What factor causes the most barrel wear?

Redhook · May 12, 2002, 02:55 AM

I realize that most rifles chambered for magnum cartridges usually have a bbl life half that of most standard cartridges. But what is the exact cause of this?

You can load a .300win mag down to speeds of a .308win (2650fps) using a heavier bullet, and from what I've been told, the barrel will still wear faster. So, I would have to guess that it is either the heavier bullet weight or the higher quantity of powder in the cartridge. Does anyone know?

-Red-

blades67 · May 12, 2002, 06:18 AM

Bullet and powder velocity and poor cleaning habits. In that order.

**Bud Helms** · May 12, 2002, 07:54 AM

Never heard about "magnums" having half the barrel life of "standard" chamberings before.

One thing that will eventually occur in a really large case capacity bottle-neck cartridge with really slow burning powders is throat/leade erosion. That could progress into the rifling, but it'd take a while for it to show up. 'Might not even notice it if you don't shoot for group once in a while. I had a .25-'06 that grouped outstanding except for a flyer (and I mean a 2 incher at 100 yds!) about every 3 or 4 rounds. Cerrosafed the chamber and there it was! 'Looked like somebody had torched one side of the throat. Ugly. The only way to even minimize it was to partial resize and index the rounds when chambering.

That's what you can end up with, potentially, with your .300 Win Mags, your 7 mm Mags, this caliber "Mag", that caliber "Mag".

'Might seem a tad off-topic, but ... I'm looking in an old Speer manual (No. 11) and see a .30-'06 load, with 4350 and a 168 gr boattail match bullet, at 59.0 grs (max) for 2978 fps MV out of a 24 inch barrel. No other details.

A .300 Win Mag, same bullet, same powder, 4350, at a 74.0 gr (max) charge at 3215 fps MV. No details.

That is a 25% increase in the powder charge for an 8% increase in velocity. A lot of variables here ... brand of rifle, conditions at time of firing, etc..

There's a bunch of different ways to compare any two chamberings. The .300 Win Mag will send a 180 gr bullet out faster than a .30-'06 will send a 150 ... it shoots flatter ... but I'm just talking about barrel life and the effect of powder charge, as it affects barrel life.

Each one of those little powder pellets (ball or rod) is a little sparkler trying to get out of the case first. As they pass the mouth of the case, if they haven't completely burned yet, they take a toll on the surrounding material ... the case mouth, the throat, the leade and eventually the rifling. As the pressure builds and the heat pulse occurs, it makes these areas more vulnerable to the erosion. It takes a while. The more "over bore" the chambering is, the faster it happens.

You mileage, of course, may vary ...

444 · May 12, 2002, 11:58 AM

What factor causes the most barrel wear?

Heat

C.R.Sam · May 12, 2002, 01:44 PM

Sensop nailed it.
444 condensed it.

Ultimate in barrel erosion was my 22-06 toy of long ago. Lost the barrel before we got a load worked up.

Sam

Gewehr98 · May 12, 2002, 02:02 PM

Overbore is a condition where:

You have lots of "boiler room", meaning case capacity, to fill up with powder, in the effort to get more velocity for a given bullet/ bore diameter. But you get into a zone of diminishing returns for the additional "boiler room" capacity.

There's an efficiency curve, where each grain of additional powder gives a corresponding increase in muzzle velocity for the selected bullet.

"Efficient" rounds maintain that curve, then they just plain run out of case capacity for any more powder for additional velocity.

Here's an example: The 7mm-08 is considered to be an "efficient" round, by virtue of it's ideal case volume and bore ratio. It gets good velocity for the amount of powder burned.

The 7mm STW is considered to be an "overbore" round, using the same yardstick. Sure, it can squirt out a 7mm bullet at velocities unheard of from the 7mm-08, but it does so at a cost or two. Namely, LOTS more powder burned, and rapid barrel wear as compared to more efficient cartridges.

The above examples are two extremes of the scale. P.O. Ackley was really big on case efficiency, and had a rather elegant way of describing when one was entering the realm of "overbore". If adding more powder behind a given bullet didn't produce a proportional rise in velocity, you had gone from efficient to overbore.

