High Velocity Throat Erosion

[VenatusDominus]

I would hypothesize that a 6.5 PRC shooting a 130 gr at 2849 ft/sec with 50.9 grs of Accurate 4350 (moderate load aprox 59,850 psi) will shoot out a barrel faster than a 6.5 Creedmoor shooting the same 130 gr at the same 2849 ft/sec with 44.9 grs of Accurate 4350 (max load 60,600 psi). Assuming all other variables are the same ( barrel length and contour, ambient temperature, altitude and firing intervals)

I pulled the load data from the Hodgdon web site. The data for the CM is their published max, The data for the PRC was extrapolated from their published data assuming a linear relationship between load, velocity and pressure. I do realize that the relationship is not linear, but it made the math simple and is close enough for my hypothesis. Someone with QuickLOAD may be able to get more precise load and pressure values for the PRC 130 gr at 2849 ft/sec. I used the data for Accurate 4350 because it was the only powder that was common between the two rounds for the same weight bullet.

 

[RidgeTop]

I think the answer is yes. The throat is the portion of the bore that receives the highest duration of high temps and pressures. The throat gets toasted first because of those high temps/pressures.

The heavier the bullet, the longer the duration of the high heat and temperatures at the throat. The heavier bullet remains near the chamber/throat slightly longer than a lighter bullet, because it takes a longer period of time to get that heavier bullet accelerated away from the chamber/throat. And I think that's what the OP was asking about.

For what that's worth... I should note my comments are primarily based on theory, much more so than personal experiences and bore scoping after the fact. And this theory doesn't include any consideration of different powder burning temperatures. A powder that generates a higher throat temperature is certain to heat crack the throat faster than a powder generating a lower throat temperature.

You did not read my BTW in my post #58 above.

 

[baldhunter]

Barrel Life Calculator

Barrel Life Calculator

pierrevanderwalt.com

 

[Mike Matteson]

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.

Nothing wrong with a 6.5 Rem Mag for deer. I mostly used a 25/06 for years, and mostly one shot kills from 30yds to 500+yds. Now I step up to hunting elk, and I increase my rifle to 308 NMag. I wouldn't say my 25/06 is a good elk rifle, but there people that use them.
One thing for sure this has created a lot of interest in just a few days.

 

[ButterBean]

Barrels are the cheapest part of what we are all doing, I for say just let her eat

 

[milo-2]

Narrate the cheapest part of what we are all doing, I for say just let her eat

I'm assuming you just said barrel life is not a concern to you, if so we're on the same side. Lately with component shortages, I chamber rifles for the components on hand. Even if I had my pick of goodies, doubt I'd change bullets or powder to get 200 more rds from a barrel.
Nor would I alter my shooting habits, if the person I'm with wants to shoot 20 strings, who am I to argue with that logic. I used to think when I shot alone I exercised more restraint, not true, I'm a bigger idiot when unchecked, lol. We have steel to 2100 yards, get on a roll, barrels get hot. The trigger finger ruins more barrels than anything one is pouring into them.

 

[orkan]

People could literally buy the best of everything in this discipline, and it wouldn't equal the cost of 1 nice boat.

Nothing is expensive. Certainly not barrels.


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[xsn10s]

I wouldn't call barrel swapping the cheapest part of what we do. But if a person chooses a cartridge with certain characteristics then that's their choice. Anything has pros and cons. Everything is a trade off.

 

[Quintus]

To expand a little on Orkins video. I agree with the theory on pressure. There is the shear outward pressure of gas and bullet, but you also have to add the pressure of thermal expansion as the barrel steel is also growing as it heats creating pressure in a different or all directions. All of these may also make the steel susceptible to some degree of chemical reaction possibly causing erosion through reaction as opposed to abrasion? Just spitballin.

 

[Lenny Foffa]

Excellent thread!! Thanks for opening up this dialog. This is an important topic!! As I shoot a .270 Win, and also .270 Weatherby Mag, Purchased new in 1979, I cannot help but wonder if 800 to 1000 rounds have caused damage, in that older barrel. I wonder if I can expect to get 2500 Rounds of a fairly hot, but not max loads using 130 and 150 grain bullets. This is not based on science, I used to just think that as the groups sized open up, I / you would know that end is near. When the groups become 2.5 to 3 MOA , unacceptable for hunting , it is then time for a new barrel. Looking forward to others responses.

 

[Heym500]

tag

 

[Philward]

Maybe:

• barrels need better metallurgy, create a steel that will not firecheck etc.
• propel projectiles with something other than a burning propellant to see if the same barrel wear result. (not sure how to create 60k psi)

 

[josip89]

First LW steel is different than the typical barrel steel used so right out of the gate there is a bonus. Then define no accuracy loss, that can vary from I hit it to it's opened up an inch at 1000+, very subjective. I've seen barrels shoot out standing with inches of rifling toasted out of it, my 308 is a smoothbore for nearly an inch and then tapers in some rifling and it'll shoot very decent groups well under 6 inches at 1000. So there can be a lot of variables there, playing with the throats will lead to shorter life if it gets temperamental due to wear and an aggressive case design.

Look I do not personaly that man.I know somwhere on the web there is article about them and his rifle.
I know Lothar Walther barrel is better than typical American made.
I dont know what is "no accuracy loss" for that man.

But on the other hand ,I myself have SSG08 in 338 Lapua and I myself shoot over 2500 various round ,but last 1000 round was 300 berger with velocity 2919 fps and group was one ragged hole ,of course powder was N570.

So when someone say with 300 round in 338 (whatever 338) barrel is toast, there must be some other reason than N570.
I dont know what barrel quality is that?


I saw on the lot places that people say that N570 is very hard and dirty on the barrels and maybe it is hard (dirty is for sure),but on the other hand You can not get these velocity with any other powder.

On the lot places they compare H1000 and N570 and I personaly dont know what to compare.
If You want less velocity , cleaner barrel and few round more You can use H1K.

 

[josip89]

Maybe:

• barrels need better metallurgy, create a steel that will not firecheck etc.
• propel projectiles with something other than a burning propellant to see if the same barrel wear result. (not sure how to create 60k psi)

Definitely true.
Many people want more quality barrels and more quality powders.
I would also like to see some bigger imprvment in these areas.