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Comment by Thorrez | Hacker News Reader

The entire point of this article is the difference between the AR-15 and the M-16. So if they are essentially the same, that means this article is pointless. That type of assertion needs some strong evidence given how well-researched the article is.

The 3 differences the article lists between the AR-15 and the M-16 are:

1. The M-16 added a useless "manual bolt closure" making it a bit heavier.

2. The M-16 rate of twist was changed from one-in-14-inches to one-in-12, which made it 40% less lethal.

3. The M-16 switched from IMR 4475 powder to ball powder, which made it much much less reliable. After tons of US soldiers died due to the unreliability, they modified the ball powder and changed the mechanical "buffer" of the rifle, which made it more reliable, but still less than the AR-15.

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The manual bolt closure is far from useless in a military context and has two common real-world use cases today that I am aware of.

The increase in twist was because the rifle failed to stabilize bullets in some environments during testing, which is a pretty gross defect. And higher twist rates don't decrease lethality, it is actually the opposite for well-understood reasons. Current barrels are 1-in-9 IIRC.

The switch to ball powder happened after the initial usage of the M-16, which is correctly characterized as a logistical screwup, and they ended up redesigning the rifle so that it would perform correctly with the ball powder.

It wouldn't stabilize tracer rounds, it was perfectly fine with standard issue rounds. The manual bold close wasn't in Stoners original design, it was requested by the military. In my opinion the internal piston design is the true genius of this rifle. Recoil is almost straight back so follow up shots are much easier.

As the Russians seem to be moving to 5.56 the American military is looking to move to the 6mm class.

M4 barrels are 1:7. Civ rifles seem to be 1:7 to 1:9. (civ are more likely to use 55gr still; military is 62gr, and there are people using 77gr...)

I hate the forward assist, but not enough to delete it. I mostly use an X95 SBR (13") now, though.

"The manual bolt closure is far from useless in a military context and has two common real-world use cases today that I am aware of."

What are they?

It allows you to manually (re)load and arm the rifle very quietly; the normal charging action to chamber the first round in a magazine is quite loud and recognizable. Useful for stealth. And if you accidentally get a ton of dirty in the action when the bolt locks back i.e. when the magazine is empty, you can force the first cartridge on a new magazine to chamber through the dirt (the first shot will usually clear the dirt out of the critical areas).

Failure to stabilize the bullet was a feature, not a defect. At close range that unstable bullet had more killing power (Assuming fmg, not civi rounds). Increasing the twist extended range but sacrificed effectiveness at likely combat distances.

Stability in the air (external ballistics).

Yup. And flying slightly off-axis means greater chance of tumbling as you enter a soft target. It is the one time you dont want to be flying strait.

You do understand that nearly all the parts on an M16 are interchangeable with an AR15, right? The AR15 is an M16 without select fire capability.

There are two different AR-15s: ArmaLite AR-15 which is what the article is about and from which M16 was derived and then modern day Colt AR-15 which is civilian version of M16.

There are a hundred (at least) vendors who make AR-15 pattern rifles, Colt's patent expired several years ago.

The Armalite AR-15, the Colt AR-15, the Colt M4, Colt M4A1, FN M4A1, and the military M16, M16A1, M16A2, are all the same weapon with minor modifications. The significant differences are barrel length (interchangeable among most if not all), upper (slick side or with forward assist, not consistent among any of them), buffer weight (generally the full-auto versions have a heavier buffer), trigger model (full auto, 3rd burst, and semi-only -- many variants exist and are interchangeable among most models w/ exception that the civilian models do not have the upper hole that allows for the full-auto trigger components to be installed).

My point was that the fact that Colt markets what is essentially demilitarized M16 as "The AR-15(TM)" is source of significant confusion.

The forward assist is critical in a rifle of the AR-15 design. Otherwise you cannot recover from some failure modes without taking the rifle apart.

The rate of twist varies to stabilize whatever round is most commonly used. 1-7 and 1-9 are commonly used today due to bullet weight.

Powder was an issue in the original issue Vietnam era M16.

The manual bolt closure is an absolute necessity. Unless you don't mind having your bolt stuck open while under fire...

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