Barrel Break-In: Can You Make a Rifle Shoot Better?

Is breaking-in a rifle barrel necessary, given today's improvements in components, manufacturing and ammunition?

Barrel Break-In: Can You Make a Rifle Shoot Better?

H-S Precision makes its own barrels, this one “broken in” by cleaning every six shots for the first 30. (Photo: Wayne Van Zwoll)

“I don’t do anything.” 

The young fellow looked me over as he might a melon he’d just opened and found disappointing.

“You mean you just shoot through it?”

“That’s what they’re for,” I replied. 

“So, you don’t season them?”

“A rifle barrel isn’t a cast-iron fry-pan.” 

His blank stare reflected a culinary past molded by McDonalds, microwave ovens and Martha Stewart on PBS.

“Now, that doesn’t mean you shouldn’t break in your barrel,” I added charitably. “Some shooters do. But it’s hard to say if those ministrations have any effect. Barrels can be as individual as puppies. If you train a bird dog one way, you can’t later say it would have fallen short trained another way.”

He saw that logic. “But barrels aren’t dogs. They’re turned out on machines programmed to make them all the same.” He held up his hands, as if to turn my next salvo. “Yes, I know barrels are made from different steels, bored to a range of diameters in different ways, cut-rifled, buttoned and hammer-forged, given various lengths and contours. But production-class barrels of identical specs from the same source should be the same.”

That logic, too, was unassailable. But on the other hand, barrels don’t always do what we expect.

Just One Example

A few years ago, I picked up a Savage rifle that I didn’t need and didn’t find very attractive. Its rubbery gray stock, little stiffer than a garden hose, cradled a hastily finished chrome-moly receiver and a plastic trigger guard. It had a blind magazine, a whippy barrel and a poorly fitted butt-pad thick enough to choke a passenger jet on a ramp. It was minimalist’s rifle, built to undersell all comers.

But it was in new condition and priced to seduce the poor. It followed me home, where I added a suitably cheap 4X scope. I cannot say why this orphan mindlessly cuts sub-3/4-inch groups with factory ammo, while much costlier rifles in my rack flirt unsuccessfully with a minute of angle. 

One reason for surprising barrel performance is in the steel. Ace barrel-makers Bill Atkinson and John Krieger have maintained that steel’s grain, inclusions and homogeneity determine not just its basic integrity but its response to stresses such as heat treating, boring and rifling. Internal variation in the structure of steel means barrels from the same source and subject to the same processes aren’t necessarily the same.

Atkinson’s experience re-rifling worn-out barrels supports his contention that accuracy can hinge on the raw steel before it’s even cut. One heavy .222 benchrest barrel won so many matches that when its accuracy faded, the owner had Bill bore it out to .308. That barrel proved as accurate in its new guise and set a world record!

Stainless and chrome-moly can both deliver one-hole groups. In either case, the best steel must be hard enough to wear well, but not so hard as to preclude machining to close tolerances. 

Of course, bores must be straight and uniform. Given modern tooling and manufacturing methods, there’s no excuse save cost-cutting to make them so. 

Rifling Affects Accuracy

Rifling type can affect accuracy too. Button rifling, commonly used on .22 Rimfire barrels but also preferred by many benchrest shooters, “irons” the grooves into the bore with a carbide button. As it does not remove material, it’s similar to hammer forging, which “kneads” a blank around a hard mandrel.

Cut rifling appeared in Nuremburg in the late 15th century. A long rod pulls a small hook in a hard-steel, bore-diameter cylinder, removing about 0.0001-inch per pass. The rod indexes to deepen each groove in turn. Rotation setting determines twist rate.

“Rifling with a single-point cutter is slow and costly but imposes little stress on the blank,” John Krieger explained. It can also produce superior barrels, thanks to the tight tolerances possible with modern tooling.

