I visited with big-name gun company engineers and owners of familiar premium barrel brands. Thankfully, they all suffered through my questions and looked past my Neanderthal-like understanding of metallurgy. My main focus was the process of breaking in new barrels, about which any two people will have three opinions. True to form, about the only thing they all agreed on was that some barrels break in easier than others. Fortunately, I pulled other gems of wisdom out of their comments that seem to jive with my own experiences.
Ever since I was taught to care for my sniper rifles' barrels in the Army, I've taken time to provide special attention to each new barrel I shoot. The degree of effort I expend depends greatly on the type of barrel I'm using and quality of internal work that went into its finishing.
Unfortunately, off-the-shelf guns often carry whatever barrel a manufacturer decides is most cost-effective. While that tube hung on the front of your favorite long-arm may look sexy on the outside, its material, rifling style, chambering and finish all affect how much break-in is needed. While opinions on this subject vary, I think most of those involved in accuracy-specific shooting disciplines will agree that the simple "load and go" approach is not the best way to initiate a new barrel.
In the simplest terms, break-in is the process of smoothing out the rough edges and tool marks left in a barrel's bore. Depending on manufacturing methods, a bore may be mirror-slick when you receive it, or it may be a few grits shy of 250 on the sandpaper scale. Firing projectiles through a rough barrel—which starts in the leade or free-bore section prior to rifling—leaves microscopic pieces of jacket deposited throughout the bore. The more rounds fired over the rough inner barrel, the more difficult it becomes to remove copper and powder fouling. If these deposits are not removed, you're left with a heavily diminished potential for decent accuracy.
Talking to the gurus solidified a notion I've had for many years: There is no single right way to break-in a new barrel. Since manufacturing methods are out of our hands when using finished barrels, we must learn to read the signs each one provides when new. As a copper or other gilding-metal-jacketed projectile moves through a rough bore, it actually provides an element of lapping action. If this material is removed before continuing to fire, the lapping process continues until the rough surfaces are polished smooth.
The important thing to remember here is that in the first few rounds it's critical to shoot, scrub and patch the bore and chamber clean after each round. While doing so, observe the level of copper fouling and degree of cleaning needed to remove it. In many cases, the process can be done in a few rounds, but occasionally I'll come across a barrel that doesn't see full break-in until 80 to 100 rounds have been through it.
I'm nowhere near patient enough to shoot one round and clean that many times. I normally use that protocol for 10 to 20 rounds before proceeding to shoot a group or two between cleanings. My progress is gauged by two critical indicators: grouping and ease of copper removal. As the bore is smoothed out groups start to tighten—often from one group to the next—and less copper is deposited. Eventually, I see my groups settle-in at about the same time the cleaning process reaches a normal level of effort. At that point, I know I can fire whatever amount of rounds is appropriate for the cartridge and barrel type between cleanings.
The methods used to clean both bore and chamber throughout the break-in process are just as important as the frequency of cleaning. I recommend using the same detailed bore-cleaning procedures you would use after a heavy range session. This should consist of using a bore brush soaked with a good solvent that will dissolve copper and carbon fouling without damaging the bore. Hoppe's No. 9 Solvent and Shooter's Choice MC #7 Bore Cleaner and Condi-tioner are both excellent choices for this task.
While ammonia-based solvents are generally OK when used according to their directions, it's very important to remove all traces of ammonia before firing or storing the rifle. According to a source much smarter than me, firing with any ammonia in the bore will result in a chemical reaction that destroys it, so diligence is required when using these potent cleaners.
Regardless of solvent type, scrub well between shots, let it soak for a few minutes (the warmer the barrel the easier the copper and fouling are to remove) then push patches in one direction through the bore repeatedly until they come out clean. If you use homemade patches, don't use colored cloth that will disguise the greenish-blue signs of copper you should be looking for. After the initial crud is removed, send a solvent-soaked patch through the barrel in one direction, let the bore soak again for a few more minutes and follow it with clean patches. If they continue to come out greenish-blue, repeat the process until they're clean.
I've come across a few rough bores that require additional work in the first few rounds. If I can't seem to get the copper out, I'll use a mildly abrasive cleaner like J-B Non-Embedding Bore Cleaning Compound until I get the fouling out.
Some companies offer projectiles impregnated with a lapping compound intended to speed the break-in process. I can't vouch for these products, but I have read some positive reviews of them over the years. I'm very wary of the paste compounds advertised to have miracle break-in assisting properties because I saw one such product destroy two premium .308 Win. barrels many years ago. The guilty company is still in business, but the specific product used is no longer available. The end result of successful, expedient break-in methods is the same as doing it the old fashioned shoot-and-clean way, so it's up to you to figure out what's best in your case.
If you have a break-in technique that works, there's no reason to change what you're doing. The important part is taking the time to do something more than simply firing a bunch of rounds and proclaiming the barrel broken-in. The results of spending more time and ammunition always pays off for me. Many of my custom AR clients don't have the budget for a premium barrel, yet through careful fitting, accurizing and breaking in, I'm able to provide them with sub-MOA rifles and carbines, regardless of barrel type.
I can't over-emphasize the importance of paying close attention to chamber cleanliness during break-in. Whenever you're going through a cleaning cycle, use a chamber brush, solvent and patches to ensure the chamber and throat receive a thorough cleaning each time.
While most folks don't have access to a bore scope, those who do will find it worthwhile to watch their bore throughout break-in. Not only are the tooling marks in a new barrel evident, copper fouling will stand out and tell you when there's more cleaning to be done.
With care, a good break-in will extend the life of your new barrel while preparing it to deliver whatever level of accuracy it's capable of. No amount of proper break-in can fix a poorly made barrel, but lack of any break-in procedures will likely limit a good barrel's life and diminish its accuracy potential right from the start.