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How To Break In a Rifle Barrel

By Nathan Foster

The subject of breaking in a rifle barrel is one of the most misunderstood aspects of the shooting sports. Often treated as a mysterious procedure, it seems that one almost needs to become a member of a ritual bound esoteric cult in order to achieve the desired results. In reality however, breaking in a barrel is quite a simple operation.

What does “breaking in” mean?

In any metal working operation, the engineer must match the final finish of the steel to the job at hand. In the dairy industry for instance, Stainless steel vessels must have a minimum 180 grit finish in order to prevent milk stone fouling or pathogens from adhering to the vessel walls during cleaning operations. In the pharmaceutical industry, 400 series stainless steel tools must have a 2000 grit finish, essentially mirror polished to prevent bacterial or viral adhesion to the steel. In the yacht industry, stainless steels must also be mirror polished to prevent salt and iron (sand) adhesion which will lead to rust if these deposits are able to settle for a length of time. In the rifle barrel making industry, the bore needs to be finished to such a level that copper fouling will not be so severe as to cause excessive fouling within the barrel. The bore must also resist corrosion.

Choice of steels (actually alloys) is one way in which the engineer can control not just the machining qualities of the steel but also the long term wear and corrosion resistance. Black or blued steel rifle barrels have low chromium but high molybdenum content which gives high strength but lower corrosion resistance than stainless steel. 416 series stainless steel has both high chromium and high molybdenum content, giving excellent strength and corrosion resistance. Both alloys can be polished to a mirror finish but only the stainless steel will hold this finish due to the oxidizing layer of chromium - providing the finish is smooth enough to prevent direct adhesion/contamination.

In the Engineering industry, the fabrication or machining of a part is performed by a fabricator or machinist while polishing operations are performed by a polisher. Nobody wants the polisher’s job as it involves heavy grinding and sometimes shaping of the steel, some welding operations, followed by fine disc grinding or buffing of the steel to the desired grade. The steel is brought to a high finish by closing up the pores of the steel until an impervious (to pathogens/corrosion/wear) layer is formed at the surface. In the mild steel sector, the finishing work is performed by blaster/ painters, another tough job.
In the barrel making industry, the finishing processes are usually performed by the machinist himself. The blank bar stock is bored to the desired caliber after which a rifled button is pulled through the bore with near un-imaginable force. Following this, the bore is lapped to the desired finish which can be done with slugs or simply by hand with abrasive pastes. The goal of this finishing operation is to reduce friction within the bore in order to minimize copper fouling. The bore does not need to be mirror finished although in certain lights, a rifle bore will often appear as though it has been mirror finished (1200-2000 grit).

A smooth, suitably polished bore cannot eliminate copper fouling. Instead, the optimum bore will foul at a very low, very consistent rate. Accurate shooting is all about minimizing variables and a bore that to a greater extent holds a very small layer of copper without any rapid build up/ change of internal conditions, has the potential to provide long term accuracy between de-fouling operations.

The finish applied by the barrel maker/machinist is dependent on two simple factors; time and money. During times of a recession or great competition between manufacturers, a price war will always result in a reduction of high labor content procedures. To this extent, lapping is one of the first operations to suffer. In other instances, where a company is under such demand that it cannot get its rifles out to the consumers fast enough to operate effectively, final finishing operations are once again, reduced to a minimum. Sometimes, a rifle barrel may have a burr on the rifling land edge, seen as long flake. If the burr is thick, hand lapping operations will fail to break it away from the land. Worse still, if the rifle has been fired several times, the burr becomes forged into a lump type anomaly, wedged into a groove. Fire lapping with a harsh abrasive is perhaps the best method of removal for this kind of burr.

Faults also occur within the barrel making process which nobody could have predicted and are sometimes un-measurable, unable to be found until the rifle is at the range. Stresses within the steel can be problem, as are changes of internal dimensions (stress reaction) due to properties of the barrel material which regardless of quality, have individual properties from blank to blank.

