High Velocity Throat Erosion

[Philward]

I believe it is north of 3000 degrees - only instantaneous.

Looked it up, 5000°F, depending on powder. That temp would be isolated on the inner surface of the barrel and only for a fraction of second, rest of barrel as heat sink and as strength to contain blast.

 

[Fiftydriver]

So what is the temperature of combustion in a chamber at 60k psi?

not sure but different powders will have different temperatures at that pressure level. I did read somewhere that some figured the actual time that a barrel withstood working temps while being fired in its useful life and it was around 2 minutes. Meaning if you took the time it took for a bullet to travel down the bore for each shot and added all that time up over the life of the barrel, it equalled 2 minutes. Now i may not be remembering the exact number correctly but it was a very short time frame!!

 

[eoperator]

That barrel life calculator in post #87 lists the heat potential of most powders, interesting resource if it is correct.

 

[coyotemaster]

I think one of the biggest factors in any of this is the powder used. Higher energy powders like RL17, RL26, N570, and others known to get top velocity in certain cartridges also tend to be harder on barrels. My non scientific and very possibly incorrect hypothesis is due to maintaining peak pressure for a longer period of time, thus creating more heat in the barrel leading to shorter barrel life. I don't think bullet speed makes much of a difference in a particular cartridge, it think powder choice is the biggest factor. For instance, using H1000 vs N570 in a 300 rum, I would bet my lunch money the H1000 would give longer barrel life. I would think if your shooting a 165 grain bullet going faster or 245 grain bullet going slower, likely wouldn't make a measurable difference.

My experience with the Swift, a supposedly notorious barrel burner, falls inline with your supposition. IMR 4064 is the gold standard with 50-52 grain bullets but it will ruin a throat in short order if shot fast and hard without consideration for barrel temp. I have not shot AA 2700 in a Swift but it is reported to significantly lengthen barrel life, and it obviously is a much slower powder.

That said, Jim Carmichael wrote in THE BOOK OF THE RIFLE that he had a Swift with over 5K rounds through it that was still "nicely" accurate and I think he was fond of IMR powders. Jim was fond of velocity penning the line. If you've got a race horse you ought to let it run!

The heavier longer bullet theory has merit as well. I built a fast twist Swift and with the 9T shooting 68 gr. bullets and though they are incredible,compared to 50s in the wind, they do not supposedly enjoy a long barrel life.

I do believe the nut behind the gun has a huge impact on barrel life, keep it cool, keep it clean and modern barrel steel is pretty resilient.

 

[Fiftydriver]

My experience with the Swift, a supposedly notorious barrel burner, falls inline with your supposition. IMR 4064 is the gold standard with 50-52 grain bullets but it will ruin a throat in short order if shot fast and hard without consideration for barrel temp. I have not shot AA 2700 in a Swift but it is reported to significantly lengthen barrel life, and it obviously is a much slower powder.

That said, Jim Carmichael wrote in THE BOOK OF THE RIFLE that he had a Swift with over 5K rounds through it that was still "nicely" accurate and I think he was fond of IMR powders. Jim was fond of velocity penning the line. If you've got a race horse you ought to let it run!

The heavier longer bullet theory has merit as well. I built a fast twist Swift and with the 9T shooting 68 gr. bullets and though they are incredible,compared to 50s in the wind, they do not supposedly enjoy a long barrel life.

I do believe the nut behind the gun has a huge impact on barrel life, keep it cool, keep it clean and modern barrel steel is pretty resilient.

For what its worth, i have had two chamberings come into the shop more often then any with supposed shot out barrels, the 220 swift and the 257 wby. Early 75% of the time, after removing a couple pennies worth of copper out of the bores, they shoot great again. Often cleaning practices leave alot to be desired and people get behind on cleaning and can be a challenge to get cleaned completely.

the swift got a rep for a barrel burner back early in its career when barrel steel was really not good for erosion and understanding barrel life was not that great. Today with our top quality stainless barrels, it has roughly the same barrel life as the 22-250.

 

[nralifer]

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.

You pose an interesting question that I have commented on before. Maybe you have some data, but all should realize that the 308 Win is one of the most efficient cartridges out there. It has a very long throat life. The only conclusive way to answer the question is to actually test 2 different bullets each being shot from new barrels that have identical twists, bore diameters and length. Pressure should be monitored in each barrel with piezoelectric sensors and both loads should use identical components (powder, primers, brass) and be prepared to shoot a minimum of about at least 1000 shots from each barrel. That means 1000 bullets of each weight. The erosion of the throat will start with fire cracking at the lead and first portion of the rifling. Tho get any sort of reliable conclusion in any experiment only one variable needs to be controlled. All other potential variables meed to be controlled.

 

[RockyMtnMT]

You pose an interesting question that I have commented on before. Maybe you have some data, but all should realize that the 308 Win is one of the most efficient cartridges out there. It has a very long throat life. The only conclusive way to answer the question is to actually test 2 different bullets each being shot from new barrels that have identical twists, bore diameters and length. Pressure should be monitored in each barrel with piezoelectric sensors and both loads should use identical components (powder, primers, brass) and be prepared to shoot a minimum of about at least 1000 shots from each barrel. That means 1000 bullets of each weight. The erosion of the throat will start with fire cracking at the lead and first portion of the rifling. Tho get any sort of reliable conclusion in any experiment only one variable needs to be controlled. All other potential variables meed to be controlled.

