Barrel-maker Dan Lilja’s website, RifleBarrels.com has an excellent FAQ page that contains a wealth of useful information. On the Lilja FAQ Page you’ll find answers to many commonly-asked questions. For example, Dan’s FAQ addresses the question of barrel life. Dan looks at factors that affect barrel longevity, and provides some predictions for barrel life, based on caliber, chambering, and intended use.

NOTE: This article was very well-received when it was first published. We are reprising it for the benefit of readers who missed it the first time.

Dan cautions that “Predicting barrel life is a complicated, highly variable subject — there is not a simple answer. Signs of accurate barrel life on the wane are increased copper fouling, lengthened throat depth, and decreased accuracy.” Dan also notes that barrels can wear prematurely from heat: “Any fast varmint-type cartridge can burn out a barrel in just a few hundred rounds if those rounds are shot one after another without letting the barrel cool between groups.”

Q. What Barrel Life, in number of rounds fired, can I expect from my new barrel?

A: That is a good question, asked often by our customers. But again there is not a simple answer. In my opinion there are two distinct types of barrel life. Accurate barrel life is probably the type most of us are referencing when we ask the question. But there is also absolute barrel life too. That is the point where a barrel will no longer stabilize a bullet and accuracy is wild. The benchrest shooter and to a lesser extent other target shooters are looking at accurate barrel life only when asking this question. To a benchrest shooter firing in matches where group size is the only measure of precision, accuracy is everything. But to a score shooter firing at a target, or bull, that is larger than the potential group size of the rifle, it is less important. And to the varmint hunter shooting prairie dog-size animals, the difference between a .25 MOA rifle or one that has dropped in accuracy to .5 MOA may not be noticeable in the field.

The big enemy to barrel life is heat. A barrel looses most of its accuracy due to erosion of the throat area of the barrel. Although wear on the crown from cleaning can cause problems too. The throat erosion is accelerated by heat. Any fast varmint-type cartridge can burn out a barrel in just a few hundred rounds if those rounds are shot one after another without letting the barrel cool between groups. A cartridge burning less powder will last longer or increasing the bore size for a given powder volume helps too. For example a .243 Winchester and a .308 Winchester both are based on the same case but the .308 will last longer because it has a larger bore.

And stainless steel barrels will last longer than chrome-moly barrels. This is due to the ability of stainless steel to resist heat erosion better than the chrome-moly steel.

Barrel Life Guidelines by Caliber and Cartridge Type
As a very rough rule of thumb I would say that with cartridges of .222 Remington size you could expect an accurate barrel life of 3000-4000 rounds. And varmint-type accuracy should be quite a bit longer than this.

For medium-size cartridges, such as the .308 Winchester, 7×57 and even the 25-06, 2000-3000 rounds of accurate life is reasonable.

Hot .224 caliber-type cartridges will not do as well, and 1000-2500 rounds is to be expected.

Bigger magnum hunting-type rounds will shoot from 1500-3000 accurate rounds. But the bigger 30-378 Weatherby types won’t do as well, being closer to the 1500-round figure.

These numbers are based on the use of stainless steel barrels. For chrome-moly barrels I would reduce these by roughly 20%.

The .17 and .50 calibers are rules unto themselves and I’m pressed to predict a figure.

The best life can be expected from the 22 long rifle (.22 LR) barrels with 5000-10,000 accurate rounds to be expected. We have in our shop one our drop-in Anschutz barrels that has 200,000 rounds through it and the shooter, a competitive small-bore shooter reported that it had just quit shooting.

Remember that predicting barrel life is a complicated, highly variable subject. You are the best judge of this with your particular barrel. Signs of accurate barrel life on the wane are increased copper fouling, lengthened throat depth, and decreased accuracy.

Benchrest Barrel Life — You May Be Surprised
I thought it might be interesting to point out a few exceptional Aggregates that I’ve fired with 6PPC benchrest rifles with barrels that had thousands of rounds through them. I know benchrest shooters that would never fire barrels with over 1500 shots fired in them in registered benchrest matches.