A custom barrel maker has more control over all of these processes. If you visit a custom barrel making website such as True-Flite or Lilja, a list of grades is presented, the highest usually termed ‘ultra match’. The difference between the lowest grade barrel and the highest grade barrel is reflective of two basic factors - labor content and grade. The ultra match bore is graded for either consistency or desirable traits of internal dimensions and then lapped to an optimum finish which requires time.

Ultimately, the end user has final control over the finish of the bore. If the bore is of a high finish, the bore will need nothing more than normal cleaning/de-fouling operations. If the bore is rough, it will need final finishing by hand which for want a better term is called ‘breaking in’ the barrel.


How to

To begin with, the rifle bedding platform needs to be in optimal condition before starting any barrel conditioning and refining operations. If the basic platform is not addressed, there will be too many variables effecting accuracy, making it impossible to observe bore finish as a single variable relative to accuracy.

Most mass produced sporting rifles benefit from action bedding, free floating the barrel and trigger tuning.  More information about these subjects can be found throughout this website. Online research will also help the reader determine whether their brand of rifle might benefit from bedding etc.

Having established a potentially accurate rifle platform, prepare the bore for its first test fire.  There are three methods of preparation that deserve consideration:
1. (Traditional) Clean the bore with a typical solvent such as Hoppe's, then dry swab the bore.
2. (Modern thinking) clean the bore, dry swab the bore, then apply a fine layer of oil to serve as a lubricant.  The Australian Palma shooting team use Rapid Tap cutting fluid.  Another product which works well is Militech-1.
3. (My own method) Clean the bore, dry swab the bore then apply powdered graphite as a fine dry lube.  I do this to minimize any chance of hydraulicing the bore, especially in overbore magnums.

Choose one of the above methods and prepare the bore for test firing.

Next, using either a reliable brand of factory ammunition (Federal is very good for testing) or carefully assembled hand loads, start by shooting a single fouling shot through the bore. The resulting shot should produce a very faint hint of copper color at the muzzle. If there appears to be a heavy coating of copper after the first shot, the bore will need to be de-fouled using a copper solvent. If none or very little copper appears after the first shot, continue with two more shots and re-observe the bore. If the bore continues to produce very little to no fouling, the rifle can be test fired / commence sighting or load development until a total of twelve shots have been fired.

Observe the bore from the same angle as viewed in the picture below.  (This bore is severly fouled)

muzzle compressed for website.jpg

To remove the copper fouling, use a strong copper removing solvent.  For many years I have used Sweets 7.62 copper remover which I apply in copious amounts to my cleaning jig, however recently, it has been brought to my attention that BoreTech also make excellent, perhaps the optimum copper removal solvents.   You will need a cleaning rod (preferably rubber coated) and an undersized bristle brush. A worn down .224 bronze brush is ideal for calibers up to .308, a worn 7mm brush is ideal for larger calibers etc. 
Use a suitably sized piece of flannelette gun cleaning rag and wrap this around around the bristle brush.  Apply the copper removal solvent to the rag until is it heavily soaked, then swab the bore. A heavily fouled bore will need several re-applications of solvent and continued swabbing.  Swab back and forth for several minutes, leave the rifle aside for 20 minutes or so, then re-apply solvent and re-swab the bore.  Throughout this operation, visually check the muzzle in order to determine when the bore has been de-fouled.  You may have to do this several times, leaving the rifle aside for 20 minute periods, until the copper is finally removed. Once all traces of copper have been removed, neutralize the bore with a swab of Hoppes No.9, then swab with dry patches until the bore is clean.
If the bore has been partially stubborn and fine traces of copper are evident after several treatments of copper solvent, neutralize the solvent with Hoppes, then move on to an abrasive as a means to remove these final copper traces and condition the bore.  Use an abrasive paste such as JB’s or Autosol, to remove minute burrs and sharp edges within the bore. These pastes start at around 1200 grit but unlike machinist lapping compounds, break down to a smaller grit size (up to 2000grit) during hand polishing. This does not mean that the bore will have a 2000 grit mirror finish, it simply means that you will be applying a fine finish to the bore.

