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Will Damage To a Rifle’s Crown Hamper Accuracy?

By Jeff Johnston

The Question: Will Damage To a Rifle's Crown Hamper Accuracy? 

If you're like me, you're nutty about preventing your rifle's crown (where the barrel's rifling is exposed at the terminal end of the muzzle) from being damaged, because it's commonly believed that crown damage can cause a bullet to exit a barrel erratically, thereby ruining accuracy. But I want to know exactly what happens when you nick your rifle's crown with a cleaning rod, grind your muzzle on gravel and dirt, take a rat-tail file to it or accidentally slip and cut the crown off entirely with a hacksaw. At worst I knew I'd ruin a few barrels and confirm what most of us already believe. But perhaps I'd find I don't have to spend the whole hunt worrying about my barrel's precious crown.

The Test
Four Thompson/Center Encore barrels were scoped and sighted-in at 50 yards. The Encore was chosen because its break-open action can better isolate the barrel. Five, three-shot groups were fired through each and group sizes were measured with the largest and smallest being discarded.

With the accuracy of each undamaged barrel recorded, one barrel was dedicated to each of four different possibilities of barrel-crown damage. One barrel was used for two tests. 

Damage ranged from common causes like cleaning your rifle from the muzzle end (mild damage), to major damage, to extreme crown desecration that should never occur to a firearm and could be dangerous. After damaging all barrel crowns, the rifles were fired again in the exact same manner as the pre-damage test, with the same ammunition, from a Caldwell Lead Sled to reduce human error. A 50-yard, indoor range was chosen to reduce variables such as wind and fluctuating temperatures. Results were compared to the original groups to determine if crown damage influences accuracy and point of impact (POI).

The Findings
In all barrels tested, barrels with a damaged crown were less accurate when compared with the rifle's undamaged accuracy data. All damaged barrels demonstrated slight to significant point-of-impact shifts. While some of the accuracy losses and impact shifts seem negligible, they will likely be magnified as range increases.

Nonetheless, if your barrel's crown is damaged, your rifle may not be ruined: In most cases, after damage, the first shot in particular and first group on average were the most erratic. But in most cases, as more groups were fired,  the groups began shrinking and migrating closer to original point of impact. If your crown is lightly damaged (the barrel is not bent nor the muzzle obstructed), fire a box of cartridges through the rifle to see if the bullet's natural honing action repairs the barrel to a usable state. If it is not satisfactory, take it to a gunsmith or have it rebarreled.

Conclusion
Yes, damage to the barrel's crown hampers accuracy. Overall, damage to the crown makes the rifle less consistent, but in all but extreme cases the rifle may still be accurate enough to continue using at reasonable ranges. But you will not know this until you shoot it at a target.

Therefore, baby your barrel! Do not clean it from the muzzle end-clean it from the chamber end. Keep your muzzle away from rocks and grit, and of course, whatever you do, refrain from cutting your barrel off with a hacksaw. The crown is best left pristine!

 

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2 Responses to Will Damage To a Rifle’s Crown Hamper Accuracy?

Adam Roll wrote:
February 10, 2012

Jeff, can you please email me? I would like to send you a pic of my new rifle. Theres a small nick at the end of the barrel. Im not sure if its the crown. The nick was there when I bought the gun NEW....

Richard Hoffarth wrote:
August 09, 2011

My father and I bought identical deer rifles at the same time. 270 BARs that shot quarter-sized groups right out of the box at 100 yards. I always cleaned my rifle from the muzzle end, being very careful not to damage the crown. After 15 years of use and cleaning, it was obvious that I was not careful enough with my cleaning rod because my father's 270 still shoots quarter-sized groups at 100 yards, while my rifle now shoots 3 to 4-inch groups. That's enough of a difference to prove to me that crown damage is a factor in accuracy...just like you said. Thank you for verifying what I had feared.