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AR Gas/DI explanation
- Thread starter gizmo688
- Start date
Wow, lots of misinformation here.
DI is piston, it's on the tail of the bolt - for those of you either more nearsighted than me, or simply in denial, it's right there where the GAS RINGS are installed.
Stoner simply moved it inside the carrier to make the forces coaxial. Offset operating rod designs do have to compensate for carrier tilt, the designers added rails for the bolt to ride on to control it.
DI is not dirtier than any other self loading gas action. Once the case is loose enough to extract, the gas pressure flows back around it into the action. Plenty of pics of 10,000 rounds thru AK's with dirty bolts on the internet, much less just ask any HK91 owner. No gas action at all, and mine seemed to get filthy in one magazine.
Piston to piston, both get dirty. It doesn't take very long to shotgun an AR to get to the piston and clean it - if you bother. It does take longer to take down handguards or a quadrail to get to the piston on those guns, why some think a DI takes longer escapes me. Ignorance or denial.
I wasn't any fanboy of the little poodleshooter in the beginning, I bought .30's to do a man's work. Once I got away from the Army I could independently reflect on it, and studied up on forums across the internet. I became clear that just because we own firearms doesn't mean we know squat about design and engineering. Much like the Chevy fans who think their Brand is annointed, they live in complete ignorance of it's compromises and defects. Because of that, they can't rise above the mundane.
Stoner did a lot more than just move the piston into the carrier and lose the inefficient mechanical op rod concept. He also incorporated the barrel extension, which the bolt locks into, NOT the receiver. That makes the upper and lower non-stressed parts as far as the chamber is concerned, and exactly why newer designs can use polymer lowers and extruded uppers. The barrel nut allows it to be a free float when equipped, but that's actually unnecessary as combat accuracy is easily achieved without it. And he put all the controls readily to hand, making it the minimum ergonomic standard for all combat firearms since.
Most just look to some very short term fielding problems that occurred for a few months back in 1968, all of which were based on compromises degrading the original design, not because of it. Stoner didn't delete chrome plating, didn't specify reusing powder, didn't state the gun never needed cleaning, didn't delay shipping cleaning kits, and didn't insist on putting on the forward assist. PISTON GUN FANBOYS DID, non-engineers who had no clue, who tinkered with the design and got people killed messing with it. Stoner vehemently objected, but by then COLT owned it and was bending over because "the Customer is always right."
And the customer proved to be dangerously ignorant.
DI is piston, it's on the tail of the bolt - for those of you either more nearsighted than me, or simply in denial, it's right there where the GAS RINGS are installed.
Stoner simply moved it inside the carrier to make the forces coaxial. Offset operating rod designs do have to compensate for carrier tilt, the designers added rails for the bolt to ride on to control it.
DI is not dirtier than any other self loading gas action. Once the case is loose enough to extract, the gas pressure flows back around it into the action. Plenty of pics of 10,000 rounds thru AK's with dirty bolts on the internet, much less just ask any HK91 owner. No gas action at all, and mine seemed to get filthy in one magazine.
Piston to piston, both get dirty. It doesn't take very long to shotgun an AR to get to the piston and clean it - if you bother. It does take longer to take down handguards or a quadrail to get to the piston on those guns, why some think a DI takes longer escapes me. Ignorance or denial.
I wasn't any fanboy of the little poodleshooter in the beginning, I bought .30's to do a man's work. Once I got away from the Army I could independently reflect on it, and studied up on forums across the internet. I became clear that just because we own firearms doesn't mean we know squat about design and engineering. Much like the Chevy fans who think their Brand is annointed, they live in complete ignorance of it's compromises and defects. Because of that, they can't rise above the mundane.
Stoner did a lot more than just move the piston into the carrier and lose the inefficient mechanical op rod concept. He also incorporated the barrel extension, which the bolt locks into, NOT the receiver. That makes the upper and lower non-stressed parts as far as the chamber is concerned, and exactly why newer designs can use polymer lowers and extruded uppers. The barrel nut allows it to be a free float when equipped, but that's actually unnecessary as combat accuracy is easily achieved without it. And he put all the controls readily to hand, making it the minimum ergonomic standard for all combat firearms since.
