Idea for a gas operation

[45_auto]

When firing, the bolt is in a fully locked position, the fully locked bolt moves backwards 1mm allowing the gas pressure to flood the chamber past the locking lugs.

Hot gas flowing past precision machined rotating locking surfaces is not a good thing. And as others have pointed out, trying to keep the brass in one piece with the bolt head moving while under full pressure is not going to be trivial.

Your design is basically an AR15 with the gas flowing past the case and bolt head instead of down a gas tube to force the bolt carrier rearward.

It's much more practical (cheaper to manufacture, less wear on critical surfaces) to keep the hot gas away from your precision machined locking surfaces by porting the gas directly into the bolt carrier (AR15), or by using a piston attached to the bolt carrier (AK47, Garand, M14, etc).

What advantages do you perceive that your design has over a typical Ak47 or AR15 gas system?

[Dixie Gunsmithing]

45_auto,

According to the barrel length, the port if placed down the barrel a good bit to help with the locking delay. On the AR-15, it is all the way down at the front sight, and is similar on the AK.

On the AR or M-16, that was the major design flaw, in the gas tube design. If he had used a piston and rod like on the AK, it would have been a much better design. Of course, they are making these conversions now, which I think makes the better gun. Another plus is, it keeps the gas out of the receiver, and the piston rod does the job of separating the bolt instead of gas. Now, if they would modify it, as above, to use a regular bolt cocking handle on the side of the bolt, and take off the ejection cover, it would be a good rifle. One could get rid of the charging handle and the forward assist plunger, too, just by using a regular cocking or bolt handle. Dirt was the reason the forward assist plunger and spring cover was added anyhow, where dirt fouled up the gas system. A good number of our troops lost their lives over that.

[James K]

Hi, DG,

You are going to hear from the AR-15 guys; I suggested on another thread that a piston was better and was nearly crucified by the true believers. Of course Gene Stoner himself later worked on the AR-18 but St. Eugene, like St. John Browning, is not allowed in the canon to deviate from one set of ideas.

FWIW, I consider the AR-18 much better than the AR-15; too bad it came too late for adoption.

Jim

[Dixie Gunsmithing]

Jim, To me the AR-18 was a step ahead, though even on it, there are a few things I'd change. That is just me, thinking like a Gunsmith.

The biggest change between it and the AR-15 is the frame, which is all sheet metal on the 18. That makes it very easy to produce, and similar to the AK. The best part of it, is the piston and rod that works the bolt. They added a cylinder to the rear of the front sight, connected to the gas port. The rod had a spring at the receiver. It was a good simplified version the the AR-15 that got rid of the patches like the dust cover and the forward assist. One could almost call it a US designed AK.

[45_auto]

Originally Posted by Dixie gunsmithing

Dirt was the reason the forward assist plunger and spring cover was added anyhow, where dirt fouled up the gas system.

Interesting info there. How does dirt get into the gas system?

I always understood that the original problems with the m16 were a combination of bad info on required maintenance, the chamber and barrel NOT being chrome-lined, and gas system problems caused by the change from the nitrocellulose-based IMR 4475 powder to the dual-based (nitrocellulose and nitroglycerin) WC 846, which clogged the gas system with excess calcium carbonate.

[Dixie Gunsmithing]

They had it worse than that with the M-16, when it went into military use. Dirt, or really just dust to mud, would foul up the gas tube and bolt carrier. That is why they put the ejector port cover on it. They found that out the hard way, so they patched it with the cover.

The next patch was the forward assist, when a round didn't want to chamber. That could have easily been done with a simple bolt handle, like on any other auto, but on this, dirt would get by it. That's why they made this a sealed unit.

All this and more is why the M-18 design turned out like it did, as they were trying to get rid of the problems they had with this gun. The M'18 ended up with a stamped steel frame, a gas piston/rod for the action, and a regular bolt handle to operate the bolt with, along with no ejector port cover, charging handle, or froward assist. It would take the same magazine as the M-16, if I recall.

