe it relieves stress on the locking lugs. Regardless of what the designer or manufacturer stated, which could be a good sales point to people who don’t look close. The mechanical operation of the cam pin driven by the kinetic energy from the bolt carrier will bring much greater force to bear on the bolt before the pneumatic operation at this point of the cycle of the Stoner design. With the bolt moving back from the initial blast of gas it is already activating the cam pin unlocking the bolt. The residual bleed off of gas repositions the bolt for proper reengagement of the locking lugs, where it is locked once again by the forward movement of the bolt carrier operating the cam pin. What the hell, I’ve only built a few ARs. They run 100%. The philosophy aspect is something I shouldn’t fool with. Nuts and bolts, that’s what I’m happy with.[beer] |
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