Most just look to some very short term fielding problems that occurred for a few months back in 1968, all of which were based on compromises degrading the original design, not because of it. Stoner didn't delete chrome plating, didn't specify reusing powder, didn't state the gun never needed cleaning, didn't delay shipping cleaning kits, and didn't insist on putting on the forward assist. PISTON GUN FANBOYS DID, non-engineers who had no clue, who tinkered with the design and got people killed messing with it. Stoner vehemently objected, but by then COLT owned it and was bending over because "the Customer is always right."
And the customer proved to be dangerously ignorant.
Bartholomew Roberts
Moderator
That's funny....at least I don't need these:
http://www.midwayusa.com/product/129...ol-ar-15-steel
http://www.midwayusa.com/product/933...eaning-scraper
http://www.midwayusa.com/product/516...r-and-polisher
I have all DI ARs and I don't need those either; but it does highlight one of the common problems with AR15 maintenance. People spend way too much time trying to make the rifle "white glove" clean, which invariably leads to bad habits.
Some of the ones I recall from the military are things like:
1. Using brake cleaner or laundry detergent to strip a rifle clean of all its lubricant and then not relubricating it before storage (since CLP will invariably pull carbon out of the steel and cause a grey smudge somewhere).
2. Fanatically scraping and polishing AR parts until you've worn most of the protective finish away and removed a few .001" of various critical parts as well. This is especially effective in destroying firearms when you combine it with #1 above.
Your gas tube is black? That's not a big deal. It will function just fine like that. Using abrasives to polish it shiny again is not helpful to function (the gas tube isn't all that thick), even though it may look pretty. Your bolt tail has carbon on it? Again, not a big deal. It is the piston. It is supposed to have carbon on it.
Most just look to some very short term fielding problems that occurred for a few months back in 1968, all of which were based on compromises degrading the original design, not because of it. Stoner didn't delete chrome plating, didn't specify reusing powder, didn't state the gun never needed cleaning, didn't delay shipping cleaning kits, and didn't insist on putting on the forward assist. PISTON GUN FANBOYS DID, non-engineers who had no clue, who tinkered with the design and got people killed messing with it. Stoner vehemently objected, but by then COLT owned it and was bending over because "the Customer is always right."
I agree with most of that statement with this exception; Colt bought the rights to the design in 1959. The Air Force was the first to adopt it in 1962 and the Army didn't start buying it in any quantity till 1965.
Yes, all of the problems mentioned were an attempt by the military to save money and it backfired on them very badly.
I am not one of those who ever claimed that gas piston was better or cleaner than DI, I just decided to give it a try and see how it worked out. If I end up ruining any parts, I will simply replace them. I am also not one who (having used the M16 in the military for a number of years myself) claims that the AR is prone to jamming if it is not spotless. I cannot recall ever having to use the forward assist and have often wondered if it served any real purpose. Yes, you are going to get gasses in the receiver regardless of which type piston system you use, it is just the nature of a semi-auto.
Yes, stripping the BCG to clean it is quicker than removing the hand guards. It takes about 15 seconds to remove and strip the bolt carrier, while removing the hand quards and gas piston takes at least 90 seconds.
The only problem I have is understanding what it is that is supposed to cause carrier tilt. I have yet to see a decent explanation of this. Like I said earlier, you either have a steel rod pushing the bolt carrier back or you have hot gas doing the same thing. Why would one cause any more tilt than the other?
Sinlessorrow
New member
Slappy go look at any pistin gun they all have skids.
The issue with older ar pistons was that he op rod hits the carrier key and pushes it back, this force would tilt the carrier up in the front and down in the back, this was fixed by enlargine the tail of the carrier and giving it skids.