I fired my smallest 100-yard 5-shot Aggregate ever in 1992 at a registered benchrest match in Lewiston, Idaho. It was a .1558″ aggregate fired in the Heavy Varmint class. And that barrel had about 2100 rounds through it at the time.

Another good aggregate was fired at the 1997 NBRSA Nationals in Phoenix, Arizona during the 200-yard Light Varmint event. I placed second at this yardage with a 6PPC barrel that had over 2700 rounds through it at the time. I retired this barrel after that match because it had started to copper-foul quite a bit. But accuracy was still good.

This thought-provoking article is one of the 15 most popular Daily Bulletin features over the last 12 months. We are republishing this story today for readers who may have missed it the first time around…

Here’s a little known fact that may startle most readers, even experienced gunsmiths: your barrel wears out in a matter of seconds. The useful life of a typical match barrel, in terms of actual bullet-in-barrel time, is only a few seconds. How can that be, you ask? Well you need to look at the actual time that bullets spend traveling through the bore during the barrel’s useful life. (Hint: it’s not very long).

Bullet-Time-in-Barrel Calculations
If a bullet flies at 3000 fps, it will pass through a 24″ (two-foot) barrel in 1/1500th of a second. If you have a useful barrel life of 3000 rounds, that would translate to just two seconds of actual bullet-in-barrel operating time.

Ah, but it’s not that simple. Your bullet starts at zero velocity and then accelerates as it passes through the bore, so the projectile’s average velocity is not the same as the 3000 fps muzzle velocity. So how long does a centerfire bullet (with 3000 fps MV) typically stay in the bore? The answer is about .002 seconds. This number was calculated by Varmint Al, who is a really smart engineer dude who worked at the Lawrence Livermore Laboratory, a government think tank that develops neutron bombs, fusion reactors and other simple stuff.

On his Barrel Tuner page, Varmint Al figured out that the amount of time a bullet spends in a barrel during firing is under .002 seconds. Al writes: “The approximate time that it takes a 3300 fps muzzle velocity bullet to exit the barrel, assuming a constant acceleration, is 0.0011 seconds. Actual exit times would be longer since the bullet is not under constant acceleration.”

We’ll use the .002 number for our calculations here, knowing that the exact number depends on barrel length and muzzle velocity. But .002 is a good average that errs, if anything, on the side of more barrel operating life rather than less.

So, if a bullet spends .002 seconds in the barrel during each shot, and you get 3000 rounds of accurate barrel life, how much actual firing time does the barrel deliver before it loses accuracy? That’s simple math: 3000 x .002 seconds = 6 seconds.

Gone in Six Seconds. Want to Cry Now?
Six seconds. That’s how long your barrel actually functions (in terms of bullet-in-barrel shot time) before it “goes south”. Yes, we know some barrels last longer than 3000 rounds. On the other hand, plenty of .243 Win and 6.5-284 barrels lose accuracy in 1500 rounds or less. If your barrel loses accuracy at the 1500-round mark, then it only worked for three seconds! Of course, if you are shooting a “long-lived” .308 Win that goes 5000 rounds before losing accuracy, then you get a whopping TEN seconds of barrel life. Anyway you look at it, a rifle barrel has very little longevity, when you consider actual firing time.

People already lament the high cost of replacing barrels. Now that you know how short-lived barrels really are, you can complain even louder. Of course our analysis does give you even more of an excuse to buy a nice new Bartlein, Krieger, Shilen etc. barrel for that fine rifle of yours.

Can sustained rapid-fire shooting with no cool-down period wear out a quality barrel more quickly? The answer is “Yes” according to Forum member LCazador, who did an interesting comparison test with two .243 Winchester barrels. He started off with two, identical, match-grade HV taper stainless barrels. Both were NEW at the start of testing, and LCazador shot the same load through each: 95gr match bullets with 38 grains of Hodgdon Varget. After giving both barrels the same, gentle 20-round break-in, 300 rounds were then fired through each barrel — in very different ways. Barrel condition and wear were monitored with a borescope.

