After you pull the trigger

[ALCOAR]

,,,,,,,,,,

[markm]

That's my own vise. $20 swap meet purchased 20 years ago.

[Sgt_Gold]

PigTail and expansion chamber gas tubes attempt to
fool the rifle into thinking that the gas port is,
located further away that it really is, but they are
not as good of a solution as actually moving the gas
port out...

Do you know why this is?

If you want to lower the pressure in the gas system of a weapon, you increase the volume of the gas system itself. A pig tail or expansion chamber in the gas system increases the volume of the system, and that lowers the pressure of the gas in the system.

[lifebreath]

Port size does not regulate pressure into the gas tube. It regulates flow (CFM, or Cubic Feet Per Minute) which determines how quickly the system fills and comes up to pressure.

It regulates pressure indirectly by its relationship to the dwell time, which is dependent on the length of the barrel after the port. For example, if the port it too small, enough pressure does not build up before the bullet exits the barrel. Conversely, if the barrel is short and dwell time is short, the port needs to be opened larger to allow a faster flow of gas into the system to get the pressure up to the required level before the bullet exits the barrel.

[MistWolf]

If you want to lower the pressure in the gas system of a weapon, you increase the volume of the gas system itself. A pig tail or expansion chamber in the gas system increases the volume of the system, and that lowers the pressure of the gas in the system.

The increase in volume using a pigtail in a gas tube is very small. Expanding the internal diameter of the gas tube will have a larger effect. It's possible either change will not have a practical effect in pressure or dwell time. Either way, it's purely theoretical speculation until it's proven by math and/or the change in results are measured

It regulates pressure indirectly by its relationship to the dwell time, which is dependent on the length of the barrel after the port. For example, if the port it too small, enough pressure does not build up before the bullet exits the barrel. Conversely, if the barrel is short and dwell time is short, the port needs to be opened larger to allow a faster flow of gas into the system to get the pressure up to the required level before the bullet exits the barrel.

That's what I said. Port size controls flow (CFM) which determines how fast the system comes up to pressure, not how much pressure will be allowed into the system. If the system were closed, gas would flow through the port until pressure was equal on both sides. A pressure regulator would only allow gases to flow through until the pressure on the outflow side reached a predetermined level

[MarkG]

Pressure from the port is regulated only by the size of the gas port and the diameter of the barrel.

Enlarging the gas port increases VOLUME, not pressure.

[TooTall]

Enlarging the gas port increases VOLUME, not pressure.

Yes, that makes sense, but if the volume of gas that flows through the port is limited by the diameter, wouldn't that in turn affect the overall pressure?
In other words, if the pressure in the barrel is 10,000 PSI at the port location, but the gas system is fed by a tiny hole for a very short time, would the gas system actually see the same 10,000 PSI ?

[MistWolf]

Yes, that makes sense, but if the volume of gas that flows through the port is limited by the diameter, wouldn't that in turn affect the overall pressure?
In other words, if the pressure in the barrel is 10,000 PSI at the port location, but the gas system is fed by a tiny hole for a very short time, would the gas system actually see the same 10,000 PSI ?

Port size controls volume flow (usually expressed in Cubic Feet per Minute) only. What controls pressure is the BCG. Once the pressure inside the BCG reaches a certain point, it begins moving until exposing the vent holes and dumps the pressure overboard

[ForTehNguyen]

Yes, that makes sense, but if the volume of gas that flows through the port is limited by the diameter, wouldn't that in turn affect the overall pressure?

pressure would be the same, just more gas of that same pressure will flow through.

[TooTall]

Can anyone recommend some really good books on internal ballistics and on designing semi auto guns?
I have a pdf of Theory of the Interior Ballistics of Guns, by J. Corner.
(I just recently got it and havent read it yet, but it was recommended.)
Any other titles I should look for?