A very crucial part of a precision rifle is its barrel. That is because it is costly, difficult to replace, vital to accuracy and precision and significant enough to determine the effective life of the rifle. Over the years, a substantial increase in the use of overbore cartridges and improvement in rifles’ design and performance which has brought significant attention to the factor of barrel life. Barrel life, according to most precision shooters is basically the number of rounds expected before the rifle shows inaccuracy of more than one minute of angle or 6 degrees at a distance of 100 yards. This level of deviation is considered “poor” and the gun is considered unsuitable for precision shooting. For top- level shooters in a competition, even half of that is enough to do away with the rifle.
Firing several hundreds of rounds, you must think that barrel life of a gun is very long, but that’s not the case. The barrel wears out in actually a few seconds. We will see the mathematics regarding that later in the article.
Barrel life is inversely related to barrel wear, i.e. the erosion of the inner surface of the barrel tube which results in the increase of diameter of the barrel. Increase in gun performances make barrel conditions worse.
Understanding factors affecting barrel life
Talking about barrel life, the first question in mind is how many rounds can be fired from a new barrel. Apparently, the answer is easy but still a bit complex. It can either be accurate barrel life or absolute barrel life. Most shooters refer to the former, as that is what matters to them. Absolute barrel life is basically the maximum number of rounds the barrel lasts. Beyond that, your gun cannot stabilize the bullet and shoots wayward. Accurate barrel life is what we defined earlier.
Barrel life is a very subjective topic and essentially depends on the purpose of the rifle and the accuracy required by the shooter. For smaller targets, like in precision shooting or hunting, barrel life is significantly smaller as the range of error in accuracy is very less. For larger and slow targets, loss of accuracy is more acceptable, thus delaying the imminent change of your rifle. Thus a barrel’s lifespan is subject to change with its purpose.
To understand the factors affecting barrel life, we need to know about barrel wear. Barrel wear occurs due to the heat and pressure the bullet generates when it travels across the tube. Barrels die out due to the erosion caused by this heat and pressure in the “throat”, the area just in front of the chamber, having the first few centimeters of the rifling. Rifling refers to grooved cuts in the barrel of the rifle. This is a normal phenomena which happens over time with continuous use of the rifle.
With increase in barrel wear, the diameter of the bore increases. This creates a gap between the rifling on the bore and the bullet in the cartridge, which makes it tougher to align and keep the bullet straight. As a result, the bullet twists in the bore before hitting the rifling and accuracy of the gun reduces, gradually. Erosion in the throat also allows accumulation of gases around the bullet, before it hits the rifling. This causes a drop in the velocity of the bullet too. That serves as a good indicator of your rifle suffering from barrel erosion. Other than erosion in the throat, cleaning the crown causes wear too.
Most barrels get “shot out” within a few hundred to a few thousand rounds. Barrel wear can happen in two forms, critical wear to the grooves of the rifling or “deepening” of existing cracks since manufacture.
What causes barrel wear?
There are several causes of barrel wear, but heat is the biggest and most common. Continuous firing from a fast, small-caliber precision rifle can reduce barrel life to a few hundred rounds. The lack of cooling time aids in the significant reduction.
The multiple factors that contribute in barrel erosion, work in tandem rather than separately. They are:
- Due to the heat and pressure, the bore surface suffers changes. The rapid heating and cooling down causes sudden expansion and contraction of the metal bore. Apart from that, the metal softens down due to continuous changes in state. High temperature melts it down while the pressure blasts the throat.
- Oxidation reaction occurs in the metal of the barrel, due to the high temperatures. This alters the molecular composition of the barrel.
- The material of the barrel matters too. Stainless steel barrels last longer than chrome-molybdenum barrels. This is down to their better heat resistance.
- Cartridge choice is the single biggest choice that determines your barrel’s longevity.
Predicting barrel life
Now, predicting the longevity is as subjective as barrel life itself. It depends on all the aforementioned factors. For a personal opinion, replace your barrel as soon as you notice a drop in accuracy.
There are specific ways to determine the barrel life. Max SAAMI pressure, case capacity and bore diameter determine that. The higher the max SAAMI pressure, the lower will be the barrel life. Pressure is also increased with increase in velocity. A slightly higher velocity, say 100 feet-per-second (fps) more won’t change much in your actual performance but can severely increase pressure and decrease lifespan of your barrel.
Case capacity is also inversely proportional to barrel life. A high case capacity means more powder to burn as fuel. Bore diameter is directly proportional to barrel life.
How to combat decreasing barrel life
These are the few methods that prevent barrel wear and improve the barrel life.
- Reduce the heat and pressure by decreasing the load. Thus, reduce the use of overbore cartridges. You might lose some velocity but will gain greatly in longevity.
- Allowing time to your barrel to cool down between shots.