Look at the 7mm Remington Magnum, and then the 7mm STW. The 7mm STW has more case capacity for powder, and it does indeed produce more velocity than the 7mm Remington Magnum. But the velocity increase isn't proportional to the extra grains of powder used to get that increase.

Where overbore really starts to manifest itself is in barrel wear. An old gunsmith explained barrel life to me in terms even I could understand:

Barrel life is a function of how many pounds of powder you send through it, period.

Think about that one. A cartridge of a given caliber that tools along using an efficient round, say a 7mm-08, with only 40 grains of a given powder, will outlast another 7mm barrel, this time chambered in an overbore 7mm STW, that will use over 80 grains of powder to zip a 7mm bullet on it's way. Either way, the barrel is only going to last for X number of pounds of powder. How you "dispense" those pounds of powder through the bore is what determines barrel life. Here's the math, a pound of powder is 7000 grains. Divide that 7000 grains by 40 grains to see how many rounds of 7mm-08 you will shoot per pound of powder. Now take that same 7000 grains of powder, divide by 80 grains for the 7mm STW, and you'll notice that you get fewer rounds per pound of powder, and each round definitely sends more powder down the barrel than it's more efficient 7mm-08 cousin. Rephrased - Over the life of a given barrel, you'll end up sending more pounds of powder down an overbore caliber barrel than you will one that's an efficient caliber if you plan on shooting the same number of rounds.

You can have a barrel in 6.5x55 Swedish Mauser outlive the owner, but a .264 Winchester Magnum may not last you more than 2000 rounds.

__________________
"Bother", said Pooh, as he chambered another round...

**Mike Irwin** · May 12, 2002, 02:13 PM

What really causes the most barrel wear?

Generally, improper cleaning methods, such as letting the cleaning rod drag against the muzzle of the gun, which can rather quickly cause a sharp drop in accuracy.

444 · May 12, 2002, 02:28 PM

"Barrel life is a function of how many pounds of powder you send through it, period. "

Let's say we take two brand new rifles chambered for .223 Remington. As we fire them, we measure the wear on the barrel to determine useful barrel life, or possibly a minimum acceptable degradation in accuracy. Out of each rifle we fire 1000 rounds and do an evaluation. In rifle A, we fire three shot groups, allowing the rifle to cool for 10 minutes between three shot groups. In rifle B, we fire 30 round mags on full-auto. One mag after the other until 1000 rounds were fired. Do you think they would both exhibit the same degree of wear at the end of 1000 rounds ?
I have never done such a test, so I don't really know. But, if I had to hazard a guess, I would guess that the extreme heat generated by the full auto fire would have a great effect on the equation.

Gewehr98 · May 12, 2002, 02:44 PM

All other factors being equal, I'd definitely agree that full-auto or even rapid-fire contributes a lot to barrel erosion. I like how the German MG-42 fixed that problem with the quick-change barrel. A few enterprising benchresters have come up with quick-change barrels for their match rigs, too. I can only imagine the money tied up in one of those rigs with a handful of spare pre-chambered Krieger, Obermeyer, Shilen, or BlackStar barrels ready to go.

But I'll still stick by my guns (no pun intended) and say that a 7mm Remington magnum will wear out it's throat a good bit sooner than a 7mm-08 - based solely on the overbore equation.

And my 6.5mm-.300 Weatherby Magnum will chew through a barrel about the same time I work up a good-shooting handload for it. Meanwhile, my 6.5x55 Swede will keep chugging along. Bummer. I would've thought barrel steels would have improved enough to preclude that problem, but those same steels have to be machinable.

Did see a water-cooled varmint rig once, used a Coleman cooler full of ice water to pump through a barrel jacket. Bit of a variation on the Maxim gun, I figured. Car battery, 12v bilge pump, pretty slick. Deadly on the prairie dogs, too.

444 · May 12, 2002, 02:51 PM

I wasn't trying to be smart. I recently tried to buy a HB, Flat Top, AR-15. I said, what kind of groups are you getting out of it ? He said, I don't know, but you ought to see how fast it will empty a 30 round mag.
I said, "Let me get back to you on this".

**Bud Helms** · May 12, 2002, 05:16 PM

Yup. I think 444 speak true too. I also agree with Gewehr98. And, dammit, I think I have to agree with Mike Irwin too.

