A look into barrel crowning and extractor cuts.
by Chick Blood
In this issue we talk about barrel crowning and extractor cuts. A rifle crown, while not regal and jewel encrusted, serves a vital purpose. It must do its part in assuring every point on the circumference of a bullet base exits the muzzle at exactly the same time. A properly cut crown will accomplish this mission. An improperly cut crown will not, allowing propellant gas to escape from one side of the base while its opposite side is still engaged with the bore. The result: Bullet tipping upon exiting the bore and potential keyholing at the point of impact.
Do you know how a keyhole hit is scored on a bullseye target? At the lowest scoring ring it contacts upon impact with the paper. Suppose you fired such a shot in a drum head tight match. One end of your bullet struck the nine ring, the other cut into the ten ring. What do you get? A nine. I don’t think anyone in the world knows for certain how many competitions have been lost by a single point. Well, perhaps there are records kept of such happenings at National, Olympic and other International shoots going back to the Creedmoor days. Never having acquired the ability to control my heartbeat prior to pulling a trigger, I’ve avoided extending a handgun or shouldering a rifle in any one of them.
Keyholing could bring about personal bodily harm if the object struck is a large game animal. I’ve heard of a reasonably placid moose being instantly transformed into a charging, enraged bull moose in mating season when a 180 grain .30-06 stung him sideways instead of entering head-on and below his left shoulder. Make no mistake, crowns on rifles are important. There are four to choose from.
Read more in our August 2014 issue. Back issues are available.