Barrel Life: A Screed of Old Standby & the Math of the Matter

When you talk about “barrel life”, exactly what you are talking about is of paramount importance but isn’t clarified by the simple words “barrel...
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    Barrel Life: A Screed of Old Standby & the Math of the Matter By Meccastreisand

    When you talk about “barrel life”, exactly what you are talking about is of paramount importance but isn’t clarified by the simple words “barrel life”. To some people it means the time when the gun is no longer safe to fire. To others it’s the period of time when the barrel is still able to do its job even if a bit poorly. Still others are concerned with some characteristic of how it shoots i.e. consistency of accuracy, velocity, etc… Some of us are very intolerant of a barrel being even just a little long in the tooth while others don’t really care as long as it holds together during firing. Well that complicates defining what a barrel life is now does’t it? How can one discuss anything without a basis of understanding with their audience? So, let’s just chat a bit and at the end you’ll find a very useful gift.

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    Figure 1. Black powder guns need cleaned promptly to prevent serious rusting. .45-70 Sharps 500gn LRN

    What affects barrel life is an easier thing to discuss than how long an actual barrel WILL last. Simple things like rate of fire, bullet construction, powder burn temperature, case:bore capacity ratio, rifling design are going to affect the average rifle a heck of a lot. Some of these are worse than others naturally and some can be made much worse by silliness. Complicated things like chemistry and the intersection of chemical and physical processes, things like simple cleaning, also dramatically affect barrel life.

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    Figure 2. Magnum revolver forcing cones often experience erosion. Wonder why? .357 magnum WW 110gn

    The long and short of it is, anything that applies heat or friction and many things in the way of cleaning agents/chemicals are only going to add to the wear. Anything that happens while there’s fire present is likely to be able to have fast and very severe effects compared to things that don’t involve fire. Even the most aggressive chemicals that can harm your bore, when used incorrectly take a while (numbers of minutes or hours) to do much serious damage. With fire, it’s frequently right away that the damage is done and it gets worse with each shot that happens before things have cooled. Shoot your rifle fast till it’s hot to the touch and you’re burning the barrel and shortening its life in a dramatic way. You could even burn that throat out in one bench session if you’re too zealous. Ammo doesn’t come with a shots-per-second recommendation. Ask me how I know.

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    Figure 3. 19th Century Cannon Rifling. There’s a bit of erosion.

    Chemistry. I love chemistry. Why? It’s unforgiving. Leave ammonia based copper remover in your bore too long, you’ll chemically damage it. Longer exposure with chemicals is generally always worse. Thankfully it’s pretty uncommon for shooters to improperly use really nasty chemicals on their gun. RTFM right? You can tell a nasty chemical most of the time by the smell. Folks tend to whiff a funny smell just go back and RTFM if they hadn’t before. Apart from the fact that there is a label with information on the subject to read, stink motivates curiosity.

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    Figure 4. Tight SD's are hard to get from a worn out barrel.

    To dive deeper into the discussion we’ll use a single definition of “barrel life”. It’s not valid for all discussions but it’s the way this one is being framed. For the purposes of this essay a barrel is at the end of its life when it is no longer able to provide the accuracy, reliability, safety or consistency that its use case requires. There. That’s nice and broad.

    Barrels have a life in rifles because: rifling and fire. Rifling has an origin and a terminus. Conventional rifling impresses ridges into the sides of the bullet. This is literally scraping one kind of metal against another hard enough to cause a deformation in surface profile of the softer one. Add doing this under extreme pressure and temperature and you have just defined an extreme wear area. Most guns chambered for bottle necked cases will wear the throat first by a long way. Why? Well they’re overbore. More powder than pipe so to speak. That’s also where pressure differentials are at their highest and where there’s a change in the surface profile from flat and smooth to having distinct ridges impressing themselves into the bullet.

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    Figure 5. That's five miles of gravel road right there.

    Barrel Life: A Screed of Old Standby & the Math of the Matter

    Once the start is thoroughly worn you’re unlikely to get minimally useful performance much less acceptably consistent performance. The rest of the rifling, the bore, can and usually does have a much longer “life” than the muzzle end or the rifling origin. There’s a lot of technically detailed yuk to explain that but it’s more math than needs to be written and nobody really cares to read that kind of stuff except physics geeks and materials scientists.

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    Figure 6. Counterbored rifle muzzle.

    If a muzzle is heavily eroded you might be able to lop a couple inches off and have it re-crowned and it might just last a good while longer. Could also back bore it, that is drill into it to make a new crown deeper in. Depends. If the throat is burned you can do basically the same thing. This is called “setting back” the barrel. You lop a couple inches off both ends, rechamber, re-thread and reinstall the barrel. I’ve never known anyone that’s actually done that. Probably because as I got old enough to replace barrels they were already something of a commodity item. Not nearly as big a pain to deal with as they used to be. Also, at least in the sports I compete in, the standard practice seems to be toward chasing the lands (seating bullets gradually longer and longer to keep the jump to the rifling the same) as far as you can and then tossing the pipe outright and simply getting another.

    So what you’re probably looking for is how to maximize barrel life. Well, I’m sure there are 100 opinions but there is at least one plain fact, Rule #2. I won’t judge your rules if they’re different. I bet they’ll be nearly identical though. Here’s what I do. Keep in mind, I’m not a big hunter. I’m a match/competition shooter and part time instructor. I shoot high volume when I shoot and shots are almost always done rapid fire.

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    Figure 7. Drop-in barrels are inexpensive, common and easy to install.

