How Does The Bolt Unlock?

[17K]

So basically the buffer is the most influential piece of the puzzle in regards to the rearward part of the cycle?

[Failure2Stop]

So basically the buffer is the most influential piece of the puzzle in regards to the rearward part of the cycle?

Of the things that you can easily change in the back of the gun, yes.
But altering the mass of the carrier, changing the cam, changing the vent hole position/size, hammer shape, and overall stroke length could individually significantly alter the operation as well.
But those things would be a dedicated effort rather than simply swapping buffers or springs.

[Clint]

To put a fine point on it.

The spring is almost irrelevant in the initial part of the cycle leading up to start of extraction from 0 to ~2.5ms.

This initial part of the cycle is dominated by mass and gas.


The remainder of the cycle from extraction to the end of carrier travel from 2.5 to 20 or 30ms is the spring absorbing and storing the initial energy of the BCG.

This part of the cycle is dominated by mass and spring, with some friction thrown into the mix.

So basically the buffer is the most influential piece of the puzzle in regards to the rearward part of the cycle?

[lysander]

So basically the buffer is the most influential piece of the puzzle in regards to the rearward part of the cycle?

Assuming the gas port size remains the same.

[prepare]

VLTOR has done some interesting engineering in regards to their A5 Buffer System;

One of the other unique features about the A5 buffers are their "internal biasing springs". There’s a spring inside of each buffer that keeps internal weights stacked against the front face of the buffer. This assures that the weights are always in the same place when the gun starts its unlocking and cycling processes. Weights are always in the same position, so the gun is always overcoming the same mass, in the same way, every time.

Whether you’re using the carbine buffer system, or the longer rifle buffer system, the bolt carrier’s stroke length is the same – around 3.75”. The carrier travels the same distance, so the amount of compression a carbine spring and rifle spring experience is the same.
However, the carbine spring is shorter and has less wire than a rifle buffer spring. This means with the rifle buffer system, you have a longer spring with more coils and more wire to perform the same work. When both springs are deflected the same amount, the carbine spring experiences more stress, and also experiences a higher differential between the pre-loaded position and fully-loaded positions than a rifle spring does.

[lysander]

One more thing about gas port sizing . . .

Increasing the size of the port, does more than just increasing the pressure in the gas tube, it changes the timing of the system.

The larger the port, the faster gas moves into the front end of the gas tube, the faster in the front, the faster out the back and into the cavity, so everything shifts left.

If you gas port is "oversized" adding buffer weight will reduce the speed, but it may not restore the timing.

[prepare]

The timing seems to be somewhat forgiving though given that variation (usually bigger) between gas port sizes.

For example, if a .062 gas port for a 14.5 is optimal a .061-.065 would probably be imperceptible and run fine correct?

[lysander]

Plus 0.001" is probably "negligible", as that is the tolerance on the gas port.

Whether one drill size up, or down is "imperceptible", I won't say, as one drill size is sometimes the difference between working and not working.