High Velocity Throat Erosion

[bigngreen]

Over the years borescoping guns I think there are a couple different types of wear, you'll the blow torch effect that will start at any edge and they fire crack stuff and you'll see just wear I think from the powder.
Where the cone point is coming of the shoulder does change thing BUT it's not like doubling your life or something extreme but if you can keep the cone point on hotter chambering in the neck it does seem to take something from the throat.
Unburnt powder gets blasted out of the case and we know that if you focus anything at speed even water it will cut or abrade and I think it does contribute, I've scoped a number of barrels that were ran with N570 and they were toast in a well maintained rifle in 300 rounds for a 338 but then again they were all +P version throats so half the lands are gone to start with.

 

[josip89]

In 300 round in 338???????

At some show I am talking with some Norvegian shooter and he uses 338 lapua with lothar walther barrel and 300 grain pills with N570, long story short he was well over 5000 round and no loss accuray.

So to me that 300 round is very questionable.

 

[Calvin45]

In 300 round in 338???????

At some show I am talking with some Norvegian shooter and he uses 338 lapua with lothar walther barrel and 300 grain pills with N570, long story short he was well over 5000 round and no loss accuray.

So to me that 300 round is very questionable.

Not questionable at all to me…that the throat shows signs of erosion and flame cracking that is.

One of several reasons why my plan is to just not mess with borescopes…ignorance is bliss and im sure some of my rifles have "toast throats" but the groups they shoot haven't got the memo that the barrel is done for haha

 

[284ackley]

I want to start a thread to discuss throat erosion as it relates to velocity. There has always been the thinking that the higher the velocity of a gun the faster the barrel will wear out. I think this thought comes from comparing slower cartridges to faster cartridges. Like comparing a 300 rum to a 308 win. Obviously one is faster than the other and the faster of the two has much less barrel life. I want to discuss barrel life of the same cartridge loaded at high or low velocity.

The way I see barrel life and how a barrel wears out, is a function of heat and pressure. Cartridges that are more over bore well wear out barrels faster. It is relative to the amount of powder burnt compared to the relative size of the bore. So a 22-250 runs less powder than a 30-06 and burns out a barrel faster. Not because of the amount of powder burnt but because the relative amount of powder to bore size is much higher for the 22-250. So this validates the thinking that overbore cartridges will have less barrel life. The higher concentration of powder burning in a smaller area of throat creates more heat per square inch of bore surface. This all makes sense and is proven out.

What I want to discuss is weather or not increased velocity in the same cartridge changes barrel life. Since I mentioned the 308 win, let's use it for comparison. Let's use a generic bullet for now.

If we load the 308win with a 215g bullet at a velocity of 2450 fps and a pressure of 61,300 psi and compare it to loading a 110g bullet at a velocity of 3450 fps and a pressure of 61,300. Which one burns out the barrel faster and why? I have not tested this and likely never will. It would need two identically built rifles shot sxs and carefully monitored throat wear. My contention is there will be very little difference in barrel wear.

It's less about velocity and far more about over-bore cartridges. That's where throat erosion from excessive burn and heat that does the damage. Compare a 280 Rem at 140gr @3000fps with a 28 Nosler and 200grs @3000 fps. The 28 will shoot out the throat sooner.
As to same caliber, overbore or not, obviously the variable is velocity as well as higher heat, So the higher still wins

 

[Northkill]

Over the years borescoping guns I think there are a couple different types of wear, you'll the blow torch effect that will start at any edge and they fire crack stuff and you'll see just wear I think from the powder.
Where the cone point is coming of the shoulder does change thing BUT it's not like doubling your life or something extreme but if you can keep the cone point on hotter chambering in the neck it does seem to take something from the throat.
Unburnt powder gets blasted out of the case and we know that if you focus anything at speed even water it will cut or abrade and I think it does contribute, I've scoped a number of barrels that were ran with N570 and they were toast in a well maintained rifle in 300 rounds for a 338 but then again they were all +P version throats so half the lands are gone to start with.

I think accuracy life is definitely reduced with the +p throat.

 

[Radman]

H

Great discussion!
Since the barrel erosion is in the throat instead of the muzzle and we assume that most of the powder is burned by the time the bullet gets to the muzzle and is where the bullet is going the fastest then we can assume that powder burn instead of speed is the cause of throat erosion.
There is a lot of energy transfer in a very short time span and space. I see evidence of direct impingement of fire and heat in burned out throats. I do not see evidence of powder erosion by friction in the throat and I do not buy the theory that the powder is wearing the barrel by abrasion. The powder is not a abrasive and most is coated with a lubricant such as graphite. A barrel gets hottest at the chamber end where the bullet is going it slowest not at the muzzle where the bullet is going its fastest. Which leads me to the conclusion that heat from powder burn and not heat from friction is the cause of burned out throats.
So to answer the question I think the type of powder and how it impinges on the throat impacts throat erosion more than bullet weight.

Have to agree with you. I think that this supports your thinking: Most of my favorite calibers are so-called "barrel burners" & what's interesting is the fact that there is RARELY ANY soot, burned powder, un-burned powder or anything visible in the barrel after shooting a box of shells. Sure there is a little copper that scrubs out later but to the naked eye the bores are as clean as a whistle. JMO

 

[TX Badger]

Here is my question. If you look at these two different chamberings both loaded with the same bullet and H 4831 SC which will burn the throat faster? The 7 Rem Mag with 61 grains pushing the bullet at 2959 or the 280 pushing the same bullet at 2888 with 56 grains of powder? There is a big difference in powder charge and velocity. But theoretically the 280 is running at Peak pressure and the 7 rem mag is running a very mild load.

