Barrel Life ????

[Boomer]

Eagle, nothing erroneous here. I agree that the gasses and friction of the particles also contribute to the wear, but but you are not quite correct about the rifling wear not a result of the bullet, and the rifling being worn down the barrel.

Examine old barrels and you will see an almost smooth bore near the chamber in addition to the rifling being worn as well.

That is due to friction. Have you ever slugged a barrel? Note how it takes a tremendous amount of force to get the thing started, but once that happens, the slug moves with less effort the further down the barrel you push it. The initial resistance is the massive amount of friction encountered when the bullet first encounters the rifling and the rifling "cuts into" the bullet jacket. The more the bullet moves down the barrel, just as the slug, the lessor degree of friction is encountered and hence, less wear.

Think of it this way;

One pas of the knife on a sharpening steel does not sharpen the blade, it is several passes. It is the abrasion (friction) of the sharpening steel to the knife, which removes metal to sharpen the blade. That's why cast bullets do not impact barrel life nowhere near the same degree as copper jacketed bullets. In physics...they call that "friction".

Cast bullets are fired at far less pressure with lighter powder charges then jacketed bullets typically are, thus the effects of the propellant gases on the barrel steel are minimal. Since the advent of smokeless powder, jacketed bullets and high pressure loadings, barrel steel has improved by necessity. You would be a long time wearing out a modern high quality .22 rimfire barrel, provided the wear wasn't from a cleaning rod, because the powder charge is so much smaller than in a .22-250, yet the friction created by the passage of the bullet in each case is similar as they are dimensionally alike. While it might be true that the passage of jacketed bullets would eventually wear down rifling, the throat of the rifle would be finished long before the wear to the rifling impacted the accuracy potential of that rifle. As for the comparison of a knife and sharpening stone, the sharpening stone is abrasive where as both a jacketed bullet and a rifle barrel are smooth and have a very low coefficient of friction. A better example would be attempting to sharpen that knife on a piece of wet glass.

 

[AlexF]

"Conventional Wisdom" By Josh Benin

Some very interesting reading "Conventional Wisdom" By Josh Benin.

In short, barrel wear is a chemical process not a mechanical one.
http://www.longrangehunting.com/articles/conventional-wisdom-3.php

I didn’t really question the conventional wisdom here for decades, probably because I didn’t have any alternate explanations. Eventually though, I was employed by DuPont, then the manufacturer of IMR smokeless powders. I had nothing to do with powders, but I did ask some of the people who did about barrel erosion and uniformly the response was laughter at the “grit blasting” explanation. Reality, now supported by published studies (and much simplified) goes like this. Powder begins to burn. Pressure rises and temperatures in the burning gas are very high, thousands of degrees, and the gas is actually a plasma, ions rather than molecules and very reactive. The atmosphere is high in hydrogen, carbon and nitrogen. Under these conditions, minute amounts of the gas plasma react with the adjacent steel, forming new compounds with mechanical properties differing from the steel, generally being harder and less ductile. This happens on a very small scale, only molecules thick, but on subsequent firings the harder compounds cannot expand with the underlying steel, and minute bits flake off, giving rise to a cracked and eroded surface. This effect is greatest in the barrel throat, where both temperatures and pressures are greatest. In short, barrel erosion isn’t a result of mechanical blasting. It’s mostly chemistry.

 

[paperslayer]

The 204 because of the speed of the bullet will eat the rifling at a much higher rate, but i suspect 1-2000 rounds would be normal.

223 because of its slower muzzle velocity is probably good for 6-10,0000

Has nothing to do with speed of the bullet.

Here is a far better tool for estimation. Having said that I have had several 204's as I am an avid varminiter. I have worn out a barrel in a weekend.

"the case capacity in grains of water divided by the area (in square inches) of the bore cross-section. This gives us an Index which lets us compare various cartridge designs."

As a comparison, the 6.5-284 is a cartridge notorious for 1000 rounds or less of match accuracy.

The 308 is good for 4-5000 of match accuracy (often more, but there are many variables.

the 7 WSM is good for 700 rounds of match accuracy.

 

[sobo4303]

Some very interesting reading "Conventional Wisdom" By Josh Benin.

In short, barrel wear is a chemical process not a mechanical one.
http://www.longrangehunting.com/articles/conventional-wisdom-3.php

Alex F,

Thank you for that article reference. In my earlier post, I was somewhat chastised for my reference to friction. What I stated was that barrel wear was the result of friction and heat.

I have commisioned studies on the negative effects of high temperatures on hardened steel (plasma/gasification of solid wastes) and the impacts on operations infrastructure and completely agree with how heat impacts the throat area in a firearm. I also have seen firsthand the effects of heat and friction (automotives) in other applications and how friction is used as an aid to generating heat in fluid pressure systems and also as a source of incredible wear on piping systems.

I think most are saying the same thing overall in answering the OP's question, just in different ways.

 

[Eagleye]

I agree that the "blasting" effect of particles in minimal compared to the erosive effect of the high temperature powder combustion.
However minimal it may be, the combination of factors contributes to the erosion of the throat area of the barrel.
I would guess [probably a poor word choice] that 95% of the erosion is the result of the hot gases and the chemistry that takes place during the "firing" event.
Eagleye.