Apply a pea sized blob of paste to a tight fitting swab, distribute the paste evenly around the swab using your fingers. Polish the bore in rhythmic strokes, quite vigorously back and forwards.  Work first on the throat, then a small amount of work through the mid section, then carefully focus on the muzzle, allowing the swab to partially, not fully exit the bore. Finally, give the bore a few full length strokes, again being careful not to allow the swab to fully exit the muzzle.  After this, the rifle will need two fresh, clean swabs, worked back and forth to remove paste residues.  Finally, prep the bore for its next test fire as described in the first three options / methods.
If the copper does not come away at all, no matter how much copper solvent is applied and no matter how much the bore is swabbed, the bore needs more aggressive abrasion. You will need to obtain 3M brand Scotchbrite. This comes in three grades, the two grades we are interested in are red (fine) and for those who can obtain it, grey (ultra fine). Scotchbrite is used throughout the metal polishing industry so please do not think this is a radical approach to abrasive polishing. Green (medium grade) Scotchbrite can be obtained from supermarkets however the red grade needs to be obtained from Engineers supply stores or surface finishing supplies stores which stock 3M brand products. Once you have obtained the  Red Scotchbrite, it needs to be cut into swabs and delaminated to a more suitable thickness. To de-laminate the pad, carefully peel the pad apart using your finger tips.


Above: Some of my cleaning kit.  The green scotchbrite is for old farm guns in need of a birthday.

Below: Delaminating Red Scotchbrite.  Norton also make a an equivalent grade (Maroon).


Below: Flannelette rag being wrapped around a .22 caliber bronze brush.


Take the Scotchbrite swab, wrap it around your worn or undersize bristle brush and check for fit in the bore. The swab should be fairly tight.. Once you have established the correct fit, pour copper solvent onto the Scotchbrite as both a copper remover and lubricant. Start the swab into the bore and give the bore a good scrubbing. The throat of your bore is a delicate area so take care not to give this area too much abrasion. The throat needs to be cleaned enough to work the Sweets into the copper and also, powder fouling which in this area, can cake hard and destroy accuracy completely. Poor case obturation, low pressures/velocity and excessive case trimming are the cause of severe powder fouling in the neck throat area of a rifle chamber. The length of the bore can be given a good work over with the pad but again, care must be taken at the muzzle. The Scotchbrite is excellent for removing minute muzzle burrs and fouling but care must be taken not to push the swab too far through and then pulled back with a severely abrasive effect. Once the Sweets or BoreTech has been worked into the bore, leave the bore for 20 minutes.  After this, repeat the first step with fresh Scotchbrite and Sweets, physically removing the copper.  Once the copper finally comes away and is completely removed, neutralize the solvent residues with Hoppes, then start over with JB’s or Autosol on a clean swab, as previously described.  For those who feel that the rifle bore is extremely stubborn, scotchbrite and abrasive paste can be used as a suitable step.  The grey scotchbrite is a great aid in this regard.

To re-cap on the techniques:


Low fouling

Copper solvent / swab / set aside for up to 20 minutes / re-apply solvent / swab / re-apply solvent / swab / observe muzzle and repeat steps as necessary.
Neutralise with Hoppe’s on swab
Dry swab / dry swab.

Mild fouling

Copper solvent / swab / set aside for up to 20 minutes / re-apply solvent / swab / re-apply solvent / swab / observe muzzle and repeat steps as necessary.
Neutralise with Hoppe’s on swab
Abrasive paste on swab / polish bore
Dry swab / dry swab.

Severe fouling

Copper solvent / swab / set aside for up to 20 minutes / re-apply solvent / swab / re-apply solvent / swab / observe muzzle.
 If after  several hours, the bore is still severely fouled,  use red Scotchbrite and solvent / Scotchbrite swab / observe / scotchbrite swab / observe.
Scotchbrite and paste can be used as an intermediate polishing step. Grey Scotchbrite very useful for this.
Abrasive paste on swab / polish bore
Dry swab / dry swab.

The goal

What we are aiming for is a bore that fouls gradually.  An optimum bore will produce light copper fouling that can be seen at the muzzle after 1-2 shots, The first or second shot may be up to an inch or so away from the normal POI.  After the bore is evenly coated with copper, it will then hopefully produce optimum accuracy for 30-40 shots before the build up of copper eventually causes fliers once again.  So what we have is a window of optimum usage, between shot number two and shot number thirty or forty, depending on the condition of the bore.

