Barrels o’ Fun

Discussion in 'General Rifle' started by Kellen, Oct 29, 2020.

  1. Kellen

    Kellen G&G Evangelist

    I have a quality Sauer & Sohn rifle from Germany which has a permanently attached barrel using what they call a “heat lock” process (you may know it more commonly under the name “thermal interference fitting”). It is a benefit to accuracy due to high levels of concentricity, but also means that once the throat of that barrel is shot-out then the entire rifle is kaput. No barrel replacement.

    Because of how it was manufactured I don’t much shoot that Sauer & Sohn rifle, even though it is the most accurate rifle I own. I hate to be limited that way, but it’s a gem and I want to stretch its usable life for years ahead.

    That rifle also led me to learn more about barrel life. It’s an interesting topic. Consider for a moment that if you’re lucky enough to have a barrel maintain accuracy up to 3,000 rounds, you have really only exposed that barrel to just six seconds of shooting. That’s because it takes a typical bullet only .002 seconds to pass down the length of a 24” barrel (according to scientists at Lawrence Livermore National Laboratory). Of course, every rifle will be different based on calibers, charges, bullet grains, barrel lengths, cleaning habits, etc., but you get the idea.

    If you have a magnum rifle, say something like a 300 Win Mag, accuracy probably won’t last 3,000 rounds. Probably more like 1,000 to 1,500. On the other hand, if you have a 308 Win using 180-grain factory ammo, heck you may be lucky enough to stretch it out to 5,000 rounds, maybe even 10,000 rounds! That would be all of twenty seconds of shooting impact on the barrel.

    Barrels cost money (they’re getting expensive, aren’t they?) and down time, especially for match shooters, so predicting barrel life is something many people have attempted. Look around the net and you’ll find different “overbore” spreadsheets people have created for that purpose. Having a bit of geek gene myself, I decided to build my own predictive model using the following factors (not including twist rate... should I?):
    ֎ Caliber
    ֎ Bullet grains
    ֎ Powder type
    ֎ Powder charge
    ֎ SAAMI max psi
    ֎ Bullet coating
    ֎ Bullet material
    ֎ Barrel length
    ֎ Barrel material
    ֎ Barrel treatment
    ֎ Kitchen sink (sorry, couldn't resist a self-deprecating joke)

    Since it is an intuitive number, my goal is to have a score of 100 serve as a threshold. Barrels below that score are the ones that last longer, above that score and barrels burnout more quickly. It’s all guesswork, of course. I’m still in the process of building the model, and for all I know it won’t be worth crap on a bun, but what the hell, it’s a fun exercise. Once I get some results from the model I’ll post for y’all to see and let me know if it really is just pure crap or something helpful. Thanks.
     
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  2. Ten Man

    Ten Man G&G Evangelist

    I'll be eagerly awaiting your publishing.
     
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  3. Kellen

    Kellen G&G Evangelist

    Well, here's what I came up with. Whether or not it holds a candle to reality is anyone’s guess, but you can be the judge of that based on your personal experience. My threshold measure is a score of 100 = 5,000 shots, so cartridges which have a K-Score higher than 100 are shown with shorter barrel life, and scores below 100 have a longer barrel life. Added some other columns to show velocity, bullet size, and pressure that was used in the calculation. The formula that led to these results included a total of 15 different inputs for each cartridge.

    One thing to note is that throat erosion begins immediately, with the very first shot taken by a rifle. The main threat to barrel longevity is pressurized heat, but many other factors also affect barrel life, especially time to cool between shots (that's a big one). But the question of what constitutes a shot-out barrel, in other words loss of accuracy, is very subjective. For some people, getting within four inches at 100 yards is considered accurate. For others, anything more than a ½-inch 5-shot spread is unacceptable. So accuracy is in the eye of the beholder and tables like this really just offer comparisons.

    Although there is no model that can absolutely predict barrel wear, hopefully the following will be of some interest if nothing else. I'll no doubt do some more adjusting to it based on your comments. Thanks.

    upload_2020-10-31_12-42-46.png
     
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  4. Ten Man

    Ten Man G&G Evangelist

    I'm having a difficult time believing a 22-250 has a better K Score than a .308. I have heard numerous shooters complain about the short barrel life of a 22-250, while hardly ever hearing anyone complain about a .308 barrel wear problem.

    Perhaps it is totally subjective on the part of the shooters. Not everyone shoots enough to wear out a barrel, unless it's an AK or AR15. LOL!! These days, with the ammo prices jacked up, we probably won't be hearing about AKs and ARs wearing out, either, because A) They are saving their ammo for "the big one," or B) If they burn out a barrel during "the big one," barrel life will not be what they are talking about, after it's over.
     
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  5. Txhillbilly

    Txhillbilly G&G Evangelist

    The 260 Remington is way off also. Most target shooter's only get 3000 - 3500 rounds before accuracy drops off. If only used as a hunting rifle, the round count would be higher, but most 260's are used as long range target guns.

    Most 22-250 barrels are toast around 2500 rounds. My 22 Creedmoor might get to 1200 - 1300 before I swap it out with the second barrel I ordered with the first one.
     
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  6. BigEd63

    BigEd63 G&G Evangelist

    5,345
    14,604
    Arkansas
    I agree with that.
    Of course my experience with a good barrel life comes from shooting a S A. Inc. Custom Shop National Match M1A and I don't know how many rounds the original owner put through it but in total by me alone must have had at least 5000 rds through it back when there was plentiful and cheap surplus 7 62mmNATO to be had. Still shot great up to the time I sold it.
     
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