[45_auto]

Originally Posted by dixie gunsmithing

They had it worse than that with the M-16, when it went into military use. Dirt, or really just dust to mud, would foul up the gas tube and bolt carrier. That is why they put the ejector port cover on it. They found that out the hard way, so they patched it with the cover.

Totally wrong there. No big deal, lots of bad info on the internet. The military's M-16 has always had an ejection port cover, and Army M-16's have had a forward assist ever since the very first Army buy in 1963 (XM16E1). The original Air Force M-16's (1962) didn't have a forward assist (but they did have dust covers).

The original AR-15 had an ejection port cover. Heck, even the original AR-10 (AR-15 predecessor in .308) had an ejection port cover in 1956!

Originally Posted by dixie gunsmithing

The next patch was the forward assist, when a round didn't want to chamber.

The forward assist was added at the Army's insistence before they would place the first order for the rifle in 1963. The Air Force (using M-16's for several years at the time, since 1962) and Stoner himself argued that it was a bad idea.

The forward assist was on the Army's list of 11 pre-production requirements, and even they later admitted that their testing had not justified the bolt closure device. It was included as a point of pride because the OSD (Office of the Secretary of Defense - Robert McNamara at the time) had vetoed many of their other suggestions.

[Dixie Gunsmithing]

If the rifle was not prone to malfunctioning over dirt, then the Ejection port cover would not be needed. Also, as Bob Dunlap remarks, the forward assist was surely not needed, but a bolt handle should have worked. Of course the military ordered it, but the reason was why? There was no reason to use either assembly, unless it was actually needed. The only reason for the need was dirt.

When you look at the design of Stoner's, he actually used a gas system that was already out, patented about 1943, when working at Armalite. The designer was Erik Eklund for the Ljungman AG-42 of C. J. Ljungman AB, and is mentioned by Bob Dunlap on video AGI-103. The problem with the gas system is twofold.

First, you have a gas tube stuck into the bolt key, and that tube even passes through the charging handle's nose. When the bolt goes back, the gas tube actually comes out of the bolt key, and there, dirt can enter the system. It can go into the tube, or the bolt key via the tube hole, and into the bolt.

The second problem is the bolt having to have a seal, so it acts like a piston and cylinder. Because of this, dirt will clog its function much easier than a two-piece rotary bolt that is driven by a piston actuated action rod, since the fit and tolerances are a lot looser, and no seal is required. Dirt can make its way into the bolt behind the bolt head and cam pin slot, and the action of the bolt opening and closing will drive the debris rearwards and into the cylinder area. They claim that chrome lining it helped the problems, but dirt is dirt.


AR-Cutaway by matneyw, on Flickr


AR-Cutaway-2 by matneyw, on Flickr


AR-Cutaway-3 by matneyw, on Flickr

We're not talking about the AR-15's that we use, as we keep them clean, and in a pretty clean environment. In combat, you have dust, dirt, and mud that can and will get into a gun. Even if they keep them clean, these guns are used in nasty environments. The ejection port cover, and the forward assist, were patches to keep dirt from affecting the design.

AGI-103 AR-15 video:

http://www.americangunsmith.com/app/...5/AR-15-Rifles

Excerpts from video on YouTube:

https://www.youtube.com/watch?v=W68Ey9Sbyto#t=64

[Dixie Gunsmithing]

From a wensource used by Wikipedia on the AR-15:

