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December 30th, 2014
We can predict, with some certainty, how long a light bulb will last (in use), or a shingle roof, or even a nuclear reactor. But how about barrels? Is there a way to reliably estimate barrel life based on known characteristics? This article explains one effort to quantify barrel life…
 How long will a barrel last before the accuracy “goes south”? There are so many variables involved (powder type, bore diameter, bullet coatings etc.) that it’s hard to predict. You might say “Well, my buddy has a .243 and he got 1500 rounds before the throat was shot out” — those kind of comparisons can be useful, but they’re not very scientific, and they won’t help much if you’ve got a gun in a new chambering (such as the 6.5×47) for which long-term test results are lacking.
Is there a more reliable way to predict barrel life — one that will work for a broad range of calibers? Well, Forum member MikeCr has developed an Excel spreadsheet that accounts for a number of variables, and gives a pretty good estimate of useful barrel life, whether you’re shooting a .223 Rem or a 338 Lapua Magnum. Mike’s program predicts barrel life using five variables: 1) Bullet Diameter; 2) Powder Charge weight; 3) Powder Heat Potential (KJ/kg); 4) Pressure (in psi); and 5) Bullet Coating (yes/no). Mike provides a table with Heat Potential ratings for most popular powder types. The user needs to know the pressure of his load. This can be estimated with QuickLOAD.
You can download the lastest version of Mike’s spreadsheet below. You’ll need Excel or an Excel viewer to open the file.
Click to Download Spreadsheet: Barrel Life Spreadsheet (Latest Version)
Shown below is Mike’s Spreadsheet, with variables for a 6BR shooting 105gr “naked” bullets with 30.3 grains of Hodgdon Varget powder. The formula predicts 2401 rounds of barrel life. That corresponds pretty well to what we’d expect for a 6BR — about 2500 rounds.
 
Mike observes: “There has been a lot of discussion lately related to cartridge design and resulting barrel life. This is a really important factor to consider amongst a myriad of choices. Barrel life is controversial, and subjective. There are no clear-cut standards for comparison. But a few years ago, I put together a spreadsheet based on Bart Bobbit’s rule of thumb. It worked pretty good, only occasionally failing some tests when validated against posted barrel lives.
According to Ken Howell, I had to account for pressure. And Henry Child’s powder temperature testing provided another piece needed. So, I’ve tweaked it here and there to pass more tests. From 223 Rem to 300 UltraMagnum. Another element added, but turned off, is shot interval. I would need way more tests to lock in on this. But everyone knows, the faster you shoot, the worse the barrel life.
Anyway, another factor hard to define is ‘accurate’ barrel life. This cannot be quantified without standards. Barrels are replaced when expectations are no longer met. I feel that a [barrel] passes peak potential in a finite period due to throat erosion. But that don’t mean it’s toast, if it still shoots well enough. It’s just as likely that many of us never see that peak potential anyway. It’s a slippery thing. Point-blank BR competitors will toss a barrel when it leaves the 1s. I could get another 4000 rounds from it, and be content with its performance, I’m sure.”
NOTE: Mike says: “This spreadsheet may show a lower barrel life than you prefer. But it pretty well spotlights cartridges to stay away from if you plan much time at the range or in dog town.”
Editor’s Comment: Mike’s spreadsheet is a helpful tool, but it is NOT a definitive “take-it-to-the-bank” indicator of barrel life. Mike cautions that predicting barrel life involves so many different factors (including how hot the barrel is run), that the task is a bit like predicting tread life on car tires. Still, the spreadsheet is very helpful. It can certainly warn us that some chamberings (such as the 6-284) are likely to be barrel burners. That can help you make a smart decision when choosing a chambering for your next rifle.
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March 2nd, 2014
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.”
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April 25th, 2013
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.”
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July 27th, 2012
How long will a barrel last before the accuracy “goes south”? There are so many variables involved (powder type, bore diameter, bullet coatings etc.) that it’s hard to predict. You might say “Well, my buddy has a .243 and he got 1500 rounds before the throat was shot out” — those kind of comparisons can be useful, but they’re not very scientific, and they won’t help much if you’ve got a gun in a new chambering (such as the 6.5×47) for which long-term test results are lacking.