There’s no magic in groove number or depth. Many late 03A3 Springfields with two grooves shot very well. Marlin’s first Micro-Groove barrels had 16 grooves, just 0.0008-inch deep. Shallow grooves and narrow lands distort bullets less than more aggressive rifling but lose their effect more quickly with wear. Most centerfire rifles now have four to six grooves. Five-groove 5R rifling has a shallow groove-to-land angle to reduce friction and fouling and make cleaning easier. 

Finish Matters, Too

Best accuracy, say the gurus, comes from surface ripple of 10-20 micro-inches. Some barrel-makers, such as Kenny Jarrett, hand-lap bores with abrasive compound on lead plugs to polish out rifling marks. Lapping also relieves tight spots. Bill Wiseman’s cut-rifled barrels are lapped, though he told me, “dimensional uniformity trumps a smooth surface. Lapping removes only about 0.0002-inch, so it won’t fix shoddy rifling.” Krieger’s cut-rifled barrels are lapped to just under 16 micro-inches in the direction of bullet travel. Gunmaker D’Arcy Echols recalls Clay Spencer lapped barrels before and after rifling. Steve Dahlke laps Criterion barrels after stress-relieving and outside turning. 

These days, uniformity of finished bores is checked with an air gauge. A probe moving down the bore uses air pressure to “feel out” variance to 50 millionths of an inch! Jarrett’s stainless Beanfield Rifle barrels, as with Kriegers and button-rifled Pac-Nors, are air-gauged to 0.0001-inch, breech to muzzle. John Krieger cuts an inch of barrel from the muzzle to ensure against flare that can result from bore finishing.

The stresses machining imposes on steel can be “frozen out of it.” Pete Paulin of Cryo Accurizing told me “deep-freezing has been relieving such stresses since 1940. But it wasn’t practical for rifle barrels until 1992, when I learned how to overcome the resulting brittleness.” He said steel’s crystalline structure changes during fabrication. “Uneven pressure causes unpredictable expansion and contraction later. When a shot is fired, a barrel expands radially and in length. Cryogenic treatment keeps movements consistent by erasing stress that can skew them.”

The process includes a bath at -300 degrees (absolute zero, or 0 Kelvin, is -457 degrees; nitrogen liquefies at -323). “Bath time depends on the steel’s thickness. Slow cooling prevents cracking.” Paulin insists “cryo never makes a barrel worse but often improves accuracy.”

So, Now What?

With all that goes into making a barrel perfect, what can you do to improve it? Nothing.

But some shooters recommend break-in to wring all you can from it. H-S Precision manufactures the barrels as well as the stocks and actions for its super-accurate bolt rifles. It assures clients that each H-S barrel “has gone through its initial break-in during accuracy testing.” Still, H-S suggests cleaning the bore every six shots for the first 30 you fire, using this method:  

1. With Shooter’s Choice solvent on a bronze brush, remove powder fouling. Make 5 1/2 passes through the bore, removing the brush at the muzzle. Add solvent to the brush and repeat. Swab out the liquid and fouling with successive dry patches. Then repeat the entire process.

2. With Sweet’s copper solvent or Butch’s Bore Shine, remove copper fouling. Make 2 1/2 passes; then add solvent and repeat. Leave the wet bore for five minutes, then swab with dry patches. My caveat: keep ammonia-based solvents from your rifle’s mechanism, exterior steel and stock.

3. Run a clean patch through the bore and inspect for copper fouling (a blue-green stain). If that’s clearly evident, repeat step No. 2. If the patch is clean …

4. Swab with a patch soaked in light lubricant (gun oil, WD-40). Follow with a dry patch.

I’ve heard of more involved procedures but have no evidence they’re worth the bother. Frequent and thorough cleaning every few shots, and keeping the barrel from getting hot, make sense. Some barrels yield better accuracy after shooting, which you might call in-service lapping without abrasive. But bores palpably rough soon fail, as those patches snag bullet jackets. Copper buildup there scars the next bullets.

After the Break-In

What you do with a rifle barrel after initiation affects accuracy more than will break-in procedure.