"Enter the Armalite. In the year of 1957 The US Army requests the Armalite Division of the Fairchild Aircraft Corp to develop a rifle of .22 caliber, lightweight, select-fire, and capable to penetrate the standard steel helmet at 500 meters. The Eugene Stoner, then a designer at the Armalite, began to develop this rifle, based on his earlier design, 7.62mm AR-10 battle rifle. At the same time, experts at the Sierra Bullets and the Remington, in conjunction with Armalite, began do develop a new .22 caliber cartridge, based on the .222 Remington and .222 Remington Magnum hunting cartridges. This development, initially called the .222 Remington Special, was finally released as .223 Remington (metric designation 5.56x45mm). Next year Army tests new rifles, known as Ar-15, and rejects these in favor of the M14. Feeling that the Ar-15 rifle has poor chances to compete with the recently adopted M14 in the US Military, in 1959 the Fairchild Corp, a parent company of the Armalite, sells all rights and manufacturing documentation for this rifle to the Colt's Patent Firearms Manufacturing Company, which had long-time relations with US Military and proven track of selling military guns both in USA and abroad. Colt instantly begins aggresive marketing campaign for the new rifle, stressing its accuracy, low recoil, light weight and modern design. In the 1962, US DoD Advanced Research Projects Agency (ARPA) purchases 1000 AR-15 rifles from Colt and sends those rifles to the South Vietnam, for field trials. Same year brings glowing reports about the effectiveness of the new "black rifle", used by South Vietnamese forces.

"Following the delays in introduction of the ill-fated 'next generation' SPIW system and production troubles with M14, in 1963 Colt receives contracts from US Government for 85 000 rifles for US Army (designated as XM16E1) and for further 19 000 rifles for US Air Forces (designated M16). The US AF M16 was no more than an AR-15 rifle with appropriate markings. The XM16E1 differed from AR-15/M16 by having an additional device, the so called "forward assist", which was used to manually push the bolt group in place in the case of jams. Next year US Air Forces officially adopted new rifle as M16. Same year US Army adopted the XM16E1 as a limited standard rifle, to fill the niche between discontinued 7.62mm M14 rifle and the forthcoming SPIW system (which newer got past the prototype and trial stages).

"With rapidly growing presence of US troops in Vietnam, in 1966 US Government makes the first large purchase of the Ar-15 / M16 rifles, ordering 840 000 rifles for US Armed forces, worth almost $92 millions, and in 1967 US Army officially adopts the XM16E1 rifle as a standard "US Rifle, 5.56mm, M16A1".

"During immediately following years, a number of negative reports apears from Vietnam. M16A1 rifles, issued to US troops in the Vietnam, severely jammed in combat, resulting in numerous casualties. There were some causes for malfunction. First of all, during the introduction of the new rifle and its ammunition into the service, US Army replaced originally specified Dupont IMR powder with standard ball powder, used in 7.62x51mm NATO ammunition. The ball powder produced much more fouling, that quickly jammed the actions of the M16 unless the gun was cleared well and often. It also had different pressure curve, resulting in increased stress on operating parts of the gun. This pitifully combined with the fact that the initial M16 rifles were promoted by the Colt as "low maintenance", so, for the sake of economy, no cleaning supplies were procured for new M16 rifles, and no weapon care training was conducted fro the troops. As a result, soldiers did not knew how to clean their rifles, and had no provisions for cleaning, and things soon turned bad. Another cost-saving measure on the part of the Army was to give up with cromium plation of the barrel bore and bolt group, which made these parts much more sensitive to corrosion and rust that originally designed.

"After several dramatic reports in US press and Congressional investigation of the troubles, several actions were taken to remedy the problems. The 5.56mm ammunition was now loaded using different powders that produce much less residue in the gun action. The barrel, chamber and bolt of the rifles were chrome-lined to improve corrosion resistance. Cleaning kits were procured and issued to troops, and a special training programs were developed and conducted ever since. Earliest cleaning kits could be carried separate from rifle only, but since circa 1970 all M16A1 rifles were manufactured with the containment cavity in the buttstock, that held the cleaning kit. At the same time (circa 1970) the new 30 rounds magazines were introduced into service instead of the original 20 rounds ones, to equal Soviet and Chinese AK-47 assault rifles, which had 30-rounds magazines from the very beginning."

http://world.guns.ru/assault/usa/m16...2-m16a3-e.html

Note that Colt claimed the M-16 was low maintenance, to the point the military didn't buy cleaning kits, or even teach the men how to clean one correctly. Just a powder change and no chrome was not the only problem, since Colt claimed they were low maintenance, and probably dirt proof, as evidenced by the anti-dirt features.

