Rifle shooters have been trying to figure out a way to mitigate the effects of heat for decades, and for good reason. Heat destroys barrels.
Pushing hot, burning gas down the bore causes the steel around it to rapidly transition between solid and liquid states. It melts a little bit each time the rifle fires. The portion of the barrel that is most vulnerable and sustains the most rapid wear is the first couple inches of rifling just in front of the cartridge’s case mouth.
If you need to shoot a lot and shoot fast, don’t pick cartridges with high case volume and small calibers. Pushing lots of powder down a tiny hole is the most damaging combination for heat-induced wear. If the shooting sport or hunting scenario you participate in requires such a cartridge or creates the need for rapid fire, barrel selection becomes profoundly important.
My top pick for a barrel that I know will see some abuse would be one that’s hammer-forged. Hammer-forged barrels are not known for great accuracy (with some exceptions), but they are tough. Typical accuracy from a good hammer-forged barrel will produce around 1 minute of angle (MOA) with ammunition identified that the barrel likes.
Where hammer forging excels is in durability. The forging process involves threading a short and thick steel rod onto a mandrel and then beating the mass of steel into the final shape of a barrel. The process work-hardens all the steel in contact with the mandrel, which creates the bore. A hammer-forged barrel’s bore is the most resistant to erosion caused by heat and pressure.
Since hammer-forged barrels only come on a handful of factory rifles and many struggle to meet the needs of precision shooters, most of us shoot stainless steel barrels. This is where barrel contour and the option of barrels wearing carbon fiber become our best friends to fight the heat.
To determine how different barrel types react to rapid fire, I chose three rifles chambered in 6.5 Creedmoor. The first was a custom rifle built by Alamo Precision Rifles, which has a fluted barrel. The second was a Proof Research Switch with Proof’s carbon-fiber barrel. The third rifle was my competition gun, an Accuracy International AX308; The 6.5 Creedmoor barrel used in this test has a medium Palma contour. All the barrels were 24-inches long.
I used a cooking thermometer with a probe to measure the temperature inside the bore right at the chamber’s throat. This is the part of the rifle’s barrel that wears the fastest and suffers the most from heat. The accompanying table shows the diameter of each barrel near the throat where I measured for temperature.
The test was pretty simple: Fire 20 rounds as fast as I could through each barrel and take the bore temperature immediately after firing and again 10 minutes later. The temperature immediately after firing is the most interesting because the hotter the bore gets, the faster the throat will wear. Higher temperature means softer material, and that’s bad.
The temperature taken 10 minutes after firing is also important because it shows how fast a barrel can recover from the heat. Faster recovery times mean the shooter can start firing again sooner without damaging the barrel. This is advantageous for match competitors who move from one shooting stage to the next.
The barrel contour of the two stainless steel barrels bears consideration. The fluted barrel was .1-inch smaller at the throat than the unfluted barrel and yet there was quite a difference in temperature between the two.
The day I did the test, the ambient temperature was 86 degrees Fahrenheit. The fluted barrel had a bore temperature of 160 degrees immediately after firing and 125 degrees 10 minutes later. The unfluted barrel had a temperature of 151 degrees after firing and 107 degrees 10 minutes later. The Proof barrel was 189 degrees right after firing and 129 degrees 10 minutes later.
Most shocking was the effect on bore temperature the additional .1 inch and absence of flutes had on a stainless steel barrel. I can’t tell you how often I’ve heard the refrain “flutes help a barrel cool faster because of the fluted barrel’s increased surface area.” This simple test disagrees. Mass is the answer for dealing with heat.
Heat conduction in a barrel is a more efficient method of evacuating heat from the bore than convection at the barrel’s surface, as this test demonstrates. The more steel there is in a barrel, the more it works like a heat sink. Remove steel and the heat has no place to go except to the surface. Flutes do increase the surface area of a barrel, but don’t help much in reducing bore temperatures.
The oddball of this bunch is the Proof Research barrel. The use of carbon fiber is hands-down the best way to reduce barrel weight. Carbon fiber is also a rigid material and rigidity makes for an accurate barrel. Every Proof barrel I’ve tested has been very accurate.
Proof Research spends a lot of time and effort on getting their carbon-fiber barrels to efficiently evacuate heat. The epoxy that holds the carbon fibers together is continually improving and one of the main objectives is to transfer heat from the bore to the barrel’s surface. Proof barrels do this job very well. However, a carbon-fiber-wrapped barrel consists of a thin stainless-steel liner (think of it as a very skinny barrel) surrounded by the fiber. As this test shows, the bore got hot quickly.
This test also validates the science behind Proof’s thermal conductivity. The barrel’s temperature was 29 degrees higher than the fluted barrel, but cooled to almost the same temperature 10 minutes later. The Proof barrel may have become the hottest of the three test barrels, but it also cooled the fastest. If your shooting sport has stages where weight is a consideration, carbon-fiber barrels are the answer.
Fueling the Fire
Probably the single biggest indicator of how quickly a barrel gets hot is cartridge case capacity. Powder in the case is fuel for the fire. The more fuel, the more heat that comes from it. If you choose a high-volume case, you must embrace the baggage that comes along with the performance.
The toughest combination of all, and the problem for which there is no solution, is a lightweight rifle paired with a high-volume case. A barrel on this rifle will have a short service life, but my top barrel pick would be the carbon-fiber barrel. That barrel is going to get hot and there isn’t a lot anybody can do about it, but at least the carbon-fiber barrel is light and sheds the heat quickly.
As much as lighter rifles always seem to be desirable, leaving steel on the barrel is the single best way to keep bore temperatures down. This extends barrel life and allows the shooter to shoot a more abusive firing schedule without rapidly destroying the barrel.
The next time folks get in a discussion about cartridges that “burn barrels,” bring up that barrel contour contributes significantly to how long a barrel lasts. No one ever discusses barrel contour with barrel life and that’s unfortunate. Every time someone gives an estimated barrel life for their pet cartridge, it would be beneficial to all to include the barrel contour that afforded its longevity.