Gas port erosion with different barrel profiles

[ether]

Is there any evidence that thinner profile barrels exhibit port erosion any sooner than thicker barrels? I did search on port erosion and did not find my answer.

[ICANHITHIMMAN]

I'm going to try this again, running on the assumption that MistWolf has located her medication by now.

Is there any evidence that thinner profile barrels exhibit port erosion any sooner than thicker barrels? I did search on port erosion and did not find my answer.

I think that's an insult, do you mean throat erosion and barrel length?

[ether]

Will a 14.5" pencil barrel port erode any faster than a 14.5" M4 barrel port?

[ICANHITHIMMAN]

Will a 14.5" pencil barrel port erode any faster than a 14.5" M4 barrel port?

Again are you talking about the throat? I have never heard of a gas port eroding. So my answer yes and no

I just read through all your post expect to see this closed to

[SMT85]

what ether is asking is if the gas port on a .625 barrel thickness under the gas block erodes quicker than .750 barrel thickness under the gas block due to less wall thickness of the barrel.

pencil vs govt/m4 profile

sorry. i do not know the awnser i but am curious as well if it's possible.

[Iraqgunz]

Next time instead of insulting a member and showing your ass (by admitting you were too lazy to use the SEARCH feature) try doing exactly that.


I'm going to try this again, running on the assumption that MistWolf has located her medication by now.

Is there any evidence that thinner profile barrels exhibit port erosion any sooner than thicker barrels? I did search on port erosion and did not find my answer.

[ICANHITHIMMAN]

what ether is asking is if the gas port on a .625 barrel thickness under the gas block erodes quicker than .750 barrel thickness under the gas block due to less wall thickness of the barrel.

pencil vs govt/m4 profile

sorry. i do not know the awnser i but am curious as well if it's possible.

I know what he is asking, I am trying to get him asking the right question he is worrying about something that is not going to be an issue at all before the throat is worn out. When a barrel is shot out its not the rifling or the gas port its the throat.

[SMT85]

I know what he is asking, I am trying to get him asking the right question he is worrying about something that is not going to be an issue at all before the throat is worn out. When a barrel is shot out its not the rifling or the gas port its the throat.

sorry brother, was just trying to help him out.

[michael word]

I think the barrel steel and chrome plating quality play a larger roll than the thickness of the barrel. If you, however, do alot of mag dumps the thinner barrel will most likely wear in all areas faster than a thicker barrel because of the increased heat. Gas port erosion is a non-issue with most guns, unless you are shooting for absolute accuracy.

[Magic_Salad0892]

I know what he is asking, I am trying to get him asking the right question he is worrying about something that is not going to be an issue at all before the throat is worn out. When a barrel is shot out its not the rifling or the gas port its the throat.

This isn't true in every case. To the best of my knowledge.

You know Andrew's 40K round test that's been passed around lately?

The "Federal Barrel" only had 10k in it, and the gas port had showed erosion. The rifling and all is still intact. Now he didn't measure the leade, or throat (I wish he would have, and I've thought of contacting him about it.) but I'd be willing to bet that at 10k rounds it would have been mostly intact.

Also. I do think barrel thickness makes a difference. But I don't know how measurable. And I think it'd have to be a more extreme example to measure it properly. Like SOCOM profile against LW. Not M4 profile.

Assuming both barrels were shot using the same ammo, under similar conditions, and were made the same way, by the same maker, and of the same barrel length.

[ICANHITHIMMAN]

This isn't true in every case. To the best of my knowledge.

You know Andrew's 40K round test that's been passed around lately?

The "Federal Barrel" only had 10k in it, and the gas port had showed erosion. The rifling and all is still intact. Now he didn't measure the leade, or throat (I wish he would have, and I've thought of contacting him about it.) but I'd be willing to bet that at 10k rounds it would have been mostly intact.

Also. I do think barrel thickness makes a difference. But I don't know how measurable. And I think it'd have to be a more extreme example to measure it properly. Like SOCOM profile against LW. Not M4 profile.

Assuming both barrels were shot using the same ammo, under similar conditions, and were made the same way, by the same maker, and of the same barrel length.
Not saying your wrong, just never heard of it.