Barrel One — Slow Fire, Cool Down Periods, Cleaning Every 50 Rounds
At the end of the 300-round test, Barrel One looked brand new. There was none of the severe fire cracking found in Barrel Two. This barrel was shot no more than 10 times without a cool down and firing was done at a much slower pace. Cleaning for this barrel was done every 50 shots.

Barrel Two — Fast Firing, No Waiting, Cleaning Every 100 Rounds
The second barrel, which received hard use and minimal cleaning, was severely damaged with severe fire cracking at the leade and throat. As a result, the barrel had to be re-chambered. This barrel was shot 100 rounds at time without cleaning and was shot up to 20 times in succession without a cool down.

LESSON LEARNED — Heat Kills Barrel Life
Don’t let your barrel get too hot, and keep it clean. One afternoon can ruin a barrel!

Monitoring Barrel Wear with Borescope
Some folks worry too much about what their borescopes reveal — many barrels do not have to be “squeaky clean” to perform well. In fact some barrels run better after ten or more fouling shots. However, a borescope can be very helpful when your barrel starts losing accuracy for no apparent reason. Forum member FdShuster writes:

“A borescope is a positive way of backing up your suspicions when the rifle starts to throw an occasional (soon followed by more frequent) wild shot. Using the scope is also an excellent way to determine that the cause is barrel wear and not simply a need for a concentrated cleaning session to remove built up copper and more importantly, carbon fouling.

I’ve had a few barrels that gave every indication of being shot out. But I ‘scoped them out and found the cause to be nothing more than requiring a good cleaning. They then returned to their usual performance. There’s no guessing involved when you are able to get ‘up close and personal’ using the scope. The borescope also provides an excellent view of the all-important condition of the crown. My borescope is one of the most valuable investments I’ve ever made.”

This thought-provoking article is one of the 15 most popular Daily Bulletin features over the last 12 months. We are republishing this story today for readers who may have missed it the first time around…

Here’s a little known fact that may startle most readers, even experienced gunsmiths: your barrel wears out in a matter of seconds. The useful life of a typical match barrel, in terms of actual bullet-in-barrel time, is only a few seconds. How can that be, you ask? Well you need to look at the actual time that bullets spend traveling through the bore during the barrel’s useful life. (Hint: it’s not very long).

Bullet-Time-in-Barrel Calculations
If a bullet flies at 3000 fps, it will pass through a 24″ (two-foot) barrel in 1/1500th of a second. If you have a useful barrel life of 3000 rounds, that would translate to just two seconds of actual bullet-in-barrel operating time.

Ah, but it’s not that simple. Your bullet starts at zero velocity and then accelerates as it passes through the bore, so the projectile’s average velocity is not the same as the 3000 fps muzzle velocity. So how long does a centerfire bullet (with 3000 fps MV) typically stay in the bore? The answer is about .002 seconds. This number was calculated by Varmint Al, who is a really smart engineer dude who worked at the Lawrence Livermore Laboratory, a government think tank that develops neutron bombs, fusion reactors and other simple stuff.

On his Barrel Tuner page, Varmint Al figured out that the amount of time a bullet spends in a barrel during firing is under .002 seconds. Al writes: “The approximate time that it takes a 3300 fps muzzle velocity bullet to exit the barrel, assuming a constant acceleration, is 0.0011 seconds. Actual exit times would be longer since the bullet is not under constant acceleration.”

We’ll use the .002 number for our calculations here, knowing that the exact number depends on barrel length and muzzle velocity. But .002 is a good average that errs, if anything, on the side of more barrel operating life rather than less.

So, if a bullet spends .002 seconds in the barrel during each shot, and you get 3000 rounds of accurate barrel life, how much actual firing time does the barrel deliver before it loses accuracy? That’s simple math: 3000 x .002 seconds = 6 seconds.

Gone in Six Seconds. Want to Cry Now?
Six seconds. That’s how long your barrel actually functions (in terms of bullet-in-barrel shot time) before it “goes south”. Yes, we know some barrels last longer than 3000 rounds. On the other hand, plenty of .243 Win and 6.5-284 barrels lose accuracy in 1500 rounds or less. If your barrel loses accuracy at the 1500-round mark, then it only worked for three seconds! Of course, if you are shooting a “long-lived” .308 Win that goes 5000 rounds before losing accuracy, then you get a whopping TEN seconds of barrel life. Anyway you look at it, a rifle barrel has very little longevity, when you consider actual firing time.