[45_auto]

Originally Posted by dixie gunsmithing

Dirt, or really just dust to mud, would foul up the gas tube and bolt carrier. That is why they put the ejector port cover on it. They found that out the hard way, so they patched it with the cover.

Originally Posted by dixie gunsmithing

since Colt claimed they were low maintenance, and probably dirt proof, as evidenced by the anti-dirt features.

So are you claiming that Colt added the ejection port cover BEFORE or AFTER the military first purchased the M-16??? How exactly did they find out "the hard way"?

Originally Posted by dixie gunsmithing

Also, as Bob Dunlap remarks, the forward assist was surely not needed, but a bolt handle should have worked. Of course the military ordered it, but the reason was why? There was no reason to use either assembly, unless it was actually needed. The only reason for the need was dirt.

Here, I'll type it for you again since you obviously missed it in my previous post:

The forward assist was on the Army's list of 11 pre-production requirements, and even they later admitted that their testing had not justified the bolt closure device. It was included as a point of pride because the OSD (Office of the Secretary of Defense - Robert McNamara at the time) had vetoed many of their other suggestions.

[4V50 Gary]

Dixie Gunsmithing. Those are great cutaway images. Thank you.

[Dixie Gunsmithing]

Gary, those are screenshots I took from around the web, then I made blown up views of sections, which I modified by adding text, etc. It's the best way to show how the dirt can enter into the bolt.

[Dixie Gunsmithing]

45_auto,

They learned the hard way, that their so-called low maintenance gun wasn't low maintenance, and men lost their lives over it. The men took out a gun, believing it could handle dirt, dust, and mud, and found themselves with jammed guns, and lost their lives. Yes, some may be blamed on powder, but according to the men, it was dirt.

The ejection port cover was added, by the manufacturer, because they knew that dirt would affect the operation, thus it was a patch to their original design. They did it before they sold it. The reason why the forward assist was later designed the way it was, was that they knew they had to keep the receiver closed. Colt touted this as low maintenance, when in fact, dirt fouled the gun up, and they knew it. How the military didn't catch this, on those 1000 they bought for field trial, and sent to Nam, which they claim had "glowing reports", is beyond me.

The forward assist was on the 85,000 bought, so one can assume the military knew something was up when they asked for this device, when a much simpler method would have been to remove the cover, slot the receiver, and add a bolt handle to ride in the slot. This was done on the later AR-18. If the AR-15/M-16 worked, why redesign it like the AR-18?

My opinion on the whole ordeal, is that someone in the military wanted the AR-15, since Colt now had it, no matter the flaws, and that is what they got. When men died over it, and it was in the press, the government wanted to blame it on something other than admitting to buying a flawed gun, so they came up with the powder, cleaning, etc, and never once mentioned the dirt the men on the ground did. Never, will the government admit to buying something that puts them in a bad light.

I have a set of four videos on Nam, I believe, made by NBC or ABC News, and there is an interview with some of the men who mention this about their rifles. Mainly, though, it was in the papers at the time.

[Dixie Gunsmithing]

Getting back onto the topic, the Ljungman design might be something to look at.

This design used a gas tube, which went into a cylinder in the front of the receiver, in front of the top of the bolt. The bolt had a piston head attached to the top, and that piston went into the cylinder, when the bolt was closed. When the gun was fired, the gas followed the gas tube back, similar to the AR-15, but instead of going in the bolt key, it fed the cylinder, which drove back a piston that would be in place of a bolt key. The only problem is keeping it clean, but this would, to me, be a much better alternative, and be similar to a short stroke piston. All you need is enough pressure to unlock the bolt, and drive it rearward enough to cycle, stripping a fired case, and allowing a spring to close the bolt. One could use a rotary bolt similar to one on a Winchester 1400.