I hate it when that happens!

C.R.Sam · May 12, 2002, 06:59 PM

444......True indeed. I have been there when .30 barrel became toast in a couple of minutes.

Mike right too. Clean em to death with haphazzard stroking.

Sooooo.......We have intense over capacity loads causing heat and corrosion and erosion in throat/barrel.

Kill em with rapid fire shooting....or full auto without cooling breaks. Again, corrosion/erosion of throat and barrel.

Wear em with cleaning rods, stainless brushes etc.

Any and/or all of the above.

Sam

Archie · May 12, 2002, 10:31 PM

The burn temperature in a high power rifle is around 4000 - 5000 degrees. That's cutting torch temperature.

That's what blows out the leade section, anyway.

Bad cleaning will rot out the rest of the bore.

Bogie · May 13, 2002, 12:30 PM

Bad cleaning, or not enough cleaning.

As you fire rounds, you're also eroding the throat, and pressure/heat scarring the first few inches. As this roughens, the barrel will become erratic.

May 12, 2002, 02:55 AM	#1
Redhook Senior Member Join Date: January 25, 2001 Posts: 254	What factor causes the most barrel wear? I realize that most rifles chambered for magnum cartridges usually have a bbl life half that of most standard cartridges. But what is the exact cause of this? You can load a .300win mag down to speeds of a .308win (2650fps) using a heavier bullet, and from what I've been told, the barrel will still wear faster. So, I would have to guess that it is either the heavier bullet weight or the higher quantity of powder in the cartridge. Does anyone know? -Red-

May 12, 2002, 06:18 AM	#2
blades67 Senior Member Join Date: April 22, 1999 Location: Chandler, Arizona, USA Posts: 6,014	What factor causes the most barrel wear? Bullet and powder velocity and poor cleaning habits. In that order. __________________ Guns cause crime like spoons cause Rosie O'Donnell to be fat! I hunt, therefore I am.

May 12, 2002, 07:54 AM	#3
Bud Helms Senior Member Join Date: December 31, 1999 Location: Middle Georgia, USA Posts: 13,198	Never heard about "magnums" having half the barrel life of "standard" chamberings before. One thing that will eventually occur in a really large case capacity bottle-neck cartridge with really slow burning powders is throat/leade erosion. That could progress into the rifling, but it'd take a while for it to show up. 'Might not even notice it if you don't shoot for group once in a while. I had a .25-'06 that grouped outstanding except for a flyer (and I mean a 2 incher at 100 yds!) about every 3 or 4 rounds. Cerrosafed the chamber and there it was! 'Looked like somebody had torched one side of the throat. Ugly. The only way to even minimize it was to partial resize and index the rounds when chambering. That's what you can end up with, potentially, with your .300 Win Mags, your 7 mm Mags, this caliber "Mag", that caliber "Mag". 'Might seem a tad off-topic, but ... I'm looking in an old Speer manual (No. 11) and see a .30-'06 load, with 4350 and a 168 gr boattail match bullet, at 59.0 grs (max) for 2978 fps MV out of a 24 inch barrel. No other details. A .300 Win Mag, same bullet, same powder, 4350, at a 74.0 gr (max) charge at 3215 fps MV. No details. That is a 25% increase in the powder charge for an 8% increase in velocity. A lot of variables here ... brand of rifle, conditions at time of firing, etc.. There's a bunch of different ways to compare any two chamberings. The .300 Win Mag will send a 180 gr bullet out faster than a .30-'06 will send a 150 ... it shoots flatter ... but I'm just talking about barrel life and the effect of powder charge, as it affects barrel life. Each one of those little powder pellets (ball or rod) is a little sparkler trying to get out of the case first. As they pass the mouth of the case, if they haven't completely burned yet, they take a toll on the surrounding material ... the case mouth, the throat, the leade and eventually the rifling. As the pressure builds and the heat pulse occurs, it makes these areas more vulnerable to the erosion. It takes a while. The more "over bore" the chambering is, the faster it happens. You mileage, of course, may vary ... Last edited by Bud Helms; May 12, 2002 at 08:33 AM.