Is there a more reliable way to predict barrel life — one that will work for a broad range of calibers? Well, Forum member MikeCr has developed an Excel spreadsheet that accounts for a number of variables, and gives a pretty good estimate of useful barrel life, whether you’re shooting a .223 Rem or a 338 Lapua Magnum. Mike’s program predicts barrel life using five variables: 1) Bullet Diameter; 2) Powder Charge weight; 3) Powder Heat Potential (KJ/kg); 4) Pressure (in psi); and 5) Bullet Coating (yes/no). Mike provides a table with Heat Potential ratings for most popular powder types. The user needs to know the pressure of his load. This can be estimated with QuickLOAD.
You can download the lastest version of Mike’s spreadsheet below. You’ll need Excel or an Excel viewer to open the file.
Click to Download Spreadsheet: Barrel Life Spreadsheet (Latest Version)
Shown below is Mike’s Spreadsheet, with variables for a 6BR shooting 105gr “naked” bullets with 30.3 grains of Hodgdon Varget powder. The formula predicts 2401 rounds of barrel life. That corresponds pretty well to what we’d expect for a 6BR — about 2500 rounds.
Mike observes: “There has been alot of discussion lately related to cartridge design and resulting barrel life. This is a really important factor to consider amongst a myriad of choices. Barrel life is controversial, and subjective. There are no clear-cut standards for comparison. But a few years ago, I put together a spreadsheet based on Bart Bobbit’s rule of thumb. It worked pretty good, only occasionally failing some tests when validated against posted barrel lives.
According to Ken Howell, I had to account for pressure. And Henry Child’s powder temperature testing provided another piece needed. So, I’ve tweaked it here and there to pass more tests. From 223rem to 300 UltraMagnum. Another element added, but turned off is shot interval. I would need way more tests to lock in on this. But everyone knows, the faster you shoot, the worse the barrel life.
Anyway, another factor hard to define is ‘accurate’ barrel life. This cannot be quantified without standards. Barrels are replaced when expectations are no longer met. I feel that a [barrel] passes peak potential in a finite period due to throat erosion. But that don’t mean it’s toast, if it still shoots well enough. It’s just as likely that many of us never see that peak potential anyway. It’s a slippery thing. Point-blank BR competitors will toss a barrel when it leaves the 1s. I could get another 4000 rounds from it, and be content with its performance, I’m sure.”
NOTE: Mike says: “This spreadsheet may show a lower barrel life than you prefer. But it pretty well spotlights cartridges to stay away from if you plan much time at the range or in dog town.”
Editor’s Comment: We want to stress that Mike’s spreadsheet is a helpful tool, but it is not a definitive “take-it-to-the-bank” indicator of barrel life. Mike cautions that predicting barrel life involves so many different factors (including how hot the barrel is run), that the task is a bit like predicting tread life on car tires. Still, the spreadsheet is very helpful. It can certainly put shooters on notice that some chamberings (such as the 6-284) are likely to be a barrel burners. That can help you make a smart decision when choosing a chambering for your next rifle.
Share the post "Handy Excel Formula Predicts Useful Barrel Life"
May 20th, 2010
 Lapua developed the 6.5×47 Lapua cartridge for International 300m competition. Lapua wanted a cartridge that could match the “pure accuracy” of the 6mmBR, but with even better ballistics and good barrel life. The 6.5x47L is now really coming into its own. In the hands of NBRSA long-range Hall of Famer Don Nielson, the 6.5x47L has won two NBRSA 600-yard Nationals convincingly. The cartridge is winning Varmint Silhouette matches, and Tactical competitors are finding the cartridge delivers great accuracy with much less recoil than a .308 — plus it feeds well from magazines. With advanced powders such as Alliant’s Reloder 17, the 6.5x47L can deliver surprising velocities, even with the heavy 139-142 grain bullets, though we still think the 130-grainers may be optimal for the cartridge. Don Nielson used Berger 130gr bullets “right out of the box” to win the NBRSA 600-yard Nationals, setting records in the process. In addition to its paper-punching abilities, the 6.5×47 Lapua is a capable hunting cartridge, delivering velocities that approach a .260 Remington with 120-130 grain projectiles. Considering all this — is the 6.5×47 Lapua the next, great do-it-all cartridge — a chambering that can win a benchrest match one weekend and harvest a whitetail the next?