How would you have identical components if one rifle is shooting heavy for caliber bullets at low vel and one rifle shooting light for caliber bullets at high vel? You say a lot of cool stuff, but the point of the thread was to talk about one of the wives tales that is spun around campfires and then quoted as fact. I started the thread in response to a comment that you made to @ButterBean about him running a Hammer Bullet at 4000 fps. Your comment was something along the line of "Why would you do that, it will just wear your barrel out faster.".

I understand that it not easy to prove, because there is so many variables, but saying that speed will burn out a barrel faster is also just as hard to prove. You should not have made the statement as if it were fact.

I still stand on my theory that identical rifles run at the same pressure with greatly diff vel will show no diff in barrel wear.

 

[Mike Matteson]

For what its worth, i have had two chamberings come into the shop more often then any with supposed shot out barrels, the 220 swift and the 257 wby. Early 75% of the time, after removing a couple pennies worth of copper out of the bores, they shoot great again. Often cleaning practices leave alot to be desired and people get behind on cleaning and can be a challenge to get cleaned completely.

the swift got a rep for a barrel burner back early in its career when barrel steel was really not good for erosion and understanding barrel life was not that great. Today with our top quality stainless barrels, it has roughly the same barrel life as the 22-250.

They also claim the 22-250 is faster than the 220 swift. That was one of the reason they came with the 22-250 because it was slower and didn't burn barrels. I have a 6mm/280AI that should push bullet down the tube very quickly. It's had 2 round down the tube so far. I had the reamer built for it. I also got a 32" barrel Bartlein P Heavy steel is there 400MODBB grade. Cut back to 30" to start with. Figuring on it being a barrel burner. I even went as far as getting a 2nd barrel for it. I didn't have it chamber, just sitting there. I am headed back to Montana here in September. I will get into reloading that rifle at that time. To me it will fun to see what happens.

 

[Calvin45]

Stainless steel is softer than chrome moly steel. Chrome moly steel will last longer than stainless steel when used in barrels. Stainless steel is softer and easier to tool, making it easier to produce an accurate barrel than the harder chrome moly. Chrome lined barrels are even less prone to wear but it is difficult to get a perfectly consistent lining and so can have a negative effect on accuracy.

Really? I had always figured stainless would be tougher. But that was indeed just assumption. Off to do my research…thanks

 

[Mike Matteson]

For what its worth, i have had two chamberings come into the shop more often then any with supposed shot out barrels, the 220 swift and the 257 wby. Early 75% of the time, after removing a couple pennies worth of copper out of the bores, they shoot great again. Often cleaning practices leave alot to be desired and people get behind on cleaning and can be a challenge to get cleaned completely.

the swift got a rep for a barrel burner back early in its career when barrel steel was really not good for erosion and understanding barrel life was not that great. Today with our top quality stainless barrels, it has roughly the same barrel life as the 22-250.

They were also using lower grain bullets in the swift too. Pushing down the tube over 4000fps. I got a 220 swift before the 22/250 came out. The other is I use IMR4064 powder in it. Now I haven't used it much in several years, due to lack of places to shot ground squirrel at. I have found areas with P. dogs are at. So I am going to turn my attention to that. I also have a young grandson that getting of age. So I am going to take him along, and get him set to doing some P dog hunt or shooting. His dad has him using centerfire rifles for a year or too now.

 

[Calvin45]

For what its worth, i have had two chamberings come into the shop more often then any with supposed shot out barrels, the 220 swift and the 257 wby. Early 75% of the time, after removing a couple pennies worth of copper out of the bores, they shoot great again. Often cleaning practices leave alot to be desired and people get behind on cleaning and can be a challenge to get cleaned completely.

the swift got a rep for a barrel burner back early in its career when barrel steel was really not good for erosion and understanding barrel life was not that great. Today with our top quality stainless barrels, it has roughly the same barrel life as the 22-250.

I recall the gun writers pre-determined that the .264 win mag was a barrel burner too. Killed it before it was born in a way. And now we have such clamour surrounding the 6.5-300 wby and 26 Nosler haha. Both of which only beat the win mag by MAYBE 200 fps out of the barrel lengths of the rifles they're sold in and burn a boat load more powder to get there

 

[Mike Matteson]

It's my understanding the wby mag have a fair amount of free bore in them to start with. That was one of the ways to achieve greater velocity with there rifles. Maybe I am wrong, but that was my understanding.

 

[Calvin45]

It's my understanding the wby mag have a fair amount of free bore in them to start with. That was one of the ways to achieve greater velocity with there rifles. Maybe I am wrong, but that was my understanding.

No that's correct…not a bad thing either! Compare yhe 7mm rem mag to yhe 7mm weatherby…the difference in velocity both in factory ammo and published data has little to do with any minute case capacity difference (and while it looks cool I am skeptical of that curvy shoulder actually changing anything).

Lots of freebore for the wby And a ridiculously anemic saami rating for yhe rem and it's a done deal. One generates true magnum performance. The other is an overpriced 270 haha (I may be exaggerating a tad…)

 

[Mike Matteson]

One thing about Weatherby is they build a petty rifle. We are going to have the Weatherby boy's on our tails.