People already lament the high cost of replacing barrels. Now that you know how short-lived barrels really are, you can complain even louder. Of course our analysis does give you even more of an excuse to buy a nice new Bartlein, Krieger, Shilen etc. barrel for that fine rifle of yours.

Barrel-maker Dan Lilja’s website, RifleBarrels.com has an excellent FAQ page that contains a wealth of useful information. On the Lilja FAQ Page you’ll find answers to many commonly-asked questions. For example, Dan’s FAQ addresses the question of barrel life. Dan looks at factors that affect barrel longevity, and provides some predictions for barrel life, based on caliber, chambering, and intended use.

NOTE: This article was very well-received when it was first published. We are reprising it for the benefit of readers who missed it the first time.

Dan cautions that “Predicting barrel life is a complicated, highly variable subject — there is not a simple answer. Signs of accurate barrel life on the wane are increased copper fouling, lengthened throat depth, and decreased accuracy.” Dan also notes that barrels can wear prematurely from heat: “Any fast varmint-type cartridge can burn out a barrel in just a few hundred rounds if those rounds are shot one after another without letting the barrel cool between groups.”

Q. What Barrel Life, in number of rounds fired, can I expect from my new barrel?

A: That is a good question, asked often by our customers. But again there is not a simple answer. In my opinion there are two distinct types of barrel life. Accurate barrel life is probably the type most of us are referencing when we ask the question. But there is also absolute barrel life too. That is the point where a barrel will no longer stabilize a bullet and accuracy is wild. The benchrest shooter and to a lesser extent other target shooters are looking at accurate barrel life only when asking this question. To a benchrest shooter firing in matches where group size is the only measure of precision, accuracy is everything. But to a score shooter firing at a target, or bull, that is larger than the potential group size of the rifle, it is less important. And to the varmint hunter shooting prairie dog-size animals, the difference between a .25 MOA rifle or one that has dropped in accuracy to .5 MOA may not be noticeable in the field.

The big enemy to barrel life is heat. A barrel looses most of its accuracy due to erosion of the throat area of the barrel. Although wear on the crown from cleaning can cause problems too. The throat erosion is accelerated by heat. Any fast varmint-type cartridge can burn out a barrel in just a few hundred rounds if those rounds are shot one after another without letting the barrel cool between groups. A cartridge burning less powder will last longer or increasing the bore size for a given powder volume helps too. For example a .243 Winchester and a .308 Winchester both are based on the same case but the .308 will last longer because it has a larger bore.

And stainless steel barrels will last longer than chrome-moly barrels. This is due to the ability of stainless steel to resist heat erosion better than the chrome-moly steel.

Barrel Life Guidelines by Caliber and Cartridge Type
As a very rough rule of thumb I would say that with cartridges of .222 Remington size you could expect an accurate barrel life of 3000-4000 rounds. And varmint-type accuracy should be quite a bit longer than this.

For medium-size cartridges, such as the .308 Winchester, 7×57 and even the 25-06, 2000-3000 rounds of accurate life is reasonable.

Hot .224 caliber-type cartridges will not do as well, and 1000-2500 rounds is to be expected.

Bigger magnum hunting-type rounds will shoot from 1500-3000 accurate rounds. But the bigger 30-378 Weatherby types won’t do as well, being closer to the 1500-round figure.

These numbers are based on the use of stainless steel barrels. For chrome-moly barrels I would reduce these by roughly 20%.

The .17 and .50 calibers are rules unto themselves and I’m pressed to predict a figure.

The best life can be expected from the 22 long rifle (.22 LR) barrels with 5000-10,000 accurate rounds to be expected. We have in our shop one our drop-in Anschutz barrels that has 200,000 rounds through it and the shooter, a competitive small-bore shooter reported that it had just quit shooting.

Remember that predicting barrel life is a complicated, highly variable subject. You are the best judge of this with your particular barrel. Signs of accurate barrel life on the wane are increased copper fouling, lengthened throat depth, and decreased accuracy.

