View Full Version : Why no new DI designs?
Let's get this out of the way immediately: I really don't want to start another "piston vs. DI thread here". I am genuinely curious about what I'm going to ask.
Why do no new designs use direct impingement gas systems? The AR15 is obviously successful and has "proven" that the system works so how come newer (i.e.: FN SCAR, Tavor, BREN 805/806, AK12, etc) designs are all piston-operated? If the simple answer is that "pistons are better" then why are piston-operated AR15s not more popular (indeed, why are they so widely panned)?
It just seems odd to me that the AR15 should be so successful without having its gas system being copied even once. :confused:
Knight's has basically been the only one to "tweak" the DI system, save for LMT and the Enhanced BCG (which I have two of and love 'em BTW).
There was the LR-300 and the Armstech gas trap/DI.
Neither seemed very successful.
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There was the LR-300 and the Armstech gas trap/DI.
Neither seemed very successful.
Forgot about those.
There was the LR-300 and the Armstech gas trap/DI.
Neither seemed very successful.
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I wasn't aware of either of those. They both look rather AR-esque; it doesn't seem like a huge leap for them to be DI.
I guess what I'm wondering is why there isn't a DI version (or at least conversion) of the SCAR or similar? Wouldn't that work just as well and be lighter and cheaper than a piston?
Mr. Goodtimes
12-06-16, 19:22
Because of the bullshittery that's plagued the AR-15 for 60 years... that DI is inferior to piston and unreliable.
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SomeOtherGuy
12-06-16, 19:38
Two reasons:
1) The original AR-15 design is a nearly perfect expression of the concepts: not only the DI producing a soft action impulse, but also the recoil in-line with the shoulder stock and the use of newer, high strength-to-weight materials to produce a rifle that, at least in its original form, was much lighter than competitors while still being adequately strong and durable.
2) However, the DI system does have some drawbacks for common military use. Every design choice has pros and cons. DI makes it easier to make an accurate rifle and have a really smooth recoil impulse, which is why you see it in modern designs for precision (KAC SR-25, LMT MWS) and 3-gun gaming use (various). The cleaning disadvantages, although modest, are very well known.
Basically I think that the minor disadvantages of DI, coupled with the nearly perfect execution of the concepts in the AR-15 design, means that a firearm designer can't really improve on the AR-15 with a DI system, but they can use a conventional piston system and claim to have an all-new "superior" design, with any issues of weight, accuracy or complexity being answered with purported reliability and durability benefits. I'm aware of the military M4 testing and won't bother stating an opinion on whether a well executed DI system is inferior to a well executed conventional piston system.
One thing I do notice is that most forces that operate in arctic conditions do not use DI systems. The US and Canada do, of course, but the Scandinavian countries use other designs (Norway - HK416 with piston; Sweden - HK G3 and apparently moving to LWRCi piston-AR; Finland - AK-derived Valmet; Russia - AKM; China and North Korea - AKM and other piston designs; etc.). I suspect that the DI system is more sensitive to outside temperatures than piston-in-block designs, because the operating gas has to go through 6, 8 or 12 inches of highly exposed, heat conductive tubing before it gets to the operating piston.
AS-50 is DI.
https://www.youtube.com/watch?v=XCSaWJDZ7oQ
Because business is to make money and you have to sell people on something. The biggest complaint about the ar is reliability, and it's a joke. Shitty companies make unreliable ars, then the same companies come out with piston guns and retro fits to fix their problems, meanwhile colt and bcm shooters just shoot.
If you make a new di rifle, you can't claim better action, and how are you going to compete with the egos and market share?
Because small arms design has pretty much stagnated. Most "new" designs are highly derivative and thus end up being evolutionary rather than revolutionary. Let's face it-nowadays a JM Browning could never afford to compete for a military contract, matter how great his designs.
Because business is to make money and you have to sell people on something. The biggest complaint about the ar is reliability, and it's a joke. Shitty companies make unreliable ars, then the same companies come out with piston guns and retro fits to fix their problems, meanwhile colt and bcm shooters just shoot.
If you make a new di rifle, you can't claim better action, and how are you going to compete with the egos and market share?
Exactly. We're talking about an industry that is still too retarded to get gas ports the right size. There's no need to improve on DI. It works wonderfully when you quit catering to ARFtards who want to bumpfire garbage ammo into the side of a hill.
Exactly. We're talking about an industry that is still too retarded to get gas ports the right size. There's no need to improve on DI. It works wonderfully when you quit catering to ARFtards who want to bumpfire garbage ammo into the side of a hill.
Have a little faith. For the price of a good press, they can upgrade to bumpfiring match ammo into a hillside! ;)
Seriously though, there's probably just not much left to gain in a new DI design. And as far as pistons go, I don't know that any of them are really that much better than any other of them. I'm not saying there aren't different quality levels or application preferences, just that they all seem proprietary against each other without a clear winner.