[markm]

I bet it's negligible... but I could see how a full profiled barrel would absorb more heat and have the potential for a slight reduction in port errosion.

[samuse]

I've always been curious about this too.

What wears faster?

.625" @ gas port or .750" @ gas port?

Assuming same ammo, rate of fire, etc...

[Krusty783]

I've always been curious about this too.

What wears faster?

.625" @ gas port or .750" @ gas port?

Assuming same ammo, rate of fire, etc...

Given that the gas port and gas block functional assembly is the same for each barrel profile, they should have similar erosion rates. It should be noted that not all gas ports are the same size and smaller ports should exhibit higher gas velocities and thus slightly faster erosion. Even though the material removal rates may be similar, a gov't profile barrel has a .0625" wear advantage on a pencil barrel, so it will last longer.

There would probably be less erosion if the port was finished with a slight countersink or radius, but that would add an extra machining operation.

-Hold the phone- are we talking erosion within the bore or at the gas block to barrel interface?

[samuse]

Given that the gas port and gas block functional assembly is the same for each barrel profile, they should have similar erosion rates. It should be noted that not all gas ports are the same size and smaller ports should exhibit higher gas velocities and thus slightly faster erosion. Even though the material removal rates may be similar, a gov't profile barrel has a .0625" wear advantage on a pencil barrel, so it will last longer.

There would probably be less erosion if the port was finished with a slight countersink or radius, but that would add an extra machining operation.

-Hold the phone- are we talking erosion within the bore or at the gas block to barrel interface?

I was talking about gas port erosion.

Will the gas port on the heavier section (.750" OD @ FSB)of an M4 barrel be less prone to wear (given all other factors being equal) than the same gas port on a light (.625 OD @ FSB) barrel.

Does the wall thickness matter?

[ether]

I appeciate the thoughtful replies and discussion. SMT85 has me right...and I was mainly wondering about any erosion difference on the bore side of the port between .625" barrels and .750" barrels of the same length. It sounds like it should be negligible in the grand scheme, with throat erosion maybe even negating the concern at that high of a round count.

Also, anyone know if port diameters vary between .625" and .750" barrels with the same length and port location?

ETA: I sincerely apologize to the board and to MistWolf for my behavior...we have enough enemies lately without fighting amongst ourselves over the trivial stuff, and I'm sorry I engaged on that level.

[SteveS]

Being in the profession I Was in,,,how much erosion will cause a failure and what will erosion cause? Higher operating [bolt] pressure or will the erosion cause accuracy problems from barrel wear in the area? Guns are a machine and machines wear out and "hopefully not" break.

[ether]

SteveS - Check out the video link in this thread that Magic referred to:

http://m4carbine.net/showthread.php?t=120917&highlight=40%2C000

Although this was more indicative of a torture-test case than a long-term use case, I was pretty surprised by the visible amount of gas port erosion that these 10K barrels exhibited.

Your question is a really good one though, if I understand it - would gas port erosion start to affect reliability before throat erosion ever would? We know throat erosion can ruin barrel accuracy, but how long will the weapon keep firing reliably until gas port erosion gets the best of it, and reliability is affected?

[Magic_Salad0892]

Not saying your wrong, just never heard of it.

I know. I wasn't calling you out or anything. I was just providing my point of view.


I bet it's negligible... but I could see how a full profiled barrel would absorb more heat and have the potential for a slight reduction in port errosion.

Agreed. Negligible. But I think it's there.

[markm]

Your question is a really good one though, if I understand it - would gas port erosion start to affect reliability before throat erosion ever would?

Nope. The port erodes at the bottom... the top of a high round count barrel still has about the same diameter it always had and thus the gas flow isn't really changing.

[MistWolf]

I sincerely apologize to the board and to MistWolf for my behavior...

Apology accepted and appreciated. Think nothing more of it


...If you, however, do alot of mag dumps the thinner barrel will most likely wear in all areas faster than a thicker barrel because of the increased heat...

With the same round count in the same amount of time, the heat is actually the same. What differs is the thinner barrel (in this case means lesser mass) has less material with which to absorb the heat and less surface for dissipation. With the same amount of heat (BTUs) the barrel with less mass will reach a higher temperature.