From World Guns:



One could even modify this, and turn the piston around 180 degrees, and make it spring loaded. The piston would then shove the bolt back from the front of the receiver, and then the piston would retract under spring pressure once the gas pressure dropped. The bolt body would only need a face for the piston to strike against.

[Dixie Gunsmithing]

While I am at it, below are some of the patent images for the AR-18. I didn't include one for the belt fed version.


P1 by matneyw, on Flickr


P4 by matneyw, on Flickr


P2 by matneyw, on Flickr


P3 by matneyw, on Flickr


P5 by matneyw, on Flickr

[45_auto]

Originally Posted by dixie gunsmithing

when a much simpler method would have been to remove the cover, slot the receiver, and add a bolt handle to ride in the slot. . This was done on the later AR-18.

This was actually the first proposal by Colt to the Army's requirement for a bolt closure device. It was rejected because it let too much dirt into the receiver (Black Rifle, pg. 130). Might be one reason the AR18 was never accepted?

[James K]

I am not sure who beat whom on the patents, but MAS in France had a semi-auto gas impingement system rifle working in 1938 (The MAS Mle 38), although production didn't begin until 1940 after it had been slightly modified and renamed the Mle 40. (The Germans upset plans for mass production.)

The ejection port cover was not put on the AR-15 because the Army wanted it; it was on both the AR-10 and AR-15 from day one. I handled AR-10's and AR-15's with the old "upper trigger" and they had port covers.

To me, the main advantage of the AR-18 was the bolt riding on rods, like the M3/M3A1 SMG. While the rifle still used a port cover, the rod system made dirt and garbage in the system pretty much irrelevant as there was plenty of room for it. The takedown system, though, needed the same kind of operating spring capture system as the M3A1, as well as a better folding stock system.

When the forward assist was first put on the M16 (that WAS an Army request), one Ordnance officer told me it was a "jam maker". He wanted a solid bolt handle ("that I can kick with my boot" to eject a bad round), but by that time the AR-15 design was pretty well "set in concrete" and he lost the battle. He felt that if a cartridge was dirty or bent, it should come out, not be forced in.

Jim

[Dixie Gunsmithing]

Jim, they mention the MAS about the patents, but I didn't notice a date.

The AR-18, did have a funny takedown, in that the rods and springs had to be caught, and let out slowly, if I recall. The patent drawings don't show this well.

The rods would make a big difference, along with the bolt having bearing points at the frame, and not full contact. One would need to keep the rods oiled, though. You can tell a lot of thought went into it about dirt.

I always said, that when they saw the ejection port cover, they should have questioned them about why it was there. I never did agree with the outcome on the AR-15 / M-16, but that's just me.

One thing I noticed more, is the full auto trip changing, and the disconnector being moved. The AR-15 was simple in this regard, and I think they might ought to have stuck with that. It seems they wanted to redesign it all. The bolt won't work with the old, though.

[James K]

Another advantage of the AR-18 (not "M18", it was never adopted by the U.S.) was that it could be manufactured in any country that had simple machining and stamping facilities, rather than having to be machined from forgings on high precision equipment. That meant it was not only cheaper to make in the U.S., but allied countries could buy a license and make their own rather than having the U.S. provide them, a considerable savings in foreign military aid.

The problem was that both the M14 and the M16 were driven by politics rather than a matter of selecting the best rifle. When U.S. Marines stormed ashore in Lebanon in 1958, they were met, not by gunfire, but by women in bikinis. The U.S. was further the butt of jokes because the troops carried WWII M1 rifles, when just about everybody in the Middle East had an AK-47. So it became a matter of national pride to field the M14 and move on to a better selective fire weapon as soon as possible.

That drove the need for a light automatic rifle, and the AR-10 was the only game in town. Meanwhile, the Army was playing with small caliber ammo, and thought a scaled down AR-10 would be the best of both worlds.