- Use of coated bullets like those Molybdenum disulfide or “White graphite can double your barrel life.
- Using a slower heating powder in the case. This will reduce the heat or pressure.
- Barrel Conditioning. They are methods that extend the life by hardening and smoothening the surface, which reduces friction. Examples of that are the Melonite treatment.
- Use better cleaning methods. Firstly, clean your rifle when only needed. Ensure that you use good quality materials like chemical cleaners and carbon fiber cleaning rods. If that is a copper cleaner with high ammonia content, do not leave them for long or the steel will be affected. Avoid using abrasive cleaners. Use a snug fitting bore guide. In case you are using brushes, use soft nylon ones.
- Use barrels with a wider bore when using overbore cartridges.
Replacing your barrel
Replacing a barrel might be a solution anytime, if you have a lot of money. If not so, check for a few other factors that might be affecting your performance. Always check whether the scope is properly mounted. Continuous recoils can loosen the rings and thus the scope. If you are consistently missing your shots, check for variables like wind speed and personal errors.
Sometimes your barrel might just need some mild tuning and is not nearing its end. As we told, crown erosion is prevalent and affects your accuracy. But that can be corrected by your local gunsmith, just by “re-crowning” and costs much less. Another method is to “set back” your barrel. In this case, the gunsmith will cut off an inch of the barrel from the chamber side. This removes the most eroded part of the rifling and increases your barrel life and accuracy.
If you have checked the barrel wear yourself or got it done by a local gunsmith and are absolutely sure of making a change, only then go for it. And preferably, go for a better, more premium, custom barrel instead of a factory one, which gives a longer accurate barrel life. Ignore the last line if you are short on cash, although.
How long will a rifle barrel last?
The final and most important question. It really is contextual and depends on the shooter and frequency of use. Considering our purpose of precision-shooting, which require a very high degree of accuracy, barrel lives are smaller than other forms of shooting. That is a very generic statement although, as physics plays a big role.
Generally hotly loaded wildcat cartridge rifle barrels last anywhere from less than 1200 rounds to over 2500 rounds. Whereas mildly loaded cartridge rifles like the 308 Winchester last anywhere from 3500 to 6500 rounds before accuracy starts to drop. There have however been professional shooters with 308 Winchester rifles that have competed with barrels that have shot over 16 000 shots from the same barrel, and they still had sufficient accuracy to compete with professionally. So it depends not only on your individual cartridge and rifle factors, but also what you consider to be a worn barrel.
The lesser amount of heat and pressure you allow to generate, the slower will be the erosion. Therefore shooting slower rounds with a smaller cartridge will always lengthen the barrel life. Going for continuous rounds with a magnum cartridge can half your barrel life.
Mathematical calculation can be done about rifles, as we were talking about. Surprisingly, you average barrel’s life is around 5-10 seconds! Yes, it is that small.
Considering a bullet has a muzzle velocity of around 3000 fps, it shall take around 0.00066 seconds (approx.) to pass through a 2-feet long barrel. Considering a 5 second accurate barrel life, it can fire around 7500 rounds, which is really good. But in real-life conditions, things are slightly more complicated. This is because the muzzle velocity is much higher than average velocity. Calculating the bullet-in-barrel time, using the latter gives us a duration of about 0.001-0.002 seconds. This gives it an effective life of 2500-5000 rounds. This calculation was done by Varmint, a renowned engineer in Lawrence Livermore National Lab who shares his name with varmint rifles.
So, while a 0.308 Winchester can go good for beyond 5000 rounds in a barrel, the much faster, .220 Swift will go barely above 2000 rounds in the same barrel.
In the end, everything is not about the cartridge size itself. Different shooters use their rifles differently and also handle with different levels of care. As we already mentioned, the factors leading to barrel wear work in tandem.
Do heavy barrels last longer?
In short, no, just because the outside diameter of the barrel is larger, contains more metal, and takes longer to heat up to the point where the point of impact changes, it still does not affect the heat, barrel and throat burn happening inside the barrel. In fact, some people inadvertently shoot heavy barrels for for longer in succession before letting them cool down as they do not notice a changing point of impact from a heated barrel as quickly as when shooting with a light or sporter barrel.
What caliber has the longest barrel life?
Generally, the longest barrel lives we witness in the competitive precision shooting field comes from 308 Winchester and 222 Remington rifles. But as mentioned above, this will vary greatly from shooter to shooter and rifle to rifle.
Does fluting improve barrel life?
Fluting a barrel, increases the surface area of the outside of the barrel, so this helps the barrel cool down faster, than a normal barrel, just as a heat-sink or cooling fins on an electric motor speeds up the cooling of it, similar to a radiator. It does however not lengthen the barrel life, if the shooter still keep overheating the barrel and constantly.