M16 myths

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lysanderxiii

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It order to not clog up another thread, and be admonished again, I'll start my own.

Ball powder was the problem - myth
This is contrary to everything I have read and heard. Can you provide evidence proving it is a myth?
1) Ball Powder

Ball powder was a necessity brought about by the case volume and the energy density of available IMR propellants. In order to meet the velocity and pressure requirements, a certain energy density was required of the propellant. IMR 4475 lots with acceptable energy density had to be cherry picked for use in military ".222 Special" loads. This was fine for small lots required for test and evaluation, but such cherry picking was impractical for orders of upwards of half a billion rounds. This fact was plainly evident by the fact that no approved ammunition manufacturer would submit a bid on FY 64's 5.56mm ammunition requirement.

But, ball powder increased the cyclic rate. Yes, it did. This would have been hashed out had testing been done on the rifle-ammunition system, which is what both Colt and the Army suggested, however the OSD nixed additional testing.

Ultimately the newer heavier buffer design solved the cyclic rate problem. A new buffer was required for other reasons anyway. One, it did not absorb energy as design when dirty or corroded. Two, it caused bolt bounce and failure to fire in full automatic.

(As an aside, IMR 4475 was also used in 7.62mm ammunition, it was found to have excessive pressure variation, and poor temperature stability. In short, it was pretty much a failure as a propellant, that's why you don't see it on the store shelf.)

But, it was dirty and caused cases to stick. No, failures to extract were mainly the result of improper case hardness. If the case is too soft it will not retract after swelling due to the pressure, this can result in stiff extraction to a case stuck hard in the chamber. The first drafts of the 5.56mm ammunition specifications did not specify a case hardness gradient, nor a minimum head hardness requirement, and these values were left to "best commercial practices". .222 Remington, which is what .223 is based on was a bolt action case (name a semi-automatic chambered for .222 Remington in 1959-60), bolt actions are more forgiving in this regard.

But, it was dirty and clogged up the gas tubes. Yes, and no. This was only an issue with one or two lots. And, it took some time to accumulate to the point where it became a problem, 5,000 to 6,000 rounds. Further, Winchester, had studied this issue very early in the M16 development and recommended lot of WC846 made for 5.56mm loading have lower CaCO3 content. This low CaCO3 WC 846 would be spun off as WC 844 a few years later.

In short, WC 846 was the only viable propellant option, and that's why ball powder is still the primary propellant to this day, WC 844 in M193 and M855, an SMP 842 in M855A1. And, for all the stick powder fans out there, yes, the search for an acceptable alternate stick propellant for 5.56mm, IMR 8208 and CMR 170 were developed and accepted, but were never as popular with manufacturers.

Much of this information is in "The Black Rifle, M16 Retrospective", Stevens, B. R. and Ezell, E. C. Additional information comes from: "Bulk Density of Extruded Propellants for Small Caliber Ammunition," "Investigation of Gas Tube Fouling Characteristics of M193 Ball Cartridges in the M16A1 Rifle," "Investigation of Ballistic and Chemical Stability of 7.62mm Ammunition Loaded with WC 846 and IMR 4475 Propellant," "Special Test of 5.56mm Ammunition," "Product Improvement Test of Redesigned Buffer for the M16A1 Rifle."
 
Tumbling bullets - myth
Not in flight, but M-193 bullets usually break apart, or flatten, when hitting flesh, Then they go all over the place in the body.
The ARPA report of the initial field testing of the AR-15 in combat alludes to the "buzzsaw" bullet.

Bouncing off twigs - myth
Of course they don't "Bounce off of twigs" but they can be deflected from their flight path.
"Effects of Tropical Grass on Projectile Performance" and "Yaw Induced in Bullet Flight by Passage Through Foliage"

Both of these reports come to the conclusion that the 5.56mm and 7.62mm bullets are effected by passage through brush to the same extent.