Because business is to make money and you have to sell people on something. The biggest complaint about the ar is reliability, and it's a joke. Shitty companies make unreliable ars, then the same companies come out with piston guns and retro fits to fix their problems, meanwhile colt and bcm shooters just shoot.
If you make a new di rifle, you can't claim better action, and how are you going to compete with the egos and market share?
Well, there is more to it than that.
The idea is to make money, that is true. In order to make a new design, DI or otherwise, you need to spend some money developing it so it works.
Why bother, if you can find on the internet the drawings to almost every important part of an M16, and there is no need to spend money seeing if your "new and better" design is really all that new and better.
While I am a bit of a piston fan, I will freely admit that their existence (and relative success) is due more to being "new and different" rather than "better". "New and different" always sells, even if it isn't really all that much "better". And, development of a piston AR is a lot cheaper than development of a completely different rifle design, think of all the things that you don't have to worry about . . .
The main benefit of "DI" on the AR15 is that everything is in-line. What other way could you design a rifle with everything in-line and not have it be an improved version of AR15? What benefit would there be to a DI rifle if wasn't an in-line system?
The main benefit of "DI" on the AR15 is that everything is in-line. What other way could you design a rifle with everything in-line and not have it be an improved version of AR15? What benefit would there be to a DI rifle if wasn't an in-line system?
Ever see a VZ-52 operating system, all the operating parts are co-axial with the bore, although the rifle is of conventional layout. Give it a pistol grip and a straight stock...
Then there is the SIG 510 (aka STG 57), that's all "in-line".
The FG-42 is not fully "in-line", but the barrel bore is in-line with the shoulder and the piston thrust line is below that, so there is little muzzle rise. (Less that an AR-10, with a full power round.)
A few other with "everything in-line" but not a version of the AR:
MG-42
MG-34
MG-30
MG-15 (ground mount)
MG-81 (ground mount)
MKb-42
Johnson LMG (second model)
AA-52
Dror
Lathi L-39
Barrett's .50 caliber semi-automatic rifles
FAMAS
Sterling's experimental 7.62mm rifle could be (the actual prototype was not fitted with a stock)
Gerät 06H
T31
And, that's just off the top of my head, I am sure there are a few more.
Stuff that is very close to being fully in-line:
Ljungman (could be in the other list if they were not conventionally stocked)
Hakim (could be in the other list if they were not conventionally stocked)
Rasheed (could be in the other list if they were not conventionally stocked)
FN Bullpup
EM-1
EM-2
TRW's Low Maintenance Rifle
XM248 (the bore was in line with the should and there were two pistons one above, and one below to cancel out the piston off-axis thrust...)
Ever see a VZ-52 operating system, the operating parts are co-axial with the bore, although the rifle is of conventional layout. Give it a pistol grip and a straight stock...
Then there is the SIG 510 (aka STG 57), that's all "in-line".
The FG-42 is not fully "in-line", but the barrel bore is in-line with the shoulder and the piston thrust line is below that, so there is little muzzle rise. (Less that an AR-10, with a full power round.)
A few other with "everything in-line" but not a version of the AR:
MG-42
MG-34
MG-30
MG-15 (ground mount)
MG-81 (ground mount)
MKb-42
Johnson LMG (second model)
AA-52
Dror
Lathi L-39
Barrett's .50 caliber semi-automatic rifles
FAMAS
Sterling's experimental 7.62mm rifle could be (the actual prototype was not fitted with a stock)
Gerät 06H
T31
And, that's just off the top of my head, I am sure there are a few more.
Stuff that is very close to being fully in-line:
Ljungman (could be in the other list if they were not conventionally stocked)
Hakim (could be in the other list if they were not conventionally stocked)
Rasheed (could be in the other list if they were not conventionally stocked)
FN Bullpup
EM-1
EM-2
TRW's Low Maintenance Rifle
Without me Googling every single one, which ones don't have an offset piston or recoil operation?
Without me Googling every single one, which ones don't have an offset piston or recoil operation?
In the first list, none of them have an "off-set piston", the VZ-52 and STG-57 don't either, only the FG-42, EM-1, EM-2 and the LMR have offset pistons (these are all listed as "close-to-but-not-quite").
What's the beef with recoil operation? It's a great way to keep everything "in-line", and there are generally fewer parts than gas operation. That's why the Germans used in rather extensively for their MGs...
(Oh, and of the first three, plus the following list of 15, eight (8) are not recoil operated.)
The Ljungman/Hakim, Rasheed, T31, MKb-42, and VZ-52 are gas operated, and all the moving parts are fully "in-line", having a axis of motion coaxial with the bore...
