Barrel Life - key factors?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by bookworm, Nov 19, 2011.

  1. bookworm

    bookworm Well-Known Member

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    What is the key factor (or factors) that control barrel life? Is it just bullet velocity or are there others?

    Are there any resources that show expected barrel life range (even rule of thumb) for various calibers?

    As I mull over my caliber options I'm trying to take into account all the important items (cost, recoil, external ballistics, etc.)...but I don't have a good feel for expected barrel life.
     
  2. J E Custom

    J E Custom Well-Known Member

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    Barrel life is based on many things so I take a stab at some well known things that should help.

    The quality of the barrel material, barrel quality, type of powder, volume of powder,chamber
    Pressure, Velocity, efficiency of cartrige, barrel temperature, Etc.

    Cartridges with high pressure, high velocity and that are over bore tend to shorten barrel life.

    Anything over 3000 ft/sec starts to shorten life the faster you go.

    308s are a good example of good barrel life , small powder charge (Most of the powder is
    consumed in the case) velocity between 2500 and 2800ft/sec with most loads.

    7mm with very large cases (264 Win Mag ,7 Rem Mag, 7 STW, 7 Wea Mag, 7 Rum are some
    examples of barrel burners, Of course there are others, these are some of the more notorious
    ones.

    "BUT" with care and good maintenance they can last a lifetime of hunting without any accuracy
    loss.

    The worst case I ever saw was a 7 STW loaded very hard (Almost 3800 ft/sec with a 31" barrel
    lasted between 1100 and 1200 rounds before accuracy fell off.

    The best I have personally seen is /was a 308 target with a 28" hart barrel that will still shoot
    sub 1/2 MOA (With Iron Sights) that has in excess of 23,000 rounds down the tube.(It was used
    in competition for 17 years By 4 different shooters.

    If your talking about a hunting rifle , Don't worry about barrel life. If it is a match rifle
    considerations should be though of based on estimated rounds to be fired through it in
    one year.

    In most cases barrel life is way overrated and should not be a consideration.

    Build what you want.

    J E CUSTOM
     

  3. BountyHunter

    BountyHunter Writers Guild

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    Go to 6mmbr and search the articles section for the barrel life program that estimates barrel life based on your info
     
  4. bookworm

    bookworm Well-Known Member

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    JE - thanks for the input. I'm trying to avoid ending up with a barrel burner. I'm not a competition shooter - I will only put 500 rounds through a barrel in a year, but I'd hate to have to replace the barel after only 2-3 years. I'm really looking for something I can get 5+ years out of...if not longer.

    Bounty - I appreciate the tip. I wasn't able to get the spreadsheet off of the 6mmbr site (too many downloads it looks like), but I was able to find it on the Accurateshooter site. Even if it's not highly accurate it should give me a pretty good idea of where I'd be...very useful.

    Thanks again!
     
  5. Willys46

    Willys46 Well-Known Member

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    It's just like race cars and horse power, it gets expensive to go fast! This is also why most race cars are not daily drivers.

    Build what you want and put barrel life in the back burner, and build your self or buy a daily driver.
    I built a 7 mag and got it dialed in, roughly 150 rounds. And bought a cheaper 308 and shoot the he'll out of it. It's much more difficult to get consistent hits at range with a 308 than a 7 mag. So when I switch back to the 7 it seems easy! This has improved my shooting skills much more than if I would shoot the hot rod.

    This way I have a nice hunting gun that only gets shoot about 50 rounds a year and a 308 that gets shoot 1500 rounds! The 7 will last forever at that pace and the 308 is good for 5+ years.

    As for barrel burring, small bores with big powder charges= short barrel life. Take the same powder charge and start increasing the bore size and the barrel life increases.

    243 win burns out faster than a 260, which burns out faster than a 308. Simple terms.
    264win vs 7mm vs 300 vs 338 Same concept.
     
  6. bookworm

    bookworm Well-Known Member

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    Willys - it's interesting you make this suggestion, as this is the approach I started with in my brain a few months ago but abandoned it because I didn't like the idea of spending money on 2 rifles...so now I've come full circle. I think it makes a lot of sense, so I'm going to seriously consider it again.

    Since it gets most of your rounds, did ou spend some bigger $$ on the .308 to build a custom?
     
  7. Willys46

    Willys46 Well-Known Member

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    This was my approach. Built a nice longrange rig. Bought good glass for it and put a 20 moa base. I spent alot (relative) on glass so I could use it on both my longrange gun and then use it on the 308 in the off season.

    For the 308, I started with a used rem PSS. The nice thing about 308 buying used is ok because barrel life is great. I shoot that setup for over a year. Barrel had over 3000 rounds through it. Because longrange shooting and building guns is a sickness I had a new barrel and stock put on the 308. So now I have a really nice hunting rig and a 308 to shoot. I share the glass between them. Now I shoot the 308 from jan to late aug and then set the hinting rig up and get it dialed in. Takes about 25 rounds to get comfortable again. And have 25 rounds for hunting and target practice during the season.