Stoner made it right, the Army screwed it up - myth
Stoner was a pioneer in using unconventional materials in weapons construction. Whether or not he "Got it right" isn't for me to say, but Stoner left Armalite in a huff when the Army added that forward assist to the gun. He was dead set against it. At least that's what the books in the Arsenal Museum's archive section say. The Arsenal Museum has one of the original prototypes of the F/A on display. It is a crude, cobbled together contraption. Note the green stocks on the very early guns. These guns have the early 1-14 twist barrels.
Stoner and Armalite had nothing to do with, and nothing to say about, the forward assist. Armalite sold the AR-15 design (and all patent rights, to include those used on the AR-10) to Colt's Manufacturing, Inc in September 1959. The forward assist started development in 1963. Colt's did not reach back to Armalite for permission for anything.

As to "getting it right" F.E Sturtevant, one of Colt's engineers, has as many patents in the M16/AR-15 as Stoner.

Colt had to make 165 changes to the design, and a tolerance study found a few hundred potential interference areas in the drawings.
 
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The switch to ball powder also necessitated the first upgrade of the extractor spring. The extractor spring was again upgraded in the M4.

Good stuff, lysander
 
Both of these reports come to the conclusion that the 5.56mm and 7.62mm bullets are effected by passage through brush to the same extent.

I've often wondered about that... in any bullet. You often hear the phrase 'brush bustin' ' about lever-action cartridges... and, yet, a FN bullet would likely deflect MORE going through brush than say a spire point (FMJ.)

Wasn't the instability of the 55grn bullet linked to the lazy (1:14?) rifling? I'm going off memory, here...
 
If I had a dime for every time I've seen someone blame the early M16 problems on the switch to ball power. Usually this comes from people with no understanding of handloading or how it affects function in an AR15/M16. In fact there is nothing wrong with ball powders in general, or the ball powder they switched to specifically. The problem was that the load they used had gas port pressures that were outside of what the rifle was designed to operate at. It was just a poorly vetted mismatch of hardware and powder burn rate. If the rifle had been designed with an appropriate gas port diameter for that powder in the first place, or had they chosen a ball powder with a slightly different burn rate to match the gas port pressure that the rifle was designed for, then they never would have had the over gassing problem.
 
I've often wondered about that... in any bullet. You often hear the phrase 'brush bustin' ' about lever-action cartridges... and, yet, a FN bullet would likely deflect MORE going through brush than say a spire point (FMJ.)

Wasn't the instability of the 55grn bullet linked to the lazy (1:14?) rifling? I'm going off memory, here...
What the reports found was, yes, bullets that hit foliage have a yaw induced upon them due to impact. If the bullet has enough stability to recover from the yaw it will continue, albeit in slightly different direction. If the induced yaw is excessive, it will tumble and rapidly become harmless.

In the linked test, a row of 1 inch dowels is spaced so the bullet has to hit one of them. Then you shoot through them and see what happens. This is biased in favor of the heavier bullet as the because, 1) the bullet has to hit a dowel, and 2) the dowel size is constant (and fairly large).

The Army's test was a little bit simpler, it was just a random section of southeastern undergrowth and they shot through it.

Z5PJCyY.png

The size of the twigs, branches and leaves in real life varies, and two, and the spacing of the branches, twigs and leaves in undergrowth varies. And, while the size of a branch that will deflect or tumble a .22 caliber bullet is smaller, the smaller diameter of the .22 makes the probability of hitting such a branch less likely. The probability of a being lethal after passing through underbrush is about the same, and the probability of hitting the projected point of impact ("E" in the drawing) is about the same.
 
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Another widespread M16 myth is everybody was either negligently stupid, or negligently frugal to chromium plate the bore and chamber of the M16.

False.

Before the Army first bought its first handful of AR-15 from Armalite back in 1958, they knew that chromium plating the bores and chambers would be a good idea. However, modern ubiquity leads people to believe that chromium plating a bore is easy and anyone can do it. In June of 1957, Springfield Armory published a report on the challenges of plating .22 caliber bores with (then) current technology. The problem isn't just getting chromium to stick to the bore*, but etching off a uniform thickness and then plating back on the same uniform thickness throughout the entire length.