A bore that suffers excessive fouling will sometimes produce excellent accuracy for up to twelve shots as an example, then produce fliers.  What readers must understand is that the relationship between fouling and accuracy is something that can be read via visual inspection of the rifle muzzle.  No guess work is required.

Dan lilja notes that a bore with an absolute mirror finish, is like a car with bald tyres.  Always keep in mind that the goal of your bore polishing, is not to eliminate copper fouling, but to minimise excessive build up.

Other factors

A tight bore will suffer excessive fouling.  All that can be done is to continue using the steps described above, and shoot the rifle. The red Scotchbrite method should not be used all the time.  If after two or three sessions, the rifle is still severely copper fouling, it may just be that you have a tight bore that will need lots of copper solvent, lots of rag and lots of time.  The good news is that this bore is going to last you a long time and will eventually settle down after 150 rounds or so.

Chatter marks and severe burrs are common in mass produced sporters.  These can cause excessive fouling. Chatter marks can be observed at the muzzle and although they can be smoothed, it is near impossible to remove these tooling marks. 

Below: A Weatherby / Howa bore of 2010 suffering excessive chatter marks.  Unfortunately, the quality of these Japanese rifles has dropped markedly since the recession. The cost of steel has risen 100% over the last few years (chinese demand) however the price of rifles has not risen accordingly.  Low rifle prices are achieved by reducing labor content and standards of quality.

weatherby howa 7mm08 barrel 1.jpg

Just because a rifle has been purchased second hand, does not mean that it has been worn in to a smooth or high finish. Sometimes, a rifle will be in exactly the same internal condition as the day it was sold, other times, pitting may be evident as a result of poor maintenance.

Bores that produce zero fouling

A bore that does not foul is the worst possible scenario.  It means that the bore is slightly oversize and is not fully gripping the projectile. Such barrels tend to be accurate for a while, then start to show random fliers, followed by a complete loss of accuracy after around 150 rounds.

Barrel maintenance

 From time to time, it can be necessary to re-polish the barrel.   It is important to check the muzzle of your rifle on a week to week or month to month basis to see how it is performing.   As suggested, an optimum bore will suffer excessive fouling after 30-40 shots, then require complete copper removal with a suitable solvent and flannelette swabs and these cleaning sessions can be used as a means of determining current barrel condition.

If you shoot a suppressed or braked rifle, be sure to clean the carbon away from the muzzle at the end of every shooting session.  Failure to do this can ruin the muzzle and first inch of a bore by collecting moisture and ecouraging oxidization, also at times ruining stainless barrel steels.

When storing a rifle, Stainless barrels need only a coating of Hoppes or a basic fine lubricant such as WD40. Blued barrels need heavier oils if stored for long periods, engine oil is best for quarterly storage while collector pieces are best coated in heavy grease.

Always adopt some form of barrel preparation prior to shooting your rifle.  Never shoot over a heavy oil or the barrel will swell and become ruined.

In old, beaten up farm guns, green scotchbrite can be used to remove light rust from the bore as a means to keep the rifle shooting in an acceptable manner.  Many older, ex military  (Lee Enfield / Mauser / Springfield) rifles have deep cut rifling and can be revived for basic farm use after re-polishing.

How well do these polishing methods work?

These methods have been my standard “break in” or polishing procedures for several years. By using these methods along with careful observation, I have been able to achieve tangible, measurable results with great consistency.  Consistency of results was the most important factor prior to my decision to share my methods.

A while ago, a hunter brought in a factory rifle which I had previously accurised and had initially produced average groups of .7MOA. Several months later, the rifle was on my bench, the hunter beside himself with the 2.5MOA groups the rifle was producing. I asked whether the rifle had been de-fouled and was told that a cleaning kit had been purchased for the rifle, the solvent instructions followed to the letter. I took the rifle, gave it a vigorous work over with Scotchbrite and Sweets, Hoppes swab, clean swab, Scotchbrite and Autosol, rag and Autosol, Hoppes swab, clean rag swab. The procedure took some time, the fouling was stubborn but not as a result of the internal finish, rather it was due to the lack lustre cleaning kit. After this, the hunter went back to the range and shot two .7” groups.