There is a lot more to the story. For those interested, I recommend "The Black Rifle" by Blake Stevens and Ed Ezell.

Jim

[Cutaway]

The image posted is just a rough idea of the operation. Im not saying it has advantages over the existing gas/delayed blowback operations but thought it could be simplified and compacted. I would imagine gas/residue to foul up the receiver but this could be sorted out if the cam groove was redesigned to delay the opening as well as the piston head slightly angled/channeled to divert the gas out the ejection port. Also when firing, the locking lugs could shut off the gas to the piston head with the remaining gas in the barrel to operate the reloading of the weapon. For extra reliability, it would depend on the ammo cartridges used.

[Gunplummer]

Now I am curious. Someone stated that the Army M-16's always had the forward assist. We redid hundreds (Maybe thousands) of uppers over to the A-1 model. Most as I remember were H&R's, there may have been some General Motors lowers, I don't remember for sure. I do remember the H&R's because of the lousy fit between the upper and lower receiver.

[45_auto]

The Army never had an M16. First buy for the Army was DA-11-199-AMC-508 in Nov 1963, $13,500,000 for 104,000 rifles:

85,000 with bolt assist designated XM16E1 for the Army and Marines, and 19,000 called the M16 with no bolt assist for the Air Force.

XM16E1's were first issued in Apr 1964.

In Oct 1964, the original order was increased by 33,500 M16's for the Air Force, 240 M16's for the Navy, and 82 M16's for the Coast Guard.

In Jul 1965 the Air Force ordered an additional 36,682 M16's.

Second buy for the Army was DAAF03-66-C-0018 in Jun 1966, which increased the original XM16E1 order to 201,045 rifles.

The XM16E1 was officially classified as "US Rifle, 5.56mm, M16A1" in Feb 1967.

The only M16's were the early Air Force, Navy, and Coast Guard guns with no bolt assist.

Were you working on Air Force guns?

[James K]

Very interesting, but let's get back to the OP's idea. Here is why it won't work.

Gas at the case mouth is under high pressure. Given an exit, it moves very fast. If it can get past the case mouth into the grooves you visualize in the chamber and strike the bolt carrier, the latter part will move backward at very high speed and unlock the bolt before chamber pressure drops to safe levels.

The result will be an unsupported case at an internal pressure close to maximum chamber pressure. The bolt carrier and bolt will be blown back at high speed and damage themselves and the receiver. Further, the case will let go, the hot gas will escape and continue to expand, blowing the receiver apart.

There is a reason why designers of automatic rifles must make sure the pressure drops before the bolt opens.

Of course, you won't take my word for it, pointing out, correctly, that I have not tried your idea. My response is that you can try it yourself at small cost. A couple of thousand dollars should get you a mockup. But don't make the common mistake of thinking that because something works in a nice drawing, it will work in the real world. Drawings don't operate at 50,000 psi!

Jim

[Dixie Gunsmithing]

There has to be an unlocking delay for any action of a large caliber to work, without rupture of the cartridge. This has been done by several means in the past, but it mainly is done by venting the gas over half way down the barrel, so that by the time the gas acts upon the action, the bullet has cleared the muzzle, and the gas pressure drops. Generally, this delayed action is a combination of the gas acting on a piston, and the weight of the action components, including the bolt, and the recoil spring. An impulse is all that is needed to actuate the action, so by the time the gas reaches the piston, it is already about to start dropping off.

The above is why I mentioned the Benelli inertia operated bolt. With it, venting gas isn't needed, but one could use a combination, I would guess. However, you have gas acting on the bolt, via a piston, which is the cartridge itself, so there is no need to divert any gas around it. How this would work with rifle cartridges, I have no idea.

[James K]

Note, though, that the Benelli doesn't open until the recoil force has dissipated, which means the bullet or shot charge is long gone from the barrel. The Benelli design is clever and innovative, but it doesn't reinvent the laws of physics.

Jim