May 12, 2002, 02:02 PM	#6
Gewehr98 Senior Member Join Date: June 30, 2000 Location: Token Creek, WI Posts: 4,067	From another posting on this very subject... Overbore is a condition where: You have lots of "boiler room", meaning case capacity, to fill up with powder, in the effort to get more velocity for a given bullet/ bore diameter. But you get into a zone of diminishing returns for the additional "boiler room" capacity. There's an efficiency curve, where each grain of additional powder gives a corresponding increase in muzzle velocity for the selected bullet. "Efficient" rounds maintain that curve, then they just plain run out of case capacity for any more powder for additional velocity. Here's an example: The 7mm-08 is considered to be an "efficient" round, by virtue of it's ideal case volume and bore ratio. It gets good velocity for the amount of powder burned. The 7mm STW is considered to be an "overbore" round, using the same yardstick. Sure, it can squirt out a 7mm bullet at velocities unheard of from the 7mm-08, but it does so at a cost or two. Namely, LOTS more powder burned, and rapid barrel wear as compared to more efficient cartridges. The above examples are two extremes of the scale. P.O. Ackley was really big on case efficiency, and had a rather elegant way of describing when one was entering the realm of "overbore". If adding more powder behind a given bullet didn't produce a proportional rise in velocity, you had gone from efficient to overbore. Look at the 7mm Remington Magnum, and then the 7mm STW. The 7mm STW has more case capacity for powder, and it does indeed produce more velocity than the 7mm Remington Magnum. But the velocity increase isn't proportional to the extra grains of powder used to get that increase. Where overbore really starts to manifest itself is in barrel wear. An old gunsmith explained barrel life to me in terms even I could understand: Barrel life is a function of how many pounds of powder you send through it, period. Think about that one. A cartridge of a given caliber that tools along using an efficient round, say a 7mm-08, with only 40 grains of a given powder, will outlast another 7mm barrel, this time chambered in an overbore 7mm STW, that will use over 80 grains of powder to zip a 7mm bullet on it's way. Either way, the barrel is only going to last for X number of pounds of powder. How you "dispense" those pounds of powder through the bore is what determines barrel life. Here's the math, a pound of powder is 7000 grains. Divide that 7000 grains by 40 grains to see how many rounds of 7mm-08 you will shoot per pound of powder. Now take that same 7000 grains of powder, divide by 80 grains for the 7mm STW, and you'll notice that you get fewer rounds per pound of powder, and each round definitely sends more powder down the barrel than it's more efficient 7mm-08 cousin. Rephrased - Over the life of a given barrel, you'll end up sending more pounds of powder down an overbore caliber barrel than you will one that's an efficient caliber if you plan on shooting the same number of rounds. You can have a barrel in 6.5x55 Swedish Mauser outlive the owner, but a .264 Winchester Magnum may not last you more than 2000 rounds. __________________ "Bother", said Pooh, as he chambered another round... __________________ "Bother", said Pooh, as he chambered another round... Neural Misfires

May 12, 2002, 02:13 PM	#7
Mike Irwin Staff Join Date: April 13, 2000 Location: Northern Virginia Posts: 41,380	What really causes the most barrel wear? Generally, improper cleaning methods, such as letting the cleaning rod drag against the muzzle of the gun, which can rather quickly cause a sharp drop in accuracy. __________________ "The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza Baby Jesus cries when the fat redneck doesn't have military-grade firepower.

May 12, 2002, 11:58 AM	#4
444 Senior Member Join Date: November 20, 2000 Location: Ohio Posts: 3,968	What factor causes the most barrel wear? Heat

May 12, 2002, 01:44 PM	#5
C.R.Sam Senior Member Join Date: October 29, 1999 Location: Dewey, AZ Posts: 12,858	Sensop nailed it. 444 condensed it. Ultimate in barrel erosion was my 22-06 toy of long ago. Lost the barrel before we got a load worked up. Sam

May 12, 2002, 02:28 PM	#8
444 Senior Member Join Date: November 20, 2000 Location: Ohio Posts: 3,968	"Barrel life is a function of how many pounds of powder you send through it, period. " Let's say we take two brand new rifles chambered for .223 Remington. As we fire them, we measure the wear on the barrel to determine useful barrel life, or possibly a minimum acceptable degradation in accuracy. Out of each rifle we fire 1000 rounds and do an evaluation. In rifle A, we fire three shot groups, allowing the rifle to cool for 10 minutes between three shot groups. In rifle B, we fire 30 round mags on full-auto. One mag after the other until 1000 rounds were fired. Do you think they would both exhibit the same degree of wear at the end of 1000 rounds ? I have never done such a test, so I don't really know. But, if I had to hazard a guess, I would guess that the extreme heat generated by the full auto fire would have a great effect on the equation.