The DI system sends gas into the carrier at the bolt tail which pushes the bolt forward, takig pressure off the lugs, at the same time the pressure send the carrier straight back unlocking the bolt, because the piston in DI is located center inside the BC it sends the BCG straight back centered
The issue with older ar pistons was that he op rod hits the carrier key and pushes it back, this force would tilt the carrier up in the front and down in the back, this was fixed by enlargine the tail of the carrier and giving it skids.
The DI system sends gas into the carrier at the bolt tail which pushes the bolt forward, takig pressure off the lugs, at the same time the pressure send the carrier straight back unlocking the bolt, because the piston in DI is located center inside the BC it sends the BCG straight back centered
The op rod in the Osprey system fits into what would be the gas key on a DI gun. It fits into the "gas key" after fitting thru a steel bushing in the front of the receiver and the other end of the rod is conected to the piston, which fits into the cylinder that is pinned directly to the gas block in the same manner the gas tube used to be. There are no springs, the buffer spring takes care of any need for a spring. The fact that the rod fits about an inch into the "gas key" and the bushing in the receiver is just large enough so that the rod cannot move any direction except fore and aft, and the piston/cylinder is curved (almost a semi circle) to fit the contour of the barrel make it hard for me to see where there is any room for tilt. Again, I have never felt that the conversion was solving a problem with hot gasses or carbon build up, but contrary to what some have said here, it seems to reduce any felt recoil because any excess gas is vented under the handguard instead of being directed at the bolt. The system is self regulating so there is no need for adjustments when the weapon is suppressed and it also vents heat out under the handguard, which would likely only be a factor when shooting in full auto mode. I just compared the two Bolt carriers and the one from Osprey defense is not only a little larger in diameter (.007") but it also uses the heavier M16 style bolt carrier as opposed to the AR15 style that came with the weapon.
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Bartholomew Roberts
Moderator
slappy said:Like I said earlier, you either have a steel rod pushing the bolt carrier back or you have hot gas doing the same thing. Why would one cause any more tilt than the other?
As Sinlesssorrow noted, the push on the AR15 bolt carrier is straight back from the bore. So it travels straight back. With an AR15 piston conversion, the push is from the gas key. On rifles designed from the ground up as piston rifles, this is usually not an issue since all of these rifles have rails built into the upper receiver on which the bolt carrier rides. An AR15 gas piston is using the original AR15 receiver, which doesn't need rails and doesn't have them, so the bolt carrier has room to move around in the receiver when off-axis force is applied.
A secondary issue is that the gas key isn't designed to handle that level of force originally and gas piston conversions that don't account for this in their design can have the gas key/gas key screws shear off.
one from Osprey defense is not only a little larger in diameter (.007")
Exactly. One way many piston manufacturers deal with the issue of tilt is to add skis on the back of the carrier, connect the carrier to the buffer, or make a fatter back end on the carrier to reduce the amount the carrier can move. All of these work to some degree, though they do so at the expense of reducing the amount of internal clearance between the BCG and receiver in a design that some already criticize as being too tight.
OK, I think I am starting to get your point. You are saying that the gas entering the gas key blows the bolt forward causing the carrier to be forced rearward and since it is the force of the bolt moving forward that moves the carrier rearward, it is a straight line motion. Am I on the right track here, finally?
Technosavant
New member
OK, I think I am starting to get your point. You are saying that the gas entering the gas key blows the bolt forward causing the carrier to be forced rearward and since it is the force of the bolt moving forward that moves the carrier rearward, it is a straight line motion. Am I on the right track here, finally?
Yes, you're on the right track. Folks can split hairs over the actual events inside the bolt carrier (I've seen it done), but generally you're correct. The gas being redirected into the bolt carrier by the gas key is how the recoil impulse is put into a straight line with the bolt, making it easier to handle. This is also why carriers that are chromed on the inside are easier to clean- that's where carbon tends to collect.
Sinlessorrow
New member
Heres a ut away that explains how it all works in a DI system
http://www.ar15.com/content/page.html?id=535
http://www.ar15.com/content/page.html?id=535