Unless left to rust, barrels on blackpowder rifles endured for generations. Rifling wasn’t torched by high-pressure gas or scorched by friction from fast bullets. When smokeless powder arrived, misfires increased, because it was harder to ignite. Adding mercury fulminate solved that problem but ate brass — a chemical action exacerbated by lack of absorbent blackpowder residue.

In 1898, H-48 primers in .30-40 Krag ammunition replaced mercury fulminate with potassium chlorate. That compound spared hulls but deposited corrosive salts. The popular solution: a scrub with boiling water and ammonia or baking soda, then an oily patch. The hot water worked the magic, as it dissolved the salts.

By 1901 Germany’s RWS had a non-corrosive primer. Stateside, Remington chemist J.E. Burns developed “Kleanbore” non-corrosive priming in 1927. Peters “Rustless” and Winchester “Staynless” followed. German chemists Von Hersz and Rathburg came up with non-corrosive, non-mercuric priming. 

Dry powder and primer residues from modern cartridges won’t harm barrel steel. Both, however, are hygroscopic. Whether or not you’ve fired the rifle on a hunt, you’re smart to give the bore a couple of passes each evening with oiled, then dry patches. Don’t neglect the chamber! Sudden warmth condenses moisture on steel, so in cold weather you’re smart to keep your rifle in a cool corner of the tent or cabin. 

After a shoot, I swab a bore with a patch soaked in original Hoppe’s No. 9 (a mild solvent, with some lubricating qualities). I discard that grungy patch instead of pulling it back through. Next, I pump a Hoppes-soaked brass brush through the bore four times, back-and-forth. An MTM vise secures the rifle without marring it. Rifles await successive steps with their muzzles down, on or extended over cardboard or a canister that catches drips. I finish with dry patches, then a lightly oiled patch.

To protect the bore against rod damage, clean with a one-piece steel rod. Sections of jointed rods don’t mate perfectly. They collect dirt and scrape the bore. Wipe alloy and coated rods before and during use, to snare grit that adheres to these soft surfaces. Free-spinning rod handles let patch and brush track the rifling. A bore guide is a must. This inexpensive tube keeps the rod from flexing against the chamber. An 18mm guide fits most bolt races. Sinclair lists muzzle protectors for pumps, autoloaders and lever-actions you must clean from the front. 

On hunting trips, I bring a pull-through cable coiled in a biscuit-size pouch with slotted tip, brush, patches, a small tube of oil. The Otis Ripcord cable boasts a 10-inch section with Nomex fibers that “trap fouling better than nylon.” 

Patches should fit snugly but not so tightly that you must jam them through. Sizing matters more with brushes. Before shoving one down the bore, make sure your rod is long enough to push it clear of the muzzle! Brushes aren’t made to reverse inside! Discard brushes with tattered bristles that let the steel core contact rifling. Remember: copper solvents attack copper brushes. Use nylon brushes with these solvents.

Metal fouling can lurk in gleaming bores. Unalloyed copper is softer than the gilding metal (95-5 copper-zinc) standard for bullet jackets, so solid-copper bullets leave more stubborn deposits. Ditto lead-core bullets with “pure” copper jackets. Tackle copper fouling with ammonia-based solvents: Barnes CR-10, Montana X-Treme’s Bore Cleaner, Copper Killer 50 BMG. Rumor has it that Sweet’s 7.62 is so strong, it shouldn’t be left in the bore more than a few minutes. 

Like their jacketed brethren, cast bullets leave residue. Pure lead melts into rifling at bullet speeds around 1,200 fps. Buffalo hunters of the 1870s bumped that ceiling to 1,500 fps by adding antimony. Paper patching helped too. If cast lead bullets smear your rifling, consider making them harder or throttling back on speed. Lead removal is a mechanical process. But using any abrasive will affect the bore’s dimensions, uniformity and accuracy. H-S Precision pointedly warns against using any “abrasive/gritty cleaners.” 



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