6.5×47 Lapua Ballistics Chart | 6.5×47 Lapua Cartridge Diagram (PDF)
6.5×47 Lapua Is a Hot Topic on Our Forum
In our AccurateShooter Forum, there has been a thread discussing whether the 6.5x47L or 6mmBR is better for the 600-yard game. Forum member Lloyd (aka “1Shot”) wrote:
How many years have the 6BR and its variants been in existence as opposed to the 6.5x47L? I pose this question to you because we all know that with time and experience, comes knowledge. In a short period of time, (relatively speaking) the 6.5x47L has made great strides. I’ll make a bet that the 6.5x47L will outshoot the 6BR within the same time frame of its existence. It will just take time and shooters like Sam Hall to bring this cartridge to its full potential.”
Responding to Lloyd’s post, British gun writer Laurie Holland analyzed the present and possible future of the 6.5x47L cartridge. Laurie makes some very interesting points, considering the role the 6.5x47L may play in F-class competition, and in 300 to 600-yard benchrest. Laurie’s post is worth a read….
 Laurie Holland Talks About the 6.5×47 Lapua
“Lloyd, you may well be right on this. There is that intangible something issue though that sees one cartridge become ‘great’ in a shooting field, while others that should theoretically compete somehow never quite get there. The example that comes to mind is the PPC in short range BR of course[.] The PPC outshoots similar rivals, and we don’t know why. At the moment, the 6BR and BRX/Dasher variants look like they may be getting to the same point in 300 to 600-yard BR type competition. That’s not to say they won’t be pushed out of the top spot by something better, or even matched by a rival, but it looks like it won’t happen quickly or soon.
One thing people often forget is that BR can see 5 shots rattled off in under 30 seconds while the wind conditions hold. F-Class or any other form of deliberate, marked-target shooting is different because of the enforced gap between shots. This is particularly so on our side of the Atlantic (or north of the 49th Parallel). Unlike your F-Class, Fullbore, Palma, CLRP etc. shooting, we British Commonwealth types are squadded two to a target (sometimes up to four in local shoots) and there is therefore a minimum three or so minutes between taking each shot by an individual shooter. Fairly typically, I shot in a club 600-yard F-Class comp last Sunday and found myself with two others on ‘my’ target. Throw in one of them missing with both sighters and the resulting delays while the RO had to be asked for the target to be pulled and checked and people looking for his subsequent fall of shot and it took around 70-75 minutes to get through 2 sighters and 20 score shots. So each shot is virtually a new start so far as the wind-call goes.
The 6.5X47L likely gives a significant benefit even at 600 yards over the 6mmBR thanks to the external ballistics improvements in such a scenario. What has to be seen is how it stands up in national level competition against the big sevens since that’s the competition in F-Open. Until this year, all national GB F-Class Association rounds were shot over a mixture of 800, 900, 1000-yard matches with the emphasis on the 1000. The 6.5X47L can’t hack it against 180gr 7mm Berger VLDs at 3,200 fps in these conditions (nor could the US F-Class Team’s 6.5-284 Norma in last summer’s F-Class World Championship at Bisley). Club / regional level may turn out different with a bigger mix of ranges (distances) in a season’s programme. And (here’s the killer) — the 7mmWSM brigade can’t afford to shoot say 15 such matches in a season given the barrel life issue. 15 matches is 300-330 shots, or 50% of barrel life. So they enter one or two matches only for practice, checking sight-settings etc. Unless you do your own gunsmithing, barrel replacement by a top gunsmith with a Bartlein or Krieger tube is an expensive job here — a bit over £700 all in which is $1,000 + in translation[.]
So, accurate and ballistically-efficient smaller cartridges that give long barrel life have a bright future in European and British Commonwealth shooting, and I think the 6.5X47L is going to be a key player in this role. Also, as in the USA, many people want a multi-purpose longarm, and this cartridge is an excellent long-range fox/crow round and ideal for most of our deer species too.
To go back to the very original question in this thread, if I were having a multi-discipline target shooting single-shot rifle built for club / regional competition shooting, I’d stick to 6BR or variants if it were primarily for 600-yard or shorter range competitions, but I’d go for 6.5X47L if there were 800 to 1,000-yard matches in the mix. If it were for F-Class at national level, I’d have neither, but stick to .308W in the F/TR division which I shoot now. — Laurie, York, England”
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