Spreadsheet Formula Calculates Useful 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 there is not a lot of historical data.
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 an Excel viewer to open the file.
Click to Download Spreadsheet: Barrel Life Spreadsheet (Lastest 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: 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 hard/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.
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Tags: Barrel, Spreadsheet
Mike,
Is there a reason why the N165 has such a lower heat potential than all the other Vihtavuori powders?
Thanks
You need to accommodate for Barrel Pressure in CUP also. Many manufacture show CUP for most common powder used.
Since many do not have access to the program that calculates pressure , it would be nice to be able to quickly plot barrel life versus pressure. Otherwise great program!
My numbers for powder heat are from QuickLoad. I’m used to using PSI since it’s a real value of measurement. But When I get off nightshift, I’ll look into a CUP/PSI conversion, and consider modifying the sheet to take either. Good idea.
A barrel life-vs-pressure plot(and others) would be an easy addition. I’ll work on it as well.
But please keep in mind folks that my math only represents tweaked rules of thumb used to define consistently claimed accuracy from barrels. Nothing has ever been officially measured as far as I’m aware(like accuracy-vs-shot count-vs-pressure-vs-powder-vs-shot rate-vs-steel grade).
It’s best use is for comparisons.
I think it an excellent guideline, as is the quantifiable overbore index, but just like tire “tread life” there are an infinite number of user-related and equipment tolerance-related variables that will affect the end point.
Thanks for taking the time to share this!
Great comparative tool indeed. Can the barrel life be correlated to the length of throat erosion, how much further out the bullet needs to be seated to touch the lands.
e.g. when the throat is eroded forward .06 or .12 inches, the useful life is over. It is specific measure at least.
i can’t get the dropdown list of the powder heat potential to open up propoly to read all the powders. do you have a list of the powder heat potential for me pleas ?
Are there updated powder heat potential numbers for the new IMR Enduron powders available somewhere? I love this spreadsheet for deciding on my pet loads.