Barrel Break In

Off To A Good Start 
by Stuart A. Leach a.k.a. “the Colorado Gray Fox”

Modern gun makers have devised a number of ways to create the long tubes of steel with internal spiraling grooves we call rifle barrels. All start with a blank bar of metal; from there divergence in methods and sequence of operations grows quickly. Some barrel makers do all outside machining before boring, reaming and rifling, others do the opposite. Those spiraling grooves are created through cutting, scraping, broaching (a series of cutting edges on one tool) or hydraulically forcing a reverse image tool through the bore. Hammer forging combines outside shaping with internal dimensioning and rifling. Some makers straighten barrels; others are vehemently against this. Lapping with fine abrasives may or may not be done at various stages. Great barrels are produced by all the varied processes.

The finest attention to detail still leaves some minute roughness inside a new barrel. Chambering leaves some roughness in the leade and throat areas. These microscopic grooves, rings, pits and fins tear at the outside of a bullet as it passes by, causing some of the jacket material to remain behind. Successive shots add to this; residues from primer and powder combustion add to the chemically active mix. As a string of shots progresses the deposits build up, creating constrictions and uneven passage of the bullet through the bore. Barrel vibrations become less uniform, and accuracy suffers.

Think of a firearm as a very simple internal combustion engine. The barrel is the cylinder, the bullet is the piston. In this “free piston” engine we use each piston only once, but we expect several thousand functions from the cylinder. Two dissimilar metal surfaces must move past each other at high speed, under great pressure and with little or no lubrication. Careful break-in of the cylinder will enhance accuracy, allow longer accurate strings between cleanings, ease the cleaning process and extend the life of the barrel. Any barrel will benefit from proper break-in, be it the chrome-moly steel tube on a mass produced hunting rifle or the stainless steel product of the finest custom maker.

Break-in is done at the range, and takes a long morning or afternoon. A series of shots is fired, in combination with very thorough cleanings. The objective is to have successive bullets pass by bare steel, acting to wear down microscopic irregularities and impart a final polish to the barrel. The soft metal bullet jacket has an action much like the effect of a leather strop on a straight razor. Minor rugosities which rise above the base surface of the steel are wiped away.

In addition to the rifle and appropriate plain bullet ammunition the following will be needed:

* Padded cradle or vise to hold the rifle
* Cleaning rod guide
* High quality plastic coated cleaning rod 
* Bronze bristle brush
* Plastic or boar bristle brush, or bore mop
* Spear or wrap around patch holder
* Ample supply of patches
* Powder solvent such as Hoppe’s, Shooters Choice, etc.
* Copper solvent such as Sweet’s 7.62, or abrasive cleaner such as JB Bore Paste
* Wiping rags

Before firing the first shot wipe out the barrel with powder solvent and patch dry. Some pretty strange things can get in a barrel during final assembly and shipping, let alone while on a display rack. Firing that first shot without cleaning risks damage to the bore.

Fire one, and only one, shot and clean well with powder solvent, bronze brush and patches. Always use an eye dropper or squeeze bottle to apply the solvent to the brush; dipping the brush in the bottle just contaminates your whole solvent supply. Wipe the rod between passes. Now clean again with copper solvent. Apply the copper solvent with the plastic or boar bristle brush, or with the mop- this stuff eats bronze brush bristles! Apply liberally, and allow to work for three to five minutes. Position the rifle with the muzzle low to keep solvent from draining into the action and bedding. I like to dry fire, shoot another gun, shoot the breeze, etc. while waiting.

The first patch after applying copper solvent will show a lovely azure blue color. This is made up mostly of copper compounds, the products of a chemical reaction between bullet jacket metals and the ammonia in the solvent. Patch dry, apply more copper solvent, wait, and patch again. Repeat this regime until no blue color shows on that first patch. The barrel must be cleaned down to bare steel.

Some custom barrel makers recommend that each shot be fired across clean, dry steel uncontaminated by powder fouling or jacket material. Alternatively, some well respected benchrest gunsmiths recommend a “wet” break-in, where the barrel is cleaned as described and a light coating of Rem Oil ™, Kroil ™ or a similar light bodied oil is applied before the next shot is fired. Both schools emphasize one shot at a time, and thorough cleaning. Some ‘smiths and barrel makers are also endorsing use of the mild abrasive cleaners such as JB Bore Paste, Rem Clean or IOSSO.

Fire another single round, and clean again. Keep this up for at least ten rounds, fifteen would be better. After a few rounds you will find fewer doses of copper solvent are needed to get a clean patch. The break-in process is progressing. A Rocky Mountain Rifle Works (Mark Chanlynn) 30 caliber match barrel needed fewer doses after just five rounds; a Norinco SKS never did need fewer doses.

Finally, fire a series of three shot groups, cleaning as before. After three to five groups and cleanings the break-in process is complete. Shoot well, being confident that you have done your part to enhance barrel performance.