* Some M14 chromium plated bores had adhesion problems, and that bore is 38% bigger.
 
Cooper called the gun the “poodle shooter” and it was a title he chose after more life experience than any on this board will ever have.

With that being said, their have been some advantages to the Armalite in more recent years that I personally think The Colonel would have been pleased with. But I shall take my rifles in calibers starting with a “3” well before the hot .22 rounds.
 
Once again , I have been educated.!!! It would seem that the archives section has books in it that were written by people who knew about as much as I did:confused:
 
The prototype 1-14 twist was working fine until troop trials in Alaska with extreme cold conditions. The denser air was causing the 55 gr projectiles to destabilize mid-flight. A quick change to 1-12 fixed that problem, at perhaps a slight cost of reduced terminal effectiveness.
I have heard this as well. I wonder if it is true or if there was another reason?
 
The prototype 1-14 twist was working fine until troop trials in Alaska with extreme cold conditions. The denser air was causing the 55 gr projectiles to destabilize mid-flight. A quick change to 1-12 fixed that problem, at perhaps a slight cost of reduced terminal effectiveness.

I have heard this as well. I wonder if it is true or if there was another reason?

That's interesting. I admit, I don't know where or under what conditions the cold weather testing may have been conducted. But, my thought was that the air at -10 F at 300 feet above sea level is going to be a lot more dense than the air at 6200 feet above sea level like where I live. I wonder how nit picky those who made the decisions were.
 
The switch to ball powder also necessitated the first upgrade of the extractor spring. The extractor spring was again upgraded in the M4.

Good stuff, lysander
The extractor spring/extractor spring assembly changed many times over the course of the system.

M16/M16A1 development:

- the original spring
- the improved spring
- the improved spring with the white buffer
- the improved spring with the blue buffer

Then came the M4 with the improved spring and the black buffer.

Then came the M4A1 with the gold spring and the black buffer.
 
I have heard this as well. I wonder if it is true or if there was another reason?
Stability is a bit more complicated than pulling out the Greenhill formula and dropping in some numbers.

The stability of a bullet is dependent on how fast it spins and the lift on the bullet, and the lift is dependent on the velocity. The initial spin is the twist times the velocity. However, velocity drops as the bullet goes down range, but the spin does not drop near as fast. So, bullets get more stable as they move down range.

At zero degrees F the M193 bullet from a 1-14 barrel was unstable for about the first 6 meter of flight (S < 1), after that the the bullet becames stable. With the 1-14 twist barrel initial yaw angels of 20 degrees were seen at 0 F, but by 100 meters the they damped down to 6 or 7 degrees.

The problem wasn't so much keyholing at low temperatures but unacceptable accuracy, as flight at 20 degrees yaw is not conducive for precision shooting. In fact, if the temperature is above 35 F, the stability factor for the 1-14 twist is = 1, and things look good.

Why was this first noted in Alaska in the early 1960 and not earlier?

Oddly enough, because the AR-15/M16 had not been shot much in even mildly chilly weather. Most testers don't like to stand out in freezing weather to watch a rifle shoot 10,000 round from a fixed stand, so they schedule that sort of thing for the spring and summer. Same for the troop trials - Fort Benning in the summer. And, where did Armalite try and sell the AR-15 earlier? South America, the Middle East, Vietnam, and at least once at a Texas barbecue.

Nobody has done a serious accuracy test in cold weather.

(Evaluation Test of the rate of Rifling Twist in Rifle, Caliber .223, AR-15, and Comparison of Exterior ballistics of the M193 Projectile when Launched from 1-12 and 1-14 Twist M16A1 Rifles)
 
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Stability is a bit more complicated than pulling out the Greenhill formula and dropping in some numbers.