Benchrest Barrel Life — You May Be Surprised
I thought it might be interesting to point out a few exceptional Aggregates that I’ve fired with 6PPC benchrest rifles with barrels that had thousands of rounds through them. I know benchrest shooters that would never fire barrels with over 1500 shots fired in them in registered benchrest matches.

I fired my smallest 100-yard 5-shot Aggregate ever in 1992 at a registered benchrest match in Lewiston, Idaho. It was a .1558″ aggregate fired in the Heavy Varmint class. And that barrel had about 2100 rounds through it at the time.

Another good aggregate was fired at the 1997 NBRSA Nationals in Phoenix, Arizona during the 200-yard Light Varmint event. I placed second at this yardage with a 6PPC barrel that had over 2700 rounds through it at the time. I retired this barrel after that match because it had started to copper-foul quite a bit. But accuracy was still good.

This thought-provoking article has been one of the most popular Daily Bulletin features in recent years. We are republishing this story today for readers who may have missed it the first time around…

Here’s a little known fact that may startle most readers, even experienced gunsmiths: your barrel wears out in a matter of seconds. The useful life of a typical match barrel, in terms of actual bullet-in-barrel time, is only a few seconds. How can that be, you ask? Well you need to look at the actual time that bullets spend traveling through the bore during the barrel’s useful life. (Hint: it’s not very long).

Bullet-Time-in-Barrel Calculations
If a bullet flies at 3000 fps, it will pass through a 24″ (two-foot) barrel in 1/1500th of a second. If you have a useful barrel life of 3000 rounds, that would translate to just two seconds of actual bullet-in-barrel operating time.

Ah, but it’s not that simple. Your bullet starts at zero velocity and then accelerates as it passes through the bore, so the projectile’s average velocity is not the same as the 3000 fps muzzle velocity. So how long does a centerfire bullet (with 3000 fps MV) typically stay in the bore? The answer is about .002 seconds. This number was calculated by Varmint Al, who is a really smart engineer dude who worked at the Lawrence Livermore Laboratory, a government think tank that develops neutron bombs, fusion reactors and other simple stuff.

On his Barrel Tuner page, Varmint Al figured out that the amount of time a bullet spends in a barrel during firing is under .002 seconds. Al writes: “The approximate time that it takes a 3300 fps muzzle velocity bullet to exit the barrel, assuming a constant acceleration, is 0.0011 seconds. Actual exit times would be longer since the bullet is not under constant acceleration.”

We’ll use the .002 number for our calculations here, knowing that the exact number depends on barrel length and muzzle velocity. But .002 is a good average that errs, if anything, on the side of more barrel operating life rather than less.

So, if a bullet spends .002 seconds in the barrel during each shot, and you get 3000 rounds of accurate barrel life, how much actual firing time does the barrel deliver before it loses accuracy? That’s simple math: 3000 x .002 seconds = 6 seconds.

Gone in Six Seconds. Want to Cry Now?
Six seconds. That’s how long your barrel actually functions (in terms of bullet-in-barrel shot time) before it “goes south”. Yes, we know some barrels last longer than 3000 rounds. On the other hand, plenty of .243 Win and 6.5-284 barrels lose accuracy in 1500 rounds or less. If your barrel loses accuracy at the 1500-round mark, then it only worked for three seconds! Of course, if you are shooting a “long-lived” .308 Win that goes 5000 rounds before losing accuracy, then you get a whopping TEN seconds of barrel life. Anyway you look at it, a rifle barrel has very little longevity, when you consider actual firing time.

People already lament the high cost of replacing barrels. Now that you know how short-lived barrels really are, you can complain even louder. Of course our analysis does give you even more of an excuse to buy a nice new Bartlein, Krieger, Shilen etc. barrel for that fine rifle of yours.

Barrel-maker Dan Lilja’s website has an excellent FAQ page that contains a wealth of useful information. On the Lilja FAQ Page as you’ll find informed answers to many commonly-asked questions. For example, Dan’s FAQ addresses the question of barrel life. Dan looks at factors that affect barrel longevity, and provides some predictions for barrel life, based on caliber, chambering, and intended use.

