Why the buffer tube?

halfmoonclip said:

Is it peculiar to the AR platform? And for what reason?
Never heard of it in any other platform,…

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No, it happens with many firearms. Very common with blow backs.

d2wing said:

One reason is that the inline system makes the AR the most accurate semiautomatic centerfire rifle in use.

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Completely false. The bullet is long gone by the time any of that happens.

The AR got accurate because gobs of money were spent over the years to make them accurate and proliferate the tooling to do so. In addition to even more money spent on accurate ammunition.

Basicly nobody scoped ARs for accuracy in the 1980s. The Mini-14 was what you bought if you wanted a scoped 223 autoloader back then.

Crosshair said:

The bullet is long gone by the time any of that happens.

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Rather, in fact, it is THIS statement which is “completely false.”

The carrier starts moving as soon as the rear edge of the bearing surface clears the rear edge of the gas port. That’s how physics works.

Varminterror said:

Rather, in fact, it is THIS statement which is “completely false.”

The carrier starts moving as soon as the rear edge of the bearing surface clears the rear edge of the gas port. That’s how physics works.

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No. That's not how physics works. At all.

The shockwave of gas takes time to overcome inertia and make a 180 degree turn into the gas tube. It then takes additional time to travel down the gas tube. All the while being slowed by friction against the side of the gas tube.

Once it finally gets into the carrier, it takes time to pressurize and overcome the inertia of the carrier to begin traveling rearward.

The inertia of the high pressure gas keeps the gas tube pressurized after the pressure in the barrel has dropped. Again, taking time to do a 180 degree turn. ( I don't actually know if the gas flow ever actually reverses in the gas tube.)

This inertia of gas is how internal combustion engines scavenge the cylinders during the exaust/intake stroke, with both the exhaust valve and the intake valve open at the same time.

Granted this all takes less time than what we can perceive, but it still takes some time and is not instant. If it was, what would be the point of pigtail gas tubes?

If you have 100' of air hose connected to a 100 PSI air tank and open the valve, does the far end of the hose immediately have 100 PSI of air pressure? No. It takes time for the gas to flow down the hose. The same thing happens in a gas operated firearm, just much faster.

@Crosshair - that all sounds great, but it's been disproven time and time again.

The reciprocating mass of the AR IS accelerating while the bullet is in the bore. You're not the first guy to be wrong about this, and unfortunately, you're likely not the last - but a lot of us sure wish you were.

Crosshair said:

Completely false. The bullet is long gone by the time any of that happens.

The AR got accurate because gobs of money were spent over the years to make them accurate and proliferate the tooling to do so. In addition to even more money spent on accurate ammunition.

Basicly nobody scoped ARs for accuracy in the 1980s. The Mini-14 was what you bought if you wanted a scoped 223 autoloader back then.

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You must have missed the video. You misunderstand how it works among other things. Recoil is immediate. The inline system means that the stock is not a pivot point as it is on other rifles. The muzzle does not immediately climb like other rifles. Also the M-16 was very accurate from the beginning. I qualified expert easily in 1969. Scopes have nothing to do with the inherent accuracy of the M-16. Your comments about gobs of money and tooling spent solely to make them accurate is also false. Gobs of money possibly were spent because the military wanted other versions for other purposes than it was designed for.

Ignition Override said:

Maybe Stoner somewhat copied the concept used by Vorgrimmler in Spain, used in the CETME, then H&K G3 etc.

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Well, where else was he going to put the spring?

Actually, he was influenced by Melvin Johnson:

I will explain again, recoil is generated the instant the primer ignites the powder and the bullet starts to move. Physics states that for each action, there is an equal and opposite reaction. Movement of the bolt and the force of the gas is actually a diversion of force which absorbs some of the recoil and spreads it out. Movement of the weapon is caused by firing the bullet regardless of the bolt movement.
In the AR, the movement is straight back to the buttstock. A normal stock is offset below the recoil force causing muzzle rise as the butt is a pivot point. I hope this helps. It is what makes the AR more accurate in single fire as well as full automatic fire.

halfmoonclip said:

Hmmmm. Varminterror, I liked your first explanation better; nothing happens 'till the bullet passes the gas port. I concur that the gas doesn't arrive in the carrier key instantly, but the lag is so slight as to be imperceptible.
Straight blowbacks are a little more complicated; there is an equal and opposite action, but the bolt, being much heavier, really doesn't move (much) until the bullet is gone.
The AR platforms straight line design does change its reaction to recoil. It wasn't altogether a new idea, but it has certainly prospered. Stoner was thinking outside the box as regards layout and materials.
Moon

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Again you miss the point. Recoil and weapon movement is not caused by the bolt. The statement that nothing happens until the bullet passes the gas port is wrong regarding recoil.
I am wondering how you came up with that. If that were the case bolt action rifles would not recoil at all.

Personally I think the buffer tube setup is pretty light, simple and effective, impessive considering it's a design from a time before seat belts were standard eqiupment.
I remember changing a lower on one of my 7.62x39 ARs from a carbine buffer tube with a 5.1 oz buffer to an A2 stock & 5.2 oz buffer. The rifle length stock was a Hogue so it was about as light as a std. M4 stock. The recoil impulse felt a bit smoother with the rifle length buffer setup vs a carbine length. It was noticeable enough I eventually swapped a few more of my ARs from carbine to rifle buffers.

d2wing said:

The statement that nothing happens until the bullet passes the gas port is wrong regarding recoil.

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There was no claim that recoil did not start until the gas system is pressurized - it’s the internet, you can’t fabricate delusions to try to move the goal post after you’ve failed to support a false claim.

Varminterror said:

The carrier starts moving as soon as the rear edge of the bearing surface clears the rear edge of the gas port.

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Varminterror said:

There was no claim that recoil did not start until the gas system is pressurized - it’s the internet, you can’t fabricate delusions to try to move the goal post after you’ve failed to support a false claim.

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I agree I think. I hope you don't think that I made a false claim.

Varminterror said:

The carrier starts moving as soon as the rear edge of the bearing surface clears the rear edge of the gas port.

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Actually, there is a delay of about 1/4 milliseconds for the gas pressure to fill the gas tube, and begin pressurizing the carrier cavity.

T= 0 is primer ignition, the gas port is uncovered at approximately .7 ms for the M16 and .4 ms for the M4



Pressure can only move so fast, the speed of sound . . .

d2wing said:

A normal stock is offset below the recoil force causing muzzle rise as the butt is a pivot point.

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That depends on the design of the stock . . .





In reality, most muzzle rise is due to your shoulder and body moving, these things also had muzzle rise even though the theoretical thrust line of the recoil was centered in the shoulder.

Note that the M79 has a slight jump upwards

lysanderxiii said:

That depends on the design of the stock . . .

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Now those are funky!