I have a match quality custom barrel that is suffering excessive fouling?

From time to time, problems can go un-noticed during the production of a match bore - no matter how vigilant the machinist is. Sometimes, the lack of an ultra high finish may have been the result of an apprentice still undergoing the learning process. Whatever the reason, patience and understanding go a long way to resolving these issues.

If a match bore is suffering accuracy problems as a result of excessive fouling, use the Scotchbrite procedure and monitor changes after one polishing/ test fire session. If this method starts to make a difference, continue on. If however, the problem persists, contact the barrel maker and  send a macro digital photo of the excessive fouling as seen at the muzzle so that the barrel maker can see what the proposed problem is. You may even be able to come to a compromise whereby the bore is fire lapped (optimum method) followed by a re-chamber or re-throat job if the cartridge design allows for it.  Just remember, it may not be a rough bore, but rather a tight tolerance bore. 

Fire lapping with abrasive coated projectiles

Fire lapping achieves desirable results however some experimenters believe that abrasive coated bullets have a tendency to cause excessive wear within the delicate throat area of the bore. Unfortunately, evidence to the contrary has never been brought forwards (or pushed) which so far has stunted any popularity of this polishing method. That said, fire lapping does achieve what it sets out to achieve, bringing the bore to a high finish and shrinking groups right down. Some of the more advanced target shooters fire lap their bores, then re-chamber (or re-throat) to minimize any negative effect the lapping may have had on the bore.  Some of the mass produced sporters manufactured during the 2010 / 2011 recession have such poor machining marks (circular chatter marks), that fire lapping is the only option as a means of obtaining a smoothly finished bore.

Moly coated bullets

A current trend amongst target shooters is to use Moly coated bullets as a means to minimize or sometimes eliminate copper fouling altogether. An advantage of this practice is that the first shot on a clean bore will usually hold the same POI as the last shot of the day. Shooters can either use Moly coating kits or purchase pre-coated projectiles or factory ammunition.

A word about solvent cleaners

There really are a lot of traps for new players when it comes to both rifle and component shopping these days. Many of the solvents on offer are simply pathetic.  The two brands mentioned in this article are easy to obtain.


Reviving the 7mm RUM

Below, is a photo of factory 7mm RUM chamber, cut in half for inspection after firing 300 rounds.  The rifling and leade angle are showing little wear but the chamber is suffering gas erosion at the case mouth area, heavy carbon impregnation throughout the chamber and bore and a small level of gas initiated pitting (the fleck seen is pitting, not dust).

up close for website.jpg

gas cutting for website.jpg

An experiment was done, using autosol and a flannalette rag to remove the carbon, smooth the pits and revive the neck.  This did not work at all.  The carbon was fully imprgnated into the steel and the neck was too eroded.  Next, red scotchbrite was loaded with autosol and used to abrase the chamber.  This eventually removed all of the carbon, tidied the neck and smoothed the minute pits.  After this, the chamber was lightly polished with the flannelette rag and (loaded with) autosol.  The final finish was not brought up very high on this test piece.

Below, is the revived chamber.

Coming along nicely for website.jpg

So, for those of you who have a RUM barrel that is showing signs of early retirement, try the red scotchbrite on a jag followed by a soft rag, as described in the body of the above barrel break in article. As for the question as to whether this treatment will cause extra wear in an already worn chamber/throat.  Yes, this abrasion will wear away some material, especially if it is repeated every 100 or 200 rounds.  Nevertheless, if the chamber is not attended to, erosion will continue to chase rough spots, worsening accuracy at a far greater rate than any hand polishing operations.




Disclaimer/ WARNING: The views and opinions expressed in this article are solely those of the author and are not endorsed by any manufacturers. Terminal Ballistics Research and the author take no responsibility for the use or misuse of any views, opinions or information expressed in this article.


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We are a small, family run business, based out of Taranaki, New Zealand, who specialize in cartridge research and testing, and rifle accurizing.