Should you ‘break in’ a new rifle barrel?

Breaking in a barrel… What does ‘breaking in a barrel’ mean, and should you care about it? Well that depends on just how interested you are with the barrel’s accuracy and longevity. Make no mistake, breaking-in a barrel is a tedious, and yet necessary, process if you want to get the very most from a good barrel.

Unfortunately, the simple and straight forward procedure sure seems to be badly misunderstood, at least based on what the self-proclaimed expert knuckleheads say online. A good deal of the information posted about breaking-in a barrel seems to be unclear or misinterpreted about the why and how of the process. With that in mind, I will attempt to provide some clarity to the reasons why, and the process itself.

Understanding Break-In

Let me begin by saying that many believe the barrel to be the heart of the rifle. If that is so, and I believe it is, we should know all we can about it. As the heart of the rifle, the barrel is the foremost contributor to a rifle’s accuracy. If that is also true, the rifling must be the rifle’s soul.

I suppose, for this little treatise, I should tackle the most controversial and misunderstood concept first. “No matter who made the barrel, or how carefully it was finished, there are going to be manufacturing imperfections that only affect the accuracy of a bullet being fired through it.” So, let’s start with that.

Your new rifle or barrel was no doubt shipped to you with a short-term rust inhibitor in the bore to protect it from corrosion during storage, shipping, etc. Upon receipt of your barrel, you should first review the order and packing list to make sure the barrel matches what you ordered. If it does, clean the bore and apply a product suitable to the length of time it will be stored.

Preventing oxidation and corrosion in the barrel is your responsibility as the customer. Barrel makers are not responsible for a barrel that has been improperly stored, neglected, or abused by the distributor or customer.

It’s important to understand that even the most expensive, hand-lapped custom barrel will have a few tool marks in the barrel and throat from the chambering process and will benefit from a properly executed break-in procedure. A premium barrel, that has been finish lapped, will have the direction of the finish following in the direction of the bullet travel, so fouling will be minimal compared to a less expensive barrel with internal tooling marks.

This is true of any properly-lapped barrel regardless of how it’s rifled. If it is not finish-lapped, there will be reamer marks left in the bore. The reamer marks will be directly across the direction of the bullet travel. This occurs, even in button-rifled barrels, because the button cannot completely iron out the reamer marks.

Because the lay of the finish with a premium barrel is in the direction of the bullet travel, very little change occurs to the bore during break-in. However, the throat is another story. When your barrel is chambered, there are reamer marks left in the throat that cut across the lands and the direction of the bullet’s travel.

In a new barrel, the reamer marks are very distinct; some say they appear much like the teeth on a fine file. When the bullet is fired and forced into the throat, copper dust is removed from the jacket material and released into the gas, which at this temperature and pressure, forms a plasma. The copper dust is vaporized in this plasma and transported down the barrel. As the gas cools, the copper drops out of suspension and is deposited in the bore.

This makes it appear as if the source of the fouling is the bore when it’s actually from the throat. Copper adheres well to itself. If that copper is allowed to stay in the bore (with additional bullets and deposits fired over it), the buildup will affect performance and be more difficult to remove later. So, when we break in a barrel, our goal is to get the throat “polished” without allowing copper to build up in the bore. This is the reasoning for the “fire one shot and clean” procedure.

Every barrel varies a bit in how many rounds it takes to break in. A chrome moly barrel may take longer to break in than stainless-steel barrel, because it is more abrasion resistant — even though it is of similar hardness. Also, chrome moly has more of an affinity for copper than stainless steel, so it will usually show a little more ‘color,’ if you are using a chemical cleaner. Remember to keep the barrel clean while breaking in the throat by firing bullets through it.

That said, more affordable, lower-cost barrels are going to have more pronounced imperfections within the bore. Those imperfections are most commonly tool marks resulting from the drilling and rifling processes. Additionally, if it’s a semi-automatic, such as an AR type, there is a good chance that there could be burrs where the gas port was drilled. Those barrels will benefit even more from the break-in process.

The goal of breaking in a barrel is to have it shoot to its full potential sooner. It also means there won’t be as much copper fouling during extended use. Understand, a barrel break-in procedure does not provide a longer barrel life. However, it does provide top accuracy earlier in the barrel’s life. That results in a longer (top accuracy) life and better performance.

So, if those are things you are interested in for your barrels… The barrel break-in procedure is for you. Go ahead and knock down those manufacturing imperfections by smoothing or polishing the interior surface and burnishing the barrel steel via the bullets fired through it. Remember, the bullet is not removing metal from the barrel like an abrasive, it’s just displacing it. The bullet functions much the same as running a knife on a steel as opposed to a whetstone.