Think of the barrel of a rifle like, well a barrel. Take a 50 gallon barrel and cut a 2 inch diameter hole in the bottom, then take say a 25 gallon barrel with a 1 inch hole in the bottom. (We put a larger drain in the 50 gallon barrel because the larger diameter rifle barrel has more surface with which it can "drain" the heat.) Now fill both with water at a rate of 5 gallons per second. The 25 gallon barrel will fill up faster, and you will have to stop more often to wait for it to drain before adding any more water without it overflowing. The 55 gallon barrel will take longer to fill and drains at a slightly faster rate but will have more water to drain before it's completely empty. It's the same with rifle barrels and heat.

What erodes the gas port is gas velocity, density and temperature. High velocity gas cuts very well and when the steel gets hot, it is less resistant to gas cutting. (Gas leaking pas a bullet is also gas cutting and contributes to the wear of the bore.)

The reason there is no gas cutting on the opposite side of the port is due to the reduction of the gas velocity. The gases enter the port at supersonic speeds but in passing through the port, which is a venturi, the velocity is reduced to sub-sonic speeds. (Supersonic speed fluids passing through a venturi behave differently than subsonic speed fluids.)

So, a thinner barrel at the gas port may be more susceptible to port erosion if the thinner material leads to higher temperatures at that location. Also, a barrel thicker at the port will have more material to cut through before enlarging the diameter on the opposite side.

It's also possible that distance of the port from the chamber would have even a greater affect. The closer to the chamber, the higher the temperature and the greater the density of the gases hitting the port

[Magic_Salad0892]

With the same round count in the same amount of time, the heat is actually the same. What differs is the thinner barrel (in this case means lesser mass) has less material with which to absorb the heat and less surface for dissipation. With the same amount of heat (BTUs) the barrel with less mass will reach a higher temperature.

Think of the barrel of a rifle like, well a barrel. Take a 50 gallon barrel and cut a 2 inch diameter hole in the bottom, then take say a 25 gallon barrel with a 1 inch hole in the bottom. (We put a larger drain in the 50 gallon barrel because the larger diameter rifle barrel has more surface with which it can "drain" the heat.) Now fill both with water at a rate of 5 gallons per second. The 25 gallon barrel will fill up faster, and you will have to stop more often to wait for it to drain before adding any more water without it overflowing. The 55 gallon barrel will take longer to fill and drains at a slightly faster rate but will have more water to drain before it's completely empty. It's the same with rifle barrels and heat.

What erodes the gas port is gas velocity, density and temperature. High velocity gas cuts very well and when the steel gets hot, it is less resistant to gas cutting. (Gas leaking pas a bullet is also gas cutting and contributes to the wear of the bore.)

The reason there is no gas cutting on the opposite side of the port is due to the reduction of the gas velocity. The gases enter the port at supersonic speeds but in passing through the port, which is a venturi, the velocity is reduced to sub-sonic speeds. (Supersonic speed fluids passing through a venturi behave differently than subsonic speed fluids.)

So, a thinner barrel at the gas port may be more susceptible to port erosion if the thinner material leads to higher temperatures at that location. Also, a barrel thicker at the port will have more material to cut through before enlarging the diameter on the opposite side.

It's also possible that distance of the port from the chamber would have even a greater affect. The closer to the chamber, the higher the temperature and the greater the density of the gases hitting the port

Thanks for this explanation, MistWolf.

[michael word]

Apology accepted and appreciated. Think nothing more of it



With the same round count in the same amount of time, the heat is actually the same. What differs is the thinner barrel (in this case means lesser mass) has less material with which to absorb the heat and less surface for dissipation. With the same amount of heat (BTUs) the barrel with less mass will reach a higher temperature.

Think of the barrel of a rifle like, well a barrel. Take a 50 gallon barrel and cut a 2 inch diameter hole in the bottom, then take say a 25 gallon barrel with a 1 inch hole in the bottom. (We put a larger drain in the 50 gallon barrel because the larger diameter rifle barrel has more surface with which it can "drain" the heat.) Now fill both with water at a rate of 5 gallons per second. The 25 gallon barrel will fill up faster, and you will have to stop more often to wait for it to drain before adding any more water without it overflowing. The 55 gallon barrel will take longer to fill and drains at a slightly faster rate but will have more water to drain before it's completely empty. It's the same with rifle barrels and heat.

