Gas Port Size vs. Rate of Erosion

[Dionysusigma]

As many know, gas port size is one of the key deciding factors in how "strong" an AR will run - basically, the larger the port, the more gas is utilized to operate the carrier and bolt. Some manufacturers run theirs a bit on the large side to assist in reliability with several different types of ammo, because (for instance) the pressures of Russian-manufactured ammo run lower than Winchester Q3131, but a larger port ensures that even the weaker ammo can still operate the system as well as the hotter ammo can.

What I'm wondering is this: Is there a correlation between gas port size and rate of gas port erosion? Basic physics state that the larger the hole a fluid is passed through, velocity decreases while pressure increases, and reverse for vice versa, (given the same energy). So does this mean that larger gas ports erode faster than small ones (including other factors like the greater initial surface area of the port)?

In short: is it pressure, or velocity, that causes erosion? :confused:

PS Or is throat erosion a bigger issue?

PPS Am I just overthinking this?

[MarkG]

As many know, gas port size is one of the key deciding factors in how "strong" an AR will run - basically, the larger the port, the more gas is utilized to operate the carrier and bolt. Some manufacturers run theirs a bit on the large side to assist in reliability with several different types of ammo, because (for instance) the pressures of Russian-manufactured ammo run lower than Winchester Q3131, but a larger port ensures that even the weaker ammo can still operate the system as well as the hotter ammo can.

What I'm wondering is this: Is there a correlation between gas port size and rate of gas port erosion? Basic physics state that the larger the hole a fluid is passed through, velocity decreases while pressure increases, and reverse for vice versa, (given the same energy). So does this mean that larger gas ports erode faster than small ones (including other factors like the greater initial surface area of the port)?

In short: is it pressure, or velocity, that causes erosion? :confused:

PS Or is throat erosion a bigger issue?

PPS Am I just overthinking this?

Yes...

The SEARCH BUTTON (https://www.google.com/search?q=gas+port+erosion+site%3Am4carbine.net&hl=en&biw=1399&bih=775&num=10&lr=&ft=i&cr=&safe=off) is a beautiful thing.

[Dionysusigma]

Ah. http://www.armedpolitesociety.com/Smileys/default/smack.gif I should've thought of that first, of course. :blink:

Was wondering because a particular pinned 14.5" upper receiver group that I was thinking of SBRing later and running almost exclusively suppressed uses a gas port with diameter of .750, and was concerned about the port opening up too far in a much, much shorter period of time than one that was intended from the get-go for CQB/suppressed use.

[Robb Jensen]

It's the heat from the pressurized gas which erodes the port. The shorter the length of the gas system the higher the level and faster the rate of erosion (higher heat and more gas). Also suppressed magnifies the problem since more gas is going through the system. Softer barrel steels erode faster than harder better steels.
Like magazines do not fall in love with your barrels. They wear out like anything does. If you wear out barrel replace it. Good barrels cost about the same as 1K rounds of good ammo, don't overthink this.

Personally I purpose build my own guns for suppressed only or use the excellent Noveske switch block gas block.