 

[CA48]

In 300 round in 338???????

At some show I am talking with some Norvegian shooter and he uses 338 lapua with lothar walther barrel and 300 grain pills with N570, long story short he was well over 5000 round and no loss accuray.

So to me that 300 round is very questionable.

I saw that guy post he had over 5000 rounds in his 338 lapua with N570. How does his gun shoot? I guess anything is possible but Hard to believe some one has put that many rounds through a barrel with a hot burning powder like 570 and has "no loss in accuracy" Shawn of defensive edge probably has more experience than most running 338 edges with h-1000 and he will tell you to expect around 1200-2000 rounds from an edge Bbl depending on your load, powder used, and individual Bbl.

 

[Welderboy11972]

To me, there's more factors that go into determining barrel throat erosion. Barrel material and barrel shank dimensions are hardly ever talked about. Let's not forget that the barrel also acts as a heat sink. So how well the barrel can shed heat will play a factor in throat erosion to. That was something that I thought about when I built my first custom rifle. 300rum are known to be throat burners. I added alittle extra to the barrel shank when I ordered my stainless barrel. That rifle was my learning rifle. It now has over 2600 rounds through it and it does show some fire cracking for about the first 3 to 4 inches. All the lands are still there and my jump hasn't changed. I shoot 210s vlds with retumbo. And they are moving at a pretty good speed. With that being said. To me barrel material and shank dimension just as much to do with this as being an overbore cartridge. I don't have alot of experience with other different cartridges. So I'm just giving my experience on what I have seen.

 

[wolffo]

as said above
I have read its powder charge to bore diameter as major factor
an example is the 22-243 middlestead
lots of powder small bullet

 

[Mike Matteson]

From what I have been reading. That barrel erosion of 0.004 to 0.007 per 100 rounds. This in match type precision rifle competitions. They talk about increasing powder or increasing or moving the bullet forward. Now I have a rifle just completed (6mm/280AI) with only a couple of round put through it. The barrel is Bartlein Metal grade 400MODBB Heavy in 30" @ 7-1 twist rate. I continue to read about burnout with barrels. So that's why I got a long barrel. So I can have it cut back at both ends as needed. Bartlein said that the barrel should go twice as long as a normal barrel would. We'll see. I also got a 2nd barrel at the same time, but have done anything with it. Some say that that barrel will burn out in 500 round or less. I don't think so, but I been proven wrong before. What the velocity is going to be I don't have clue yet. I am thinking that my go to bullets are going to be Hammer Hunter 100gr. I have others in different weight, mostly heaver to 115gr. My go to powder is generally H4350, and H4831. I have both on hand. Still don't have H1000 or Varget yet. The cleaning will be done by Bartlein standards. So I will watching and will keep you posted. So I will have records from the get go. I just have to get back to Montana to load and shot the rifle. I don't have a bore scope yet but will have one here shortly, and before I start. I will take picture as it is to start with and as develop loads for it.

 

[arch408]

I kinda agree with Calvin45 about borescopes. Sometimes I wish i never had one. Sometimes ignorance is bliss. If the rifle is getting acceptable accuracy, leave it alone. I have a 6.5 Rem Mag that I bought used about 1978, so I don't know the it's history. I used it many years deer hunting. It wasn't a 1/2" rifle, but I managed to kill 3 deer with it at 350 to 400 yards. My closest was about 10 yards. I caught a lot of flack from most hunters because they thought that it was too "small". It never failed me, and every deer I killed only took one shot. It is still an accurate rifle. A few years ago, I bought a bore scope and checked it out. The bore is eroded and has fire cracks in the first inch and a half or so. It also has a land that has copper fouling for several inches. But any way, I think that throat erosion is strictly due to heat. Friction cannot be a big issue because the bullet is traveling way faster at the muzzle and it has no erosion. Every time you fire the rifle, you have a blow torch in the first part barrel under tremendous pressure. The temperature is much higher then the melting point of steel, but it doesn't last long enough to do much damage. If you don't let your barrel cool down between shots, the barrel will erode faster because the steel is closer to it's melting temp. Larger cases have more powder, there fore they have more fuel and more time to heat up the barrel. Also Boyles Law (P1/T1=P2/T2) dictates that anytime you change the temperature or pressure of a gas, you get a coresponding change. IE, when the breech pressure builds to peak, you get a tremendous increase in heat and heat melts or burns up steel.

 

[Buckys]

This falls in with my thinking exactly. I get asked often by customers if they are going to wear their barrel out by using a lighter faster bullet. The short answer is no. If you go to a bigger cartridge to run the same bullet faster, then yes. The barrel wear has little to do with projectile velocity.

Lots of potential factors, but the hotter metal gets, the more vulnerable it is to everything else.

So if I observed one combination wore out very fast and another did not, I would want to continuously monitor the temperature at the most likely point(s) of failure. Not sure where one might buy a ballistic thermocouple, though.

https://www.sto.nato.int/publications/STO%20Meeting%20Proceedings/RTO-MP-AVT-109/MP-AVT-109-15.pdf

 

[Chas1]

I'm not smart enough to make sense of all this but if we're mostly wondering if velocity is a major contributing factor then consider the 223. It can get a 55 grain bullet going 3000 fps yet the barrel life is rather long. The 223 would be a good example of the lower powder charge, relative to bore diameter, improving barrel life.

makes sense to me.