What erodes the gas port is gas velocity, density and temperature. High velocity gas cuts very well and when the steel gets hot, it is less resistant to gas cutting. (Gas leaking pas a bullet is also gas cutting and contributes to the wear of the bore.)

The reason there is no gas cutting on the opposite side of the port is due to the reduction of the gas velocity. The gases enter the port at supersonic speeds but in passing through the port, which is a venturi, the velocity is reduced to sub-sonic speeds. (Supersonic speed fluids passing through a venturi behave differently than subsonic speed fluids.)

So, a thinner barrel at the gas port may be more susceptible to port erosion if the thinner material leads to higher temperatures at that location. Also, a barrel thicker at the port will have more material to cut through before enlarging the diameter on the opposite side.

It's also possible that distance of the port from the chamber would have even a greater affect. The closer to the chamber, the higher the temperature and the greater the density of the gases hitting the port

Exactly what i was getting at, just in less words. Good explination. However, I have to disagee of the heat disipation. The larger barrel will take longer to cool due to the increased mass than the thinner barrel. I experience this at work every day as a machinist working on everything from 2-8" diameter pipe. The larger the pipe, the longer I have to wait before I can continue to the next step.

[MistWolf]

You are correct that the temperature of the larger barrel will take longer to cool to room temperature than the smaller. The reason is because it contains more heat (more BTUs). Because the larger diameter barrel has more surface, it will radiate the heat faster than the smaller one, but because it takes more BTUs (more heat) to reach the same temperature, it will take more time to shed that heat, just as it took more time to reach that temperature.

It's also about surface to mass ratio. Take a piece of aluminum foil, lay it flat in the oven and heat it to 450 degrees and it will heat up right away and cool off right away. Ball it up and do the same thing, it will take more time to heat up and cool off although it has absorbed the same amount of BTUs to bring it's mass to the same temperature

You also know that the smaller pipe when you machine it takes less heat before it gets hot. That's because the smaller pipe has less mass to absorb the BTUs. That's why you can heat a paperclip with a cigarette lighter until it turns cherry red. But if you had a 1 lbs cube of the same material and took the same lighter to it, the best to hope for would be to make it warm to the touch.

I'm not trying to tell you that you don't know your stuff, because it's obvious that you do. Just trying to shed light on how heat (BTUs) and mass affect temperature

[ether]

You are correct that the temperature of the larger barrel will take longer to cool to room temperature than the smaller. The reason is because it contains more heat (more BTUs). Because the larger diameter barrel has more surface, it will radiate the heat faster than the smaller one, but because it takes more BTUs (more heat) to reach the same temperature, it will take more time to shed that heat, just as it took more time to reach that temperature.

So I'm thinking that a pencil barrel could arguably be the best "all-around" barrel for semi-auto-only applications, as long as you aren't torturing it like in the 40K video. In an everyday utilitarian situation, your firing is likely more sporadic than sustained. Port erosion should be negligible. The barrel is getting hotter faster, but it's not insulating that heat as much in the bore, and it's cooling off faster on both the inside and outside of the barrel...ideal in case you need to shoulder the weapon and move around...not to mention the weight savings which go without saying...

[michael word]

correct.

[MistWolf]

Bottom line-

Fire 30 shots in thirty seconds with a pencil barrel
Fire 30 shots in thirty seconds with a heavy profile barrel.
Both barrels will absorb the same amount of heat. Take the temperature of both. The pencil barrel will have a higher temperature. The heavy barrel will cool to ambient temperature a little faster because it has greater surface to radiate the heat.

Now-

Fire one round per second in both barrels until both barrels reach 200 degrees. The pencil barrel will reach 200 degrees with fewer shots fired than the heavy barrel. The pencil barrel will also cool faster than the heavy barrel because it is holding less heat.

Both barrels will radiate heat inside the bore. That's why knowledgeable shooters will put their rifles aside with the bolt open and the muzzle up (or down) to let air flow through the barrel to aid in cooling

[ether]

Cool, I have my answer. I really am sorry for the way I started this thread, but in spite of me it turned out to be one of the more informative I can recall...many thanks all.