    As far as when to clean a rifle: By my way of doing things it is when it starts opening up the group sizes. Fouling reaches something of an equilibrium at some point where it doesn’t get much worse for each shot. This is after a period of fouling the barrel till it shoots “normal”. I find after a certain number-range of rounds my groups stabilize and my velocity SD’s thin out a bit. So I use that area to my advantage. Most of my match guns usually end up getting thoroughly cleaned after 200-400 rounds or so. If you want to clean it after a little range day, run a patch with some Hoppes #9 or CLP on it till they come out clean, then another patch dry and call it even with a final light coat of gun oil.

    My Rules for Maximum Barrel Life:
    1. Don’t clean too often. Clean when it actually needs it.
    2. Do NOT shoot your gun hot. If it’s starting to warm up, open the bolt and set it aside. This is actually Rule #1 but I like the existing Rule #1 where it's at. Shooting it hot will burn out the throat in no time.
    3. Don’t clean from the muzzle if you can possibly help it. This helps avoid damage to the crown. Avoid anything going across the muzzle in a direction bullets don’t go.
    4. Don’t push your bore brush all the way through the muzzle. When it gets there and the tip has passed partially through, pull it back. Same for patches.
    5. Never ever think that twisting/spinning a brush in your bore is a good idea. Any twisting it needs to do, the rifling will make it do.

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    Figure 8. This is a murder weapon from a rifle barrel's perspective.

    6. Don’t get aggressive with the physical part. Find a better life through chemistry. Chemical agents should be used to remove metal (copper/lead) fouling. Brushes and patches with fairly mild cleaners/solvents easily remove carbon. This is another reason to not clean deeply too often. Chemical agents for copper fouling are extremely harsh as a rule, overuse and misuse will damage barrels.
    7. Keep track of how many shots you can take before needing a cleaning. Track that over time and watch for changes. This is your barrel talking to you.
    8. Don’t shoot steel jacketed/bi-metal jacketed bullets if you like your barrel and want long barrel life. They’re pretty darned hard on barrels.
    9. Use a coated cleaning rod like a Dewey Rod and use an bore/action guide. These little things add some kit and cost but they help by keeping things lined up cleanly right off the bat, helping to prevent damage.
    10. Seriously, don’t shoot your gun hot.

    Above all, remember that like any tool rifles require maintenance but much like common hand tools, not all that much. Wipe em’ down when they’re dirty. Keep them away from moisture. Don’t let caustic agents spend much time in contact with them. Don’t get them too hot. In general, the same rules you’d apply to a Snap-On box end wrench generally apply to a rifle barrel. You don’t have to wear white gloves. These are tools that can take some rough use. You do want to have them in a condition for immediate use after you put them away so a quick wipe down, a patch set through the bore and being properly put away should suffice until it’s obvious that it’s time for a more thorough cleaning.

    All of the above is old hat for most of the folks that will read this.

    Barrel Life: A Screed of Old Standby & the Math of the Matter

    How about something I bet you don’t have but you would like? Yeah, I’m talking about new and free stuff. Yeah, that’s pretty exciting. So let’s dive in. Warning: There will be math.
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    People ask me probably 10 times a day, “How long will a barrel chambered for X last?”. I hate that question. Makes me want to bash my head on a desk because they’re asking me to predict the future and naively hoping for my answer being exactly correct. It can’t. I try to make that clear every time I give an answer. What I can do is get a useful estimate by making a horrifying number of assumptions, and so can you. What is needed is a mathematical model that describes reality within an acceptable level of imprecision. What's acceptable? In this case something to represent ideal conditions.

    Tada: Below is the equation that I use (NOTE: I did not invent it, I found it years ago) to give me an idea of my accurate barrel life. It seems really useful dealing with match rifles where 1MOA groups are simply not going to cut it. This is also not something that’s necessarily scientifically precise so please see and use it for what it is, a model. I’ve shot rifles well past the numbers produced by the equation below but they all would soon enough tell me or had already started telling me they’re giving up the ghost. That said, no firm statement of usefulness or accuracy in any particular use case is made. It's just a model.

    Variable Definitions:
    Powder Heat in KJ/kg (kilojoules per kilogram): H
    Peak Pressure in PSI: P
    Bore Capacity = (Bore Diameter^2 * 1000) / 2: B
    Powder Charge Grains: C

    The Formula for Non-Moly Loads:
    ((3800/H)^5)*3600/(C/B)^2)*55000/P

    The Formula for Moly Loads:
    ((3800/H)^5)*3600/((C/B)^2)*55000/(P - 10,000)

    So let’s do the non-Moly math for my .243AI (which is a known barrel burner). Conventional wisdom is something just north of 1000 round barrel life. Let’s see what our model says…

    First replace all the variables with numbers.
    ((3800/3990)^5)*3600/((45/29.52)^2)*55000/55000

    Next do the insides of the parenthesized sections (done in two stages here for clarity):
    (.95^5)*3600/((1.524)^2)*55000/55000 = (.7737)*3600/(2.3716)*55000/55000

    Once all parenthesized sections have been reduced, run the equation left to right:
    .7737 * 3600 / 2.3716 * 55000 / 55000 = 1199 rounds of accurate bore life.

    So yeah, the model is looking pretty accurate so far. What it cannot account for is how long of a delay between shots or how hot the barrel gets and a ton of other little things. Those things all vary radically based on the shooter, thermodynamic properties of the barrel and the effect of environmental conditions among other things. I’ve used this model for everything from .223 to .30-06 with substantial success. Try it out and see how it compares to your experience.

    Meccastreisand is a long time competitive and recreational shooter, wildcatter, computer geek, exterior ballistics geek, inventor, outdoorsman, writer, husband and father. With over 20 years of experience in local and regional airgun, handgun, rifle and shotgun competitions of all sorts he competes currently in high power and smallbore metallic silhouette in the western states and long range precision and tactical matches throughout northern and central California. In his free time he wishes that he had enough free time to do anything other than wish for more free time.

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