One could correctly say that all barrels eventually break-in. However, unless this is a deliberate process done at the outset, the barrel could be worn out before it’s broken in. It’s the process of firing one bullet down a clean barrel that provides the burnishing effect.

So, why not just fire one bullet through a clean barrel each time you go to the range. Then, after enough visits to the range, the process will have had its effect. The problem with that is it might not happen until after lots of trips to the range. The process I am explaining will, or should, provide the desired burnishing results in one or two intensive range session — if all goes well.

The following is a guide to “barrel break-in” based on my experience and is not intended to be detailed instructions. Some barrel, chamber, bullet, primer, powder, pressure, or velocity combinations may require more cycles than others. That means, it’s a good idea to pay attention to what the barrel is telling you with its fouling pattern and what you see on the patches. Once the barrel shows signs of having been broken in, there is no need to continue the process.

To start, you should perform the ‘shoot one shot and clean’ cycle for a minimum of five shots. Shoot- clean, shoot-clean, and repeat firing only one round at a time. If the fouling is not reduced, fire five more rounds and so on until fouling begins to drop off. At that point, shoot two shots before cleaning and observe. If fouling is reduced, fire 3 shots before cleaning. When fouling is further reduced, fire 5 shots and clean until it does not foul.

Success, and a merciful end to the tedium, is based on how much the copper fouling is reduced with each cycle. Hopefully, if it’s a “good” barrel, that will be sooner than later, and there won’t be anything showing on the patch. At that point, shoot 5 to 6 rounds and patch-clean the barrel. That’s the test, to see whether the patch comes out clean (no bluish-green residue). If so, you are done and out of your misery. The barrel is then broken in, if it indeed will break-in. Here is the procedure adjusted for different types of barrel materials.

Stainless-Steel Barrels

1. Five to 10 one-shot cycles
2. Three to 5 two-shot cycles
3. One to 5 three-shot cycles
4. One to 3 five-shot cycles

Chrome Moly Steel Barrels

1. Five to 25 one-shot cycles
2. Five to 10 two-shot cycles
3. Two to 5 three-shot cycles
4. One to 3 five-shot cycles

Additional Procedure Notes

1. Clean the powder residue from bore using a solvent such as Shooter’s Choice or Butch’s Bore Shine following the instructions on bottle.
2. Follow with a second group of patches coated in Birchwood Casey Bore Scrubber, Gunslick Pro Gun-Flush, or (for the more financially conscience) brake or carburetor cleaner from the local auto emporium or similar solvent followed with dry patches until all residue is removed from the bore.
3. With a copper remover, such as my choice Sweets 7.62 Solvent or Montana X-Treme Copper Killer to remove copper fouling. Follow the instructions on bottle.
4. With a second group of patches coated in Birchwood Casey Bore Scrubber, Gunslick Pro Gun-Flush, brake or carburetor cleaner, or similar solvent followed with dry patches until all residue is removed from the bore.
5. Run a patch that is lightly coated with a gun oil such as Lucas Gun Oil, Break Free, or a similar light oil.
6. Finish with a dry patch to remove excess oil from the bore. Firing the rifle with excess oil left in the bore can cause higher chamber pressures and is not recommended.

Dos and Don’ts

• Use a one-piece, coated cleaning rod such as Dewey manufactures.
• Use a bore guide.
• Clean from the chamber end only. Never use a stainless-steel bore brush. Do not leave strong ammonia cleaning products in your bore for extended periods of time.
• Do not allow solvents to contact the stock. They can remove the finish.

Once the barrel is broken in, remember to clean the barrel after every 20 or so rounds to keep accuracy optimal. A dirty bore is a primary cause of poor accuracy. You should understand that some barrels are going to be rough enough that a bullet jacket won’t get it done. You could shoot and clean until the cows come home, and some barrels are still going to show fouling. When that happens, I have been known to use JB Bore Paste, but that is another story.

Finally, in the spirit of full disclosure, there is also a product that was developed by David Tubb, Camp Perry Long Range champion, and national record holder. The Tubb Final Finish Bore Polishing System, which I have no personal experience with, is composed of a series of 50 bullets that are impregnated with 5 different progressively finer compounds that are designed to polish out bore imperfections. Good luck and Good Shootin’. Stay safe, train often, and practice, practice, practice!

Do you break in your gun barrels? What steps do you take? Any hints or tips about breaking in a gun barrel? Share your answers in the Comment section.