NOTE: This article was very well-received when it was first published last year. We are reprising it for the benefit of readers who missed it the first time.

Dan cautions that “Predicting barrel life is a complicated, highly variable subject — there is not a simple answer. Signs of accurate barrel life on the wane are increased copper fouling, lengthened throat depth, and decreased accuracy.” Dan also notes that barrels can wear prematurely from heat: “Any fast varmint-type cartridge can burn out a barrel in just a few hundred rounds if those rounds are shot one after another without letting the barrel cool between groups.”

Q. What Barrel Life, in number of rounds fired, can I expect from my new barrel?

A: That is a good question, asked often by our customers. But again there is not a simple answer. In my opinion there are two distinct types of barrel life. Accurate barrel life is probably the type most of us are referencing when we ask the question. But there is also absolute barrel life too. That is the point where a barrel will no longer stabilize a bullet and accuracy is wild. The benchrest shooter and to a lesser extent other target shooters are looking at accurate barrel life only when asking this question. To a benchrest shooter firing in matches where group size is the only measure of precision, accuracy is everything. But to a score shooter firing at a target, or bull, that is larger than the potential group size of the rifle, it is less important. And to the varmint hunter shooting prairie dog-size animals, the difference between a .25 MOA rifle or one that has dropped in accuracy to .5 MOA may not be noticeable in the field.

The big enemy to barrel life is heat. A barrel looses most of its accuracy due to erosion of the throat area of the barrel. Although wear on the crown from cleaning can cause problems too. The throat erosion is accelerated by heat. Any fast varmint-type cartridge can burn out a barrel in just a few hundred rounds if those rounds are shot one after another without letting the barrel cool between groups. A cartridge burning less powder will last longer or increasing the bore size for a given powder volume helps too. For example a .243 Winchester and a .308 Winchester both are based on the same case but the .308 will last longer because it has a larger bore.

And stainless steel barrels will last longer than chrome-moly barrels. This is due to the ability of stainless steel to resist heat erosion better than the chrome-moly steel.

Barrel Life Guidelines by Caliber and Cartridge Type
As a very rough rule of thumb I would say that with cartridges of .222 Remington size you could expect an accurate barrel life of 3000-4000 rounds. And varmint-type accuracy should be quite a bit longer than this.

For medium-size cartridges, such as the .308 Winchester, 7×57 and even the 25-06, 2000-3000 rounds of accurate life is reasonable.

Hot .224 caliber-type cartridges will not do as well, and 1000-2500 rounds is to be expected.

Bigger magnum hunting-type rounds will shoot from 1500-3000 accurate rounds. But the bigger 30-378 Weatherby types won’t do as well, being closer to the 1500-round figure.

These numbers are based on the use of stainless steel barrels. For chrome-moly barrels I would reduce these by roughly 20%.

The .17 and .50 calibers are rules unto themselves and I’m pressed to predict a figure.

The best life can be expected from the 22 long rifle (.22 LR) barrels with 5000-10,000 accurate rounds to be expected. We have in our shop one our drop-in Anschutz barrels that has 200,000 rounds through it and the shooter, a competitive small-bore shooter reported that it had just quit shooting.

Remember that predicting barrel life is a complicated, highly variable subject. You are the best judge of this with your particular barrel. Signs of accurate barrel life on the wane are increased copper fouling, lengthened throat depth, and decreased accuracy.

Benchrest Barrel Life — You May Be Surprised
I thought it might be interesting to point out a few exceptional Aggregates that I’ve fired with 6PPC benchrest rifles with barrels that had thousands of rounds through them. I know benchrest shooters that would never fire barrels with over 1500 shots fired in them in registered benchrest matches.

I fired my smallest 100-yard 5-shot Aggregate ever in 1992 at a registered benchrest match in Lewiston, Idaho. It was a .1558″ aggregate fired in the Heavy Varmint class. And that barrel had about 2100 rounds through it at the time.