The stability of a bullet is dependent on how fast it spins and the lift on the bullet, and the lift is dependent on the velocity. The initial spin is the twist times the velocity. However, velocity drops as the bullet goes down range, but the spin does not drop near as fast. So, bullets get more stable as they move down range.

At zero degrees F the M193 bullet from a 1-14 barrel was unstable for about the first 6 meter of flight (S < 1), after that the the bullet becames stable. With the 1-14 twist barrel initial yaw angels of 20 degrees were seen at 0 F, but by 100 meters the they damped down to 6 or 7 degrees.

The problem wasn't so much keyholing at low temperatures but unacceptable accuracy, as flight at 20 degrees yaw is not conducive for precision shooting. In fact, if the temperature is above 35 F, the stability factor for the 1-14 twist is = 1, and things look good.

Why was this first noted in Alaska in the early 1960 and not earlier?

Oddly enough, because the AR-15/M16 had not been shot much in even mildly chilly weather. Most testers don't like to stand out in freezing weather to watch a rifle shoot 10,000 round from a fixed stand, so they schedule that sort of thing for the spring and summer. Same for the troop trials - Fort Benning in the summer. And, where did Armalite try and sell the AR-15 earlier? South America, the Middle East, Vietnam, and at least once at a Texas barbecue.

Nobody has done a serious accuracy test in cold weather.

(Evaluation Test of the rate of Rifling Twist in Rifle, Caliber .223, AR-15, and Comparison of Exterior ballistics of the M193 Projectile when Launched from 1-12 and 1-14 Twist M16A1 Rifles)

Do you have a link to this study? It’s often discussed but I have never seen any real world evidence presented of this phenomenon of a bullet re-stabilizing after some distance. Personally I would have to see it on high speed camera or shadow graph to believe a bullet could re stabilize from a 20 degree yaw
 
Main reason I use ball powder vs extruded powders for .223 is powder bridging while loading. I can get good loads with appropriate burn rate extruded powders though.
If you use a funnel and drop tube with the extruded powders, things usually go much smoother. I use 4895 for one of my 223 loads, and without that drop tube, I wont get all the powder in the case.

Other than that one load, I normally use 748, which meters so nicely through the powder measures, and makes bulk loading a bit easier. You dont get that "chop" with the ball powders that you do with the extruded powders, and the charges tend to be more consistent.

Cooper called the gun the “poodle shooter” and it was a title he chose after more life experience than any on this board will ever have.

With that being said, their have been some advantages to the Armalite in more recent years that I personally think The Colonel would have been pleased with. But I shall take my rifles in calibers starting with a “3” well before the hot .22 rounds.
Cooper was Cooper, and entitled to his opinions like anyone else, but he was also wrong about a lot of things. If you only blindly follow one master, you tend to miss out on a lot and limit yourself. ;)
 
Do you have a link to this study? It’s often discussed but I have never seen any real world evidence presented of this phenomenon of a bullet re-stabilizing after some distance. Personally I would have to see it on high speed camera or shadow graph to believe a bullet could re stabilize from a 20 degree yaw
Stability is simply the tendency of a object that has been disturbed from a equilibrium position to return to that equilibrium position. With an unstable bullet all this means if there is a yaw induced the angle of the yaw will increase until the bullet begins to tumble.

Here we have a bullet in flight with a yaw angle of alpha (α).

The lift force is = = Cl * A x .5 * ρ x V^2

with

Cl = coefficient of lift
A = reference area
ρ = density of fluid
V = velocity

Since the lift acts through the center of pressure (Cp, red), which is offset from the center of mass (Cg, white) by distance d, the lift produces a moment Mo known as the overturning moment. The overturning moment is what destabilizes the bullet. If the bullet has sufficient spin, the stabilizing moment will counter act the overturning moment and force the yaw angle back to α = 0 (S > 1), if the spin is insufficient (S < 1) the overturning moment will force and increase in α, and at S = 1, the two moments are equal and the yaw angle remains constant. The lift force is dependent on the velocity, as we have seen above, so stability is going to be dependent on the actual velocity of the bullet as well as the spin rate. The forces retarding the spin of a bullet are next to nil, only the friction of the air on the sides of the skin, but the forces retarding the forward velocity of the bullet are great, the shock wave, the pushing of the air out of the path of the bullet, so the velocity drops several orders of magnitude faster that the spin.

