February 06, 2023
Breaking in a new rifle barrel is a little like wizardry. If done properly, it can’t hurt and very well could make your rifle more accurate. Plus, breaking in a barrel will make it easier to clean.
Let’s start with the science behind the concept of barrel break-in. The idea is to smooth out any rough spots inside a brand-new bore. Depending on how the rifling in that bore was created, it will have various types of machining marks, overly sharp edges, and burrs. Most particularly, it’s critical to remove the inevitable burrs created by cutting the rifling leade (that area where the chamber reamer cuts a cone into the rearmost portion of the lands and grooves).
Most barrels are created by drilling an undersized hole down the length of a steel rod. Then, the hole is cut slightly larger to final size with a hone (a fine-cut drill). At this point, the hole inside the barrel is the finished size of the lands, not the grooves. The grooves have yet to be created. This honed surface has very fine machining marks inside, and even after the grooves have been cut, the top of the rifling lands (the raised part) will have slight surface marks left by the hone.
Creating the spiral grooves is accomplished one of several ways. The traditional method is called single-point cut rifling. A machine pulls a sharp cutter down the bore, removing a thin layer of steel in a spiral. The cutter is pulled through again and again, deepening slightly between passes until the groove is the desired depth. Then the cutter is rotated to a new position, and the process is repeated until the required number of grooves have been cut. It’s slow and tedious, but most of the best match-grade barrels are created using this method.
There are more modern (and slightly less controllable) methods that are effective and comprise the bulk of the production-grade barrels on the market. One is called button rifling. This process pulls an extremely hard “button” through the bore; it compresses the grooves into the barrel in one fell swoop. It takes only seconds. Savage and several other companies with excellent reputations for accuracy use this method.
Most of the European makers, Ruger, and a few other U.S. makers use a process called “cold hammer forging.” A reverse-image mandrel is placed in an over-size bore, and massive hammers pound the barrel tightly around it. Sounds extreme, right? Can it be accurate? Sako, Tikka, and others renown for accurate off-the-shelf rifles use it, if that tells you anything.
Cold hammer forging work-hardens the inside of the bore, too. Proponents claim that forged barrels last longer, and they’re probably right. Also, forged barrels are said to have less burrs and machine marks than cut or button rifling.
Whatever method is used to create the rifling, there’s still one more vital process that must be done. A chamber must be cut, and a spinning drill-type reamer is the primary way to accomplish this. Even when using the best fine-cut reamers fit with floating pilots, the cutting action is across the rifling lands and grooves. Inevitably, chambering creates burrs and leaves machine marks in front of the chamber. Removing those imperfections is the primary goal of breaking in a barrel.
That’s the science. The faith-and-wizardry part comes into play because there’s no definitive way to test the accuracy of a new barrel with and without break-in. You either don’t break it in and it shoots to a certain level, or you do and it shoots to a certain level. Even if you don’t follow a break-in procedure, the barrel does burnish over the first several dozen shots, and it will “settle.”
Break-in, however, optimizes that burnish process and gives your barrel a maximum chance at being accurate.
Without further ado, here’s how to go about breaking in your barrel.
Traditional Barrel Break-In
Before a rifle is shipped, the factory proof tests it by firing one to three “proof” loads. These are extreme-pressure cartridges designed to demonstrate that each individual action has correct strength. So even before you begin break-in, your barrel needs to be cleaned.
Clean the barrel (I’ll get to the process shortly). Fire a shot, ideally using a load with a slow, heavy-for-caliber match bullet, because they have longer shanks that apply more burnishing action to the bore, and slow bullets tend to lay down less copper fouling than fast bullets. Clean the bore again, thoroughly. Repeat the process until the barrel comes clean noticeably easier, with fewer patches and fewer passes with the cleaning rod.
At this point, fire a three-shot group, then clean. Depending on how easily the bore cleans up after three shots, you may be done, or you may need to fire one or additional three-shot groups, cleaning after each.
A barrel that cleans up easily and with minimum effort after firing three shots is most likely properly broken in.
Conceptually, here’s what the break-in process accomplishes between shots. Every time a cartridge detonates and a bullet travels down the bore, it burnishes some of the burrs and rough spots. But the remaining burrs and rough spots collect carbon fouling and tear minute amounts of copper from the bullet jacket. If not cleaned out between shots, this carbon and copper builds up quickly, actually bolstering and protecting burrs and imperfections while accelerating erosion around them.
By removing copper and carbon fouling between shots, you turn each fresh bullet into a burnishing and equalizing tool. Burrs are eliminated, sharp edges are burnished, and machining marks are smoothed.
For the actual cleaning process, always use a high-quality, one-piece rod, well coated with a nonabrasive coating. Always clean from the breech and use a bore guide to prevent wallowing out the rifling leade.
Avoid ammonia-based copper solvents. They work great for removing copper jacket fouling but also will etch and roughen your bore if left in more than a few minutes. You’re far better off taking your time with a gentler, non-ammonia solvent such as Bore Tech Eliminator or Sharp Shoot R Patch-Out (liquid) and Wipe-Out (foam) solvents.
Push several wet patches through on a snug-fitting jag. Next, wrap a patch around an under-sized nylon bore brush, wet it with solvent, and scrub the bore with it. Go back to wet patches on the jag. After three to five, they should come out quite clean. If not, repeat with the brush.
When the wet patches finally come out pretty clean, switch to dry patches. Dry the bore thoroughly. You’ll know it’s dry when the feel of the jag moving down the bore becomes slightly harder to push.
Before firing another shot, apply a thin layer of Kroil, which is most easily found and purchased online. It’s a penetrating oil that’s proven exceptionally good for seasoning the inside of rifle barrels. This helps prevent fouling from sticking.
Sound like a long process? It is. Tedious, too. Most rifle barrels take 2 to 4 hours and seven to 20 shots to break in. Candidly, I hate the process, but I’m enough of a believer that I always break it in.
Whether it made a difference or not, you’ll never know. But you’ll have the confidence of knowing you gave your rifle barrel every possible chance to shoot up to its utmost potential.
There’s a wonderful side effect, too. Whether your rifle will be a tack-driver or not is in the hands of the accuracy gods, but breaking in that barrel will make it easy to clean forever. That alone makes it worth doing.
What if you have a rifle with a seemingly unredeemable bore? What if your rifle has been shot several hundred times, and the bore is clearly still so rough inside that it takes hours to scrub clean?
There’s a process called fire lapping that can help. It’s a bit aggressive, but the good news is that it never reduces accuracy and instead increases it, and it always makes a rough bore easier to clean.
Champion competitive shooter David Tubb popularized the process and offers Tubb’s Final Finish fire-lapping kits available from Brownells or Midway. Each kit comes with bullets embedded with polishing compound, with several degrees of grit ranging from “coarse” to very “fine.”
To use, handload the bullets per included instructions using a mild charge of powder. Fire a batch of five with a given grit, clean, and go to the next finest grit. Repeat until through the finest polishing compound.
Many shooters I know don’t use the bullets with the coarser grits, opting to start somewhere in the middle. However, those coarse bullets can be necessary when starting with a rough bore that you just about can’t get it clean no matter how hard you try.
Breaking in a rifle barrel requires a lot of patience and elbow grease and possibly using up a box or so of ammo. But when all is said and done, your rifle will be easy to clean and most likely more accurate than it would have been without your hard work.