Originally Posted by
Clint
Chamber pressure has a curve during firing.
This curve includes both the time the projectile is in the bore and time it takes for residual pressure to blow down after the projectile has exited the bore.
The total impulse or area under the curve determines the ability of the pressure to do work, such as accelerate the projectile or cycle the action.
The area under the curve is really a summation (integration) of the pressure at each instant, or to state it simply, PRESSURE X TIME.
In a straight blowback weapon, the entire pressure curve is used to power the action.
In a gas operated, locked breech weapon, placement of the gas port relative to the muzzle determines which later portion of the pressure curve is used to power the action.
A port placed at the muzzle (i.e. gas trap) uses only residual pressure, while a port placed at the case mouth uses the entire curve.
Obviously, a port placed somewhere in the middle uses uses a combination.
Once a portion of the curve is selected by the port placement ( the Available Gas Drive ), the port size scales that down to the Actual Gas Drive used to power the action.
There are many combinations of port placement and size that can all yield the same total number for Gas Drive at the front end of the system.
If this was a simple system, you could select any of these combinations and they would produce identical results at the back end of the system.
But it's not, and they don't.
So I’ll resurrect this to ask…
What is the minimal distance from port to muzzle that is reliable? I’ve seen various Dissipator configs with seemingly different lengths past the port.
Does this change based on gas system length or port size?
"An opinion solicited does not equal one freely voiced," Al Swearengen, Deadwood 1877.
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