In the first list, none of them have an "off-set piston", the VZ-52 and STG-57 don't either, only the FG-42, EM-1, EM-2 and the LMR have offset pistons (these are all listed as "close-to-but-not-quite").
What's the beef with recoil operation? It's a great way to keep everything "in-line", and there are generally fewer parts than gas operation. That's why the Germans used in rather extensively for their MGs...
(Oh, and of the first three, plus the following list of 15, eight (8) are not recoil operated.)
The Ljungman/Hakim, Rasheed, T31, MKb-42, and VZ-52 are gas operated, and all the moving parts are fully "in-line", having a axis of motion coaxial with the bore...
You have to admit that the AR15 does the in-line design about as well as possible. It is literally a tube with the only thing offset being the gas tube and gas key.
What benefit would there be to a DI rifle if wasn't an in-line system?
This is the point I was trying to get to. A DI rifle that is also in-line would basically be an upgraded AR15, right?
I literally just read this on ARFCOM. Why am I always seeing double threads in two different forums?
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So the short answer is "they don't put the DI system in new rifle designs because people wouldn't buy them due to hyperbole that they read in gun magazines from 1966-2003?"
I thought that it would be more complicated than that...
There's many possible gains when not limiting ourselves to the confines of our current base receiver. There are some issues with that though at this time. The cost is high without a huge gain, plus the base receiver grows in size.
How many of us would pay the price for a 5.56 DI gun sized up similar to SR-25 dimensions to contain many of the "improvements" with a cost that is similar to a SR-25 range? Most would not, it is simple "supply and demand". The market does not demand that at this time, and there are too many copycats for base systems to compete with.
Many of our "gripes" as mentioned in another thread on this site have been already addressed. Griping about issues and demanding solutions in volume is what it's going to take to do this while a manufacturer does this in a way that keeps his doors open and not going out of business.
The Ljungman/Hakim, Rasheed, T31, MKb-42, and VZ-52 are gas operated, and all the moving parts are fully "in-line", having a axis of motion coaxial with the bore...
As the Ljungman family of weapons are direct impingement, the force of the gas acting on the carrier is not in direct line with the bore. However, the off center thrust is likely to have a negligible affect on muzzle rise.
Instead of using a direct impingement system, the AR uses a piston & expansion chamber (fancy term for "cylinder") inside the carrier. The thrust from the gas is in direct line with the bore. With a direct impingement system, the gas acts directly against the exterior of the carrier.
My guess as to the reason no other rifle uses the AR gas system is, that by the time the basics of the design that are needed for it to work are adopted, you've got an AR
First off, the AR15 is not "DI". Never was, and probably never will be.
The AR15 has a piston located in the carrier group, and is formed by the bolts tail, and the carrier.
Secondly, the AR15 has seen constant development for over 60 years, on top of being an already great design.
As the saying goes, "why mess with success"
Serious Account
12-08-16, 19:20
Daewoo K1 is DI
Q is tagging the new Honey Badger with #notanar but it looks to be DI. Has a thread on barrel instead of traditional barrel nut and Knights mod 2 style thread on gas block nut and some kind of proprietary buffer and PDW stock system.
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Check this out! https://www.instagram.com/p/BOVfTd-jpVt/
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Microadventure
12-23-16, 09:54
the problem with piston ARs is that they are a hack mod to the most remarkably modular existing design ever seen. the only thing out there that matches the AR for modular interchangeable and flexible design is the PC most of us are using to write and view this.
the problem with piston ARs is you abandon the ability to buy replacement parts in Butte, Montana an hour before the gun store closes. you trade parts interchangeability for a kludged design where the only parts source is the company that hacked a functional design, if they are still in business. not a wise tradeoff. like taking a long road trip in a Corvair, leaving an F150 in the driveway..
The Dumb Gun Collector
12-23-16, 11:39
I am going to use Piston vs DI as my terms. I know the difference, and am going to stick to the usual language.
Piston systems are probably easier to design and perfect. The DI system works fantastic within certain parameters but seems to take some hard thinking when you change things up. Look how long it took them to perfect the shorty guns...Colt started tinkering with them in the late 60s and we didn't get where the commando length guns were totally gtg until the early 00s. There are more buffer weights, designs, etc than types of ammo available. You can go insane wading through the gas port esoterica on this site. Most piston guns tend to be clean sheet and made with one or two variations in mind--so they tend to work. The AR has had to evolve quite a bit since the 1950s. This gun has evolved from a 20 inch rifle expected to run exactly one type of ammo (and good Lord they ran into trouble when they tinkered with the powder) to guns down to 10 inches that are expected to run bullets from 55-80 grains without choking. The AR is an engineering marvel and is without a doubt the most mature system available...but my guess is that piston systems just make more sense from a clean sheet engineering perspective.