May 12, 2002, 02:44 PM	#9
Gewehr98 Senior Member Join Date: June 30, 2000 Location: Token Creek, WI Posts: 4,067	444 speak true. All other factors being equal, I'd definitely agree that full-auto or even rapid-fire contributes a lot to barrel erosion. I like how the German MG-42 fixed that problem with the quick-change barrel. A few enterprising benchresters have come up with quick-change barrels for their match rigs, too. I can only imagine the money tied up in one of those rigs with a handful of spare pre-chambered Krieger, Obermeyer, Shilen, or BlackStar barrels ready to go. But I'll still stick by my guns (no pun intended) and say that a 7mm Remington magnum will wear out it's throat a good bit sooner than a 7mm-08 - based solely on the overbore equation. And my 6.5mm-.300 Weatherby Magnum will chew through a barrel about the same time I work up a good-shooting handload for it. Meanwhile, my 6.5x55 Swede will keep chugging along. Bummer. I would've thought barrel steels would have improved enough to preclude that problem, but those same steels have to be machinable. Did see a water-cooled varmint rig once, used a Coleman cooler full of ice water to pump through a barrel jacket. Bit of a variation on the Maxim gun, I figured. Car battery, 12v bilge pump, pretty slick. Deadly on the prairie dogs, too. __________________ "Bother", said Pooh, as he chambered another round... Neural Misfires

May 12, 2002, 02:51 PM	#10
444 Senior Member Join Date: November 20, 2000 Location: Ohio Posts: 3,968	I wasn't trying to be smart. I recently tried to buy a HB, Flat Top, AR-15. I said, what kind of groups are you getting out of it ? He said, I don't know, but you ought to see how fast it will empty a 30 round mag. I said, "Let me get back to you on this".

May 12, 2002, 05:16 PM	#11
Bud Helms Senior Member Join Date: December 31, 1999 Location: Middle Georgia, USA Posts: 13,198	Yup. I think 444 speak true too. I also agree with Gewehr98. And, dammit, I think I have to agree with Mike Irwin too. I hate it when that happens!

May 12, 2002, 06:59 PM	#12
C.R.Sam Senior Member Join Date: October 29, 1999 Location: Dewey, AZ Posts: 12,858	444......True indeed. I have been there when .30 barrel became toast in a couple of minutes. Mike right too. Clean em to death with haphazzard stroking. Sooooo.......We have intense over capacity loads causing heat and corrosion and erosion in throat/barrel. Kill em with rapid fire shooting....or full auto without cooling breaks. Again, corrosion/erosion of throat and barrel. Wear em with cleaning rods, stainless brushes etc. Any and/or all of the above. Sam

May 12, 2002, 10:31 PM	#13
Archie Senior Member Join Date: May 26, 2000 Location: Hastings, Nebrasksa - the Hear Posts: 2,209	Heat is primary culprit. The burn temperature in a high power rifle is around 4000 - 5000 degrees. That's cutting torch temperature. That's what blows out the leade section, anyway. Bad cleaning will rot out the rest of the bore. __________________ There ain't no free lunch, except Jesus. Archie Check out updated journal at http://oldmanmontgomery.wordpress.com/

May 13, 2002, 12:30 PM	#14
Bogie Senior Member Join Date: June 5, 2000 Location: Job hunting on the road... Posts: 3,827	Bad cleaning, or not enough cleaning. As you fire rounds, you're also eroding the throat, and pressure/heat scarring the first few inches. As this roughens, the barrel will become erratic. __________________ Job hunting, but helping a friend out at www.vikingmachineusa.com - and learning the finer aspects of becoming a precision machinist. And making the world's greatest bottle openers!

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