    Just how I did it. Just remember you can get almost ANY 308 to shoot .75 moa.
     
  8. Bart B

    Bart B Well-Known Member

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    I came up with a formula some years go that seems to me and lots of others to be about right.

    Barrel life will be about 3000 rounds of best accuracy when there's one grain of powder for each square millimeter of the bore's cross section.

    Increase powder charge 40 to 50 percent for that bore diameter and barrel life gets cut in half.

    Double the amount of powder for that caliber and barrel life goes down to about 1/4th as many rounds.

    The above applies to top quality barrels that start out shooting no worse than 1/4 moa at 100 yards. Barrels starting out shooting 1/2 to 1 moa seem to last twice as long; 5000 to 6000 rounds of accuracy at that level.

    And the rest that start out at 1 to 2 MOA at 100 yards will last 10,000 to 12,000 rounds before noticable accuracy drops off. Standard 30 caliber service rifles fall into this categore.

    How well one shoots plays into the observable barrel life. Top accuracy shooters will see a given barrel start going bad sooner than those that aren't so accurate in their shooting skills.

    Sierra Bullets replaces their .308 Win. test barrels as they start shooting 10 shot test groups that go up to about 3/8 moa that happens at about 3000 rounds. They keep several hundred rounds of any lot of bullets that shoot exceptionally well in their rail guns. Some of ther 30 caliber Match Kings would shoot under 2/10ths MOA round after round and they would keep those as "standards" to shoot once in a while to see when their test barrel was going bad. Same for other calibers. Sierra used to put some of those super accurate bullets in plain brown boxes then sell them through two guys at high power rifle matches but that stopped in the early 1990's. They shot much more accurate than the ones they sold in green boxes.

    Compared to .22 rimfire ammo, the US Olympic Team members rebarrel their rifles when they've got about 30,000 rounds through them. Starting out a sub 1/2 moa at 50 meters with a good lot of ammo, they know when bullets start striking too far from where they called the shot.
     
    Last edited: Nov 22, 2011
  9. bookworm

    bookworm Well-Known Member

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    Interesting formula Bart. I want to make sure I get it.

    If I apply it to a .308 I get around 48gr, which isn't too far from a standard load. Based on this...you are saying that a 1/2 moa rifle would shoot at that level for 5000 - 6000 rounds.

    And if I apply it to my .300WM which shoots around 1/2" and takes 78gr of powder...since this is a 62% increase in powder this would translate to something a bit less than half of your standard barrel life - or maybe 2000 to 2500 rounds.

    Do I have that about right?
     
  10. woods

    woods Well-Known Member

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    guideline only

    [​IMG]
     
  11. Bart B

    Bart B Well-Known Member

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    Yes, that's close. But the key element is what the accuracy is of your rifle now. You have to shoot at least 15 shots per test group and 20 is better. Otherwise, the statistical significance, or probability that the group you shoot has at least a 75% chance of being reality. 5-shot groups are only 50% reliable.
     
  12. FAL Shot

    FAL Shot Well-Known Member

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    If you have a hard chrome lined military barrel, it should exceed this chart by quite a bit. I was told my hard chromed barrel on my FAL was good for tens of thousands of rounds if I treated it reasonably well. The receiver has a design life of 80,000 full power rounds, so the barrel should last a rather large percentage of that.

    Hard chrome lined barrels have far less fouling than standard barrels, that is a fact. My FAL barrel copper fouls very slowly then cleans up in a jiffy. I had similar experience with a chrome lined Colt AR-15 barrel. I have shot both rifles to 200 rounds without cleaning at the range with only light copper fouling afterwards, somtimes in rapid fire with a very warm barrel.

    The chart seems to say better to stay away from slow powders if max barrel life is important.
     
  13. cfvickers

    cfvickers Well-Known Member

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    Just my opinion, but short shot strings, adequate cooling between shots/strings. Limit strings to 3 for best results. Most wear is due to heat limit heat, and you will limit barrel wear.
     
  14. cfvickers

    cfvickers Well-Known Member

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    Bart, your way seems like it will work, but can you put that in the form of an equation? Always hated word problems! LOL

    It also seems to go along with my theory. More powder burning= more heat built up by longer burn time. Some powders also burn hotter than others further increasing barrel heat. Remember we are talking about heat inside the bore. by the time the barrel is warm to the touch it is blazing on the inside surface. With every shot fired it is getting hotter of course. Competition shooters wear out barrels in 800-1500 rounds with certain calibers because they are often shooting 5-10 shot strings and without adequate time for the bore to cool completely. Furthermore, they are usually doing it in the summer when outside temp/sun beating down on a black barrel does nothing to aid cooling. I have about 700 rounds through my 6.5-284 and there is not yet any sign of wear and it has consistently gotten more accurate to where it has just recently hit a plateau, a good one though. I figure it has about 300-500 more rounds before it seriously starts falling off but I have not been especially kind to this barrel.