Another good aggregate was fired at the 1997 NBRSA Nationals in Phoenix, Arizona during the 200-yard Light Varmint event. I placed second at this yardage with a 6PPC barrel that had over 2700 rounds through it at the time. I retired this barrel after that match because it had started to copper-foul quite a bit. But accuracy was still good.

What is “Overbore”? That’s a question rifle shooters can debate to no end. This article from our archives proposes one way to identify “overbore cartridges”. We think the approach outlined here is quite useful, but we know that there are other ways to define cartridges with “overbore” properties. Whenever we run this article, it stimulates a healthy debate among our readers — and that is probably a good thing.

Forum Member John L. has been intrigued by the question of “overbore” cartridges. People generally agree that overbore designs can be “barrel burners”, but is there a way to predict barrel life based on how radically a case is “overbore”? John notes that there is no generally accepted definition of “overbore”. Based on analyses of a wide variety of cartridges, John hoped to create a comparative index to determine whether a cartridge is more or less “overbore”. This, in turn, might help us predict barrel life and maybe even predict the cartridge’s accuracy potential.

John tells us: “I have read countless discussions about overbore cartridges for years. There seemed to be some widely accepted, general rules of thumb as to what makes a case ‘overbore’. In the simplest terms, a very big case pushing a relatively small diameter bullet is acknowledged as the classic overbore design. But it’s not just large powder capacity that creates an overbore situation — it is the relationship between powder capacity and barrel bore diameter. Looking at those two factors, we can express the ‘Overbore Index’ as a mathematical formula — 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.”

OVERBORE INDEX Chart

So what do these numbers mean? John says: “My own conclusion from much reading and analysis is that cartridges with case volume to bore area ratio less than 900 are most likely easy on barrels and those greater than 1000 are hard on barrels.” John acknowledges, however, that these numbers are just for comparison purposes. One can’t simply use the Index number, by itself, to predict barrel life. For example, one cannot conclude that a 600 Index number cartridge will necessarily give twice the barrel life of a 1200 Index cartridge. However, John says, a lower index number “seems to be a good predictor of barrel life”.

John’s system, while not perfect, does give us a benchmark to compare various cartridge designs. If, for example, you’re trying to decide between a 6.5-284 and a 260 Remington, it makes sense to compare the “Overbore Index” number for both cartridges. Then, of course, you have to consider other factors such as powder type, pressure, velocity, bullet weight, and barrel hardness.

Overbore Cases and Accuracy
Barrel life may not be the only thing predicted by the ratio of powder capacity to bore cross-section area. John thinks that if we look at our most accurate cartridges, such as the 6 PPC, and 30 BR, there’s some indication that lower Index numbers are associated with greater inherent accuracy. This is only a theory. John notes: “While I do not have the facilities to validate the hypothesis that the case capacity to bore area ratio is a good predictor of accuracy — along with other well-known factors — it seems to be one important factor.”

For years, many shooters have coated bullets with Moly (molybdenum disulfide) or Danzac (tungsten disulfide or “WS2″). The idea was to reduce friction between bullets and barrel. In theory, this could lengthen barrel life and extend the number of rounds a shooter can fire between cleanings.

Moly and WS2 both have their fans, but in recent years, many guys have switched to Hexagonal Boron Nitride (HBN), another dry lubricant. The advantage of HBN is that it won’t combine with moisture to create harmful acids. HBN is very slippery and it goes on clear, so it doesn’t leave a dirty mess on your hands or loading bench. Typically, HBN is applied via impact plating (tumbling), just as with Moly.

Good Source for Hexagonal Boron Nitride (HBN)
Paul Becigneul (aka PBike in our Forum) has been using HBN for many years with good results. He obtains his HBN from Momentive Performance Materials:

Momentive Performance Materials
www.Momentive.com

Sales Contact: Robert Bell
Sales Email: robert.bell [at] momentive.com
Sales Phone: Robert Bell, (980) 231-5404

HBN Results — Both on Bullets and Barrel Bores
Many folks have asked, “Does Hexagonal Boron Nitride really work?” You’ll find answers to that and many other questions on gunsmith Stan Ware’s popular Bench-Talk.com Blog. There Paul Becigneul (aka Pbike) gives a detailed run-down on HBN use, comparing it to other friction-reducers. Paul also discusses the use of HBN in suspension to pre-coat the inside of barrels. Paul observes:

We coated our bullets … how we had been coating with WS2. Now our bullets have a slightly white sheen to them with kind of like a pearl coat. They are so slippery it takes a little practice to pick them up and not drop them on the trailer floor. What have we noticed down range? Nothing different from WS2 other than the black ring on your target around the bullet hole is now white or nonexistent. Our barrels clean just as clean as with WS2. Your hands aren’t black at the end of the day of shooting and that might be the most important part.

