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Shot-Out Barrels

By Ralph M. Lermayer

Shot-Out Barrels
The consistent shooting required of working a large prairie dog town can soon take its toll on a barrel, regardless of caliber.

Everyone who owns and regularly uses a great-shooting rifle lives with the concern that one day, it will lose its accuracy. Eventually it will, if you shoot it a lot. At that point, most assume the barrel is shot out. That might be the case, but before you jump to such a conclusion, you should check the obvious.

* Have the scope base screws or the rings loosened? This happens over time and is the No. 1 cause of a sudden loss in accuracy.
* Is the scope broken? Often, a separating reticle is not obvious. If the rings and bases are snug, try a proven scope before you think about a new barrel.
* Has the stock warped or shifted, and are the stock-to-receiver screws tight? Over time, a wood stock can warp, putting pressure on the barrel. Slip a dollar bill between the barrel and stock to check this. Be sure the stock screws are tight.
* Is it clean? A good, aggressive scrubbing to remove copper and lead buildup may be all that’s needed to restore accuracy.
* Has the crown been damaged? Use a magnifying glass to thoroughly inspect it. An unseen nick, rust or a chip off the crown can wreak havoc with accuracy. Any gunsmith worth his salt can easily recrown a barrel.

Assuming all the above are correct, you’re down to a shot-out barrel.

Why do barrels go bad, and how many rounds does it take to ruin one? Several factors apply.

Every shot fired takes a toll on a barrel, regardless of case or caliber. When you pull the trigger, you’re going to remove surface metal from the bore. Such wear is most notable in the throat area, forward of where the case mouth sits. This area gets the hottest flame and the heaviest pressure on firing. The area forward of the throat rarely “shoots out,” as once the bullet gets that initial hard and hot start, it has a relatively smooth ride downbore and out the muzzle.

Throats eventually erode to the point that bullets tip as they exit the case neck, and gases at the bullet’s base favor the worn-out area.

Shot-Out Barrels
Before taking the drastic step of replacing a barrel, make sure the basics are correct. Check all base and ring screws and give the barrel a thorough scrubbing to remove copper buildup.  A bore scope can reveal problems in the barrel’s throat and along its lands and grooves.

All loads do this, but small-caliber varmint rounds pushed to redline are the worst offenders. At some point, if you do a lot of shooting, the throat of your barrel will erode. What matters is, how many rounds will it take before the throat has worn enough to affect accuracy?

With the introduction of the .223 WSSM, Winchester actually tested barrel wear. They shot a standard steel barrel in .223 WSSM, a chrome-lined barrel in the same caliber and a conventional steel barrel in .22-250. Factory loads were fired in all three test guns, and throughout the test, throat erosion and accuracy at 100 yards were measured. The results are a real eye-opener, not just for evaluating the .223 WSSM, but in illustrating what actually goes on inside every bore.

The accompanying chart shows the number of shots fired and the deterioration of accuracy relative to throat wear. For those who want the minutiae, the chart shows the details, but in a nutshell, here’s what happened:

For shots 1 through about 500, erosion at the throat in both standard barrels was ongoing, but stayed under .003. Accuracy stayed at 1 inch or less. After that point, erosion increased rapidly. Accuracy between 750 and 1,000 rounds fell, coinciding with erosion measurements between .003 and .0035. For chrome-lined bores, this level of erosion didn’t occur until more than 1,000 rounds had been fired (nearly twice as much).

In that short span, groups went from sub 1 inch to between 4 and 6 inches. For the chrome-lined bores, accuracy held to minute of angle or less for over 1,500 rounds before it, too, fell  to over 6 inches. Interestingly, it took wear of only .002 to begin the loss of accuracy in the chrome-lined barrel. But it took a lot more shots to realize that erosion in the chrome barrel. Both the unchromed .223 WSSM and .22-250 behaved exactly the same, and I’m convinced that  a .220 Swift, .224 TTH or the likes of a .223 Ackley Improved would do the same.

What is happening is clear. As the throat area heats, the metal in that area is actually hardening or carbonizing. To some degree, this is an asset, as can be seen by the actual improvement in accuracy in all tests as the bore approached 750 rounds. Then, the metal hardens to a point where it becomes brittle, actually flaking off surface metal easily. From that point, erosion is rapid and accuracy falls off fast. The chrome-lined bores were able to prevent this until about 1,500 rounds, when they, too, gave out.

The magic number seems to be that once you have about .003 of throat wear on a standard barrel or .002 on chrome-lined, the barrel is shot, and that holds true for any precision-shooting rifle. That has been my experience over decades of testing with a multitude of varmint calibers from factory offerings to wildcats.

This erosion can’t be avoided, but it can be delayed. What isn’t mentioned here is how fast the shooting occurred. Heat accelerates the process. Rapid shooting, as found in rifles used to waylay endless targets in a prairie dog town, gets throats hot fast. Hot metal expands and is more vulnerable to wear. Soon, the throat area is gone. Let barrels cool between shots, and you will greatly increase their life span. Shoot 40 or 50 rounds of any high-pressure cartridge through any rifle as fast as you can load and pull the trigger, and you can kiss the barrel goodbye in short order.

The Fixes

Subscribe Today!A new barrel is the best solution, but some may opt to have the barrel removed, turned back and rechambered. This effectively cuts away the worn-out section and moves the throat farther up the barrel into new, unworn territory. It works, but your gunsmith may not be very happy about it. The problem is the carbonized area in the shot-out throat can be very tough to penetrate, often ruining an expensive reamer. Replacing the barrel will cost anywhere from $150 to The Sky’s The Limit, depending on how fine a barrel you buy. Still, you are better off replacing it. And if the rifle will see extensive shooting, fitting it with a chrome-lined barrel is a good idea.

No, the .223 WSSM isn’t any harder on barrels than a .220 Swift or a .223 Rem. All barrels wear out. How fast is up to you, and if anyone tells you different, don’t buy it unless you’ve seen the proof. Throat wear is a fact of shooting life, but it’s an easy fix. As is clear in the chart, the .223 WSSM is no more of a barrel-burner than a .22-250. With a little care, most barrels will never reach this point. For the average hunter, even 500 rounds is a lot of shooting, but the varmint hunter or those who spend a lot of time and rounds in working up a load may experience a shot-out barrel. If it happens, live with it and change the barrel. It’s no big deal and is as predictable as changing the brakes or tires on your vehicle.

Reprinted from the August 2005 issue of Buckmasters GunHunter Magazine

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