A graph of the static stability of an M80 FMJ with respect to range (velocity) showing the initial increase, then decrease as the spin degrades.

How fast the bullet pitches up (unstable) or returns to equilibrium (stable) depends on the distance between the Cp and Cg, the lift force, and the magnitude of the stabilizing moment. So, under the proper conditions, the yaw angle can slowly increase (unstable flight), and as velocity degrades, decrease back into stable flight.

2yBhP31.png

Fzl4oy7.png
VT6KT2F.png
Sd0HsLP.png

As I said in the other post, all this is in Test of the Rate of Rifling Twist in Rifle, Caliber .223, AR-15, and Comparison of Exterior Ballistics of the M193 Projectile when Launched from 1-12 and 1-14 Twist M16A1 Rifles

EDIT:
Don't confuse accuracy or group size with stability.
 
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Stability is a bit more complicated than pulling out the Greenhill formula and dropping in some numbers.

The stability of a bullet is dependent on how fast it spins and the lift on the bullet, and the lift is dependent on the velocity. The initial spin is the twist times the velocity. However, velocity drops as the bullet goes down range, but the spin does not drop near as fast. So, bullets get more stable as they move down range.

At zero degrees F the M193 bullet from a 1-14 barrel was unstable for about the first 6 meter of flight (S < 1), after that the the bullet becames stable. With the 1-14 twist barrel initial yaw angels of 20 degrees were seen at 0 F, but by 100 meters the they damped down to 6 or 7 degrees.

The problem wasn't so much keyholing at low temperatures but unacceptable accuracy, as flight at 20 degrees yaw is not conducive for precision shooting. In fact, if the temperature is above 35 F, the stability factor for the 1-14 twist is = 1, and things look good.

Why was this first noted in Alaska in the early 1960 and not earlier?

Oddly enough, because the AR-15/M16 had not been shot much in even mildly chilly weather. Most testers don't like to stand out in freezing weather to watch a rifle shoot 10,000 round from a fixed stand, so they schedule that sort of thing for the spring and summer. Same for the troop trials - Fort Benning in the summer. And, where did Armalite try and sell the AR-15 earlier? South America, the Middle East, Vietnam, and at least once at a Texas barbecue.

Nobody has done a serious accuracy test in cold weather.

(Evaluation Test of the rate of Rifling Twist in Rifle, Caliber .223, AR-15, and Comparison of Exterior ballistics of the M193 Projectile when Launched from 1-12 and 1-14 Twist M16A1 Rifles)

Thank you for the additional details. Poor accuracy vs complete destabilization are completely different scenarios, but neither would be acceptable in a fielded rifle system.
 
Cooper called the gun the “poodle shooter” and it was a title he chose after more life experience than any on this board will ever have.

With that being said, their have been some advantages to the Armalite in more recent years that I personally think The Colonel would have been pleased with. But I shall take my rifles in calibers starting with a “3” well before the hot .22 rounds.

As much as I like Jeff Cooper, I doubt he has more real world experience with the M16 series of rifles than several of the combat vets on this forum. Though I do believe he has plenty of combat experience with the 1911, as this would have been his primary issue weapon during most, if not all, of his military career.
 
My XM16-E1 had the gold buffer as was a shooter. The only problem was the constant armorer inspections in which they always want to trash it because the bore was pitted. As far as I know the July 67 replacements brought the first reliable rifles to the battalion. Well into 68 every squad had a M14 assigned. I'm not sure when we finally got cleaning gear beyond Luberplate and a tooth brush from the SP pack.
 
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