Interestingly, Becigneul decided to try a solution of HBN in alcohol, to pre-coat the inside of barrels. Paul had previously used a compound called Penephite to coat the inside of his barrels after cleaning. Paul explains:

If Penephite was used because it was slippery wouldn’t HBN be better? … We called Momentive again [our source for HBN], and talked about mixing HBN and 90% alcohol for a suspension agent to pre-lube our barrels. He though it sounded great but that the AC6111 Grade HBN would be better for this use. It would stand up in the alcohol suspension and cling to the barrel when passed through on a patch. We got some and mixed it in alcohol 90%. We use about one teaspoon in 16 ounces of alcohol.

We started using it this fall and what we have noticed is that now that first shot fired out of a clean and pre-lubed barrel can be trusted as the true impact point. We use tuners so now I got to the line, fire two shots judge my group for vertical, adjust the tuner as needed or not, and after tune has been achieved go to my record targets. This use has saved us in time at the bench and bullets in the backstop.

You really should read the whole article by Becigneul. He discusses the use of barrel lubes such as Penephite and “Lock-Ease” in some detail. Paul also provides links to HBN vendors and to the Material Safety Data Sheets (MSDS) for the various compounds he tested.

Can sustained rapid-fire shooting with no cool-down period wear out a quality barrel more quickly? The answer is “Yes” according to Forum member LCazador, who did an interesting comparison test with two .243 Winchester barrels. He started off with two, identical, match-grade HV taper stainless barrels. Both were NEW at the start of testing, and LCazador shot the same load through each: 95gr match bullets with 38 grains of Hodgdon Varget. After giving both barrels the same, gentle 20-round break-in, 300 rounds were then fired through each barrel — in very different ways. Barrel condition and wear were monitored with a borescope.

Barrel One — Slow Fire, Cool Down Periods, Cleaning Every 50 Rounds
At the end of the 300-round test, Barrel One looked brand new. There was none of the severe fire cracking found in Barrel Two. This barrel was shot no more than 10 times without a cool down and firing was done at a much slower pace. Cleaning for this barrel was done every 50 shots.

Barrel Two — Fast Firing, No Waiting, Cleaning Every 100 Rounds
The second barrel, which received hard use and minimal cleaning, was severely damaged with severe fire cracking at the leade and throat. As a result, the barrel had to be re-chambered. This barrel was shot 100 rounds at time without cleaning and was shot up to 20 times in succession without a cool down.

LESSON LEARNED — Heat Kills Barrel Life
Don’t let your barrel get too hot, and keep it clean. One afternoon can ruin a barrel!

Monitoring Barrel Wear with Borescope
Some folks worry too much about what their borescopes reveal — many barrels do not have to be “squeaky clean” to perform well. In fact some barrels run better after ten or more fouling shots. However, a borescope can be very helpful when your barrel starts losing accuracy for no apparent reason. Forum member FdShuster writes:

“A borescope is a positive way of backing up your suspicions when the rifle starts to throw an occasional (soon followed by more frequent) wild shot. Using the scope is also an excellent way to determine that the cause is barrel wear and not simply a need for a concentrated cleaning session to remove built up copper and more importantly, carbon fouling.

I’ve had a few barrels that gave every indication of being shot out. But I ‘scoped them out and found the cause to be nothing more than requiring a good cleaning. They then returned to their usual performance. There’s no guessing involved when you are able to get ‘up close and personal’ using the scope. The borescope also provides an excellent view of the all-important condition of the crown. My borescope is one of the most valuable investments I’ve ever made.”