That being said, I prefer the AR because it is basically perfect for me ( I am a short right handed male). I have shot an average of 4000 rounds per year through my colts and have had exactly one problem---a case of out of spec wolf ammo about 5 years ago. I have had far more reliability and durability issues out of my AKs than my Colts.
I actually owned a 416 upper a fee years back when I also owned an M16A1. I ran it as Gott intended, full auto suppressed. It was excellent and totally reliable. But now that I am out of the full auto AR game I see no need for super heavy short piston guns.
Check this out! https://www.instagram.com/p/BOVfTd-jpVt/
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Links to a bolt action receiver?
KB at Q does have many interesting items posted on Instagram. Sure bet to drain my wallet for a few things.
Links to a bolt action receiver?
KB at Q does have many interesting items posted on Instagram. Sure bet to drain my wallet for a few things.
My bad, wrong link. Somebody needs to take away my phone. Check out the component interfaces on the new Honey Badger though. https://www.instagram.com/p/BNrrBftDyfp/
You have to admit that the AR15 does the in-line design about as well as possible. It is literally a tube with the only thing offset being the gas tube and gas key.
This is the point I was trying to get to. A DI rifle that is also in-line would basically be an upgraded AR15, right?
HK G3/91 totally in line op system. The A3 retractable stock is pretty much in line, at least to the same extent the M16 is. Both have bore axis about 1" below the top of the stock.
My bad, wrong link. Somebody needs to take away my phone. Check out the component interfaces on the new Honey Badger though. https://www.instagram.com/p/BNrrBftDyfp/
The threaded gas block retention like the 1990's SR-25s is good to see, I like that KAC and others have been going back to that.
The changes in the receivers to accommodate their retractable stock is also interesting.
HK G3/91 totally in line op system. The A3 retractable stock is pretty much in line, at least to the same extent the M16 is. Both have bore axis about 1" below the top of the stock.
The recoil spring and charging handle rod are offset from the center line though.
sevenhelmet
12-27-16, 09:28
the problem with piston ARs is that they are a hack mod to the most remarkably modular existing design ever seen. the only thing out there that matches the AR for modular interchangeable and flexible design is the PC most of us are using to write and view this.
the problem with piston ARs is you abandon the ability to buy replacement parts in Butte, Montana an hour before the gun store closes. you trade parts interchangeability for a kludged design where the only parts source is the company that hacked a functional design, if they are still in business. not a wise tradeoff. like taking a long road trip in a Corvair, leaving an F150 in the driveway..
THIS. It's the main reason I prefer "DI" AR-15s.
The recoil spring and charging handle rod are offset from the center line though.
1- charge handle does not reciprocate
2- recoil spring is maybe 3/4 - 1" above the bore. We'd be getting pretty nuanced in forces, I'd be surprised if it was measurable without instrumentation. And none of it is above the barrel, it's all centered over the receiver. So should not result in barrel whip
So I'll play the rotating force of the AR bolt unlocking and the cam pin vs the non rotational HK roller bolt.
1- charge handle does not reciprocate
2- recoil spring is maybe 3/4 - 1" above the bore. We'd be getting pretty nuanced in forces, I'd be surprised if it was measurable without instrumentation. And none of it is above the barrel, it's all centered over the receiver. So should not result in barrel whip
So I'll play the rotating force of the AR bolt unlocking and the cam pin vs the non rotational HK roller bolt.
The force from the cartridge will push the bolt straight back, but the recoil spring is above the bolt and will make the entire bolt assembly cam downward. On an AR15 the recoil spring is directly in line with the cartridge. The only forces on the bolt carrier group that aren't in line are the magazine spring force and hammer force which most other designs have as well. I don't believe the cam pin would have much effect since it would be torquing the bolt carrier along the axis and since it and the upper receiver are round, there wouldn't be any harm from it. If the recoil spring was directly behind the bolt assembly on an HK and the stock a little higher it would be a completely in line design as well.
The in line design is a pro of the AR15, right? Why make a "DI" rifle that is not in line? What benefit would there be to that?
Before we drift off into left field too much, can we discuss what actually happens during operation of some different DI AR variants and compare and contrast those to see what we have, what we want, and what we do not want to have?
Does chamber pressure push the bolt straight back? I would say no (it doesn't), the deflection can depend on the active lugs effected by the stresses and strains by the chamber pressure and BE. Knowing that, should that deflection be restrained by external forces? i.e. reduced space for that deflection by the carrier and/or upper? (again, no). We know that the pressure event during firing takes a time duration, are there other options that can help or hurt this when added to other events? (yes there are many).
There are some timing events in the action sequence that can help reduce stresses and strains of just the bolt during its own rapid pressure and de-pressure event.
This is not the only event that we can look into. There are many in this system, but maybe we can start a conversion starting with the bolt during firing and going outward from there. Might help out some people looking at in a different way with sequence instead of other ways to see results.
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