While more like reading tea leaves than hard science, there are clues in determining barrel wear.
by Joe Carlos
“No one has an answer for how long a barrel will last. No one.” Glen Zediker, iiThe Competitive AR-15.
Two of the most common questions I get as an AR-15 armorer are, “How far should I jump my long range bullets?” and “How many rounds is my AR-15 barrel good for before it shoots out?” We will cover the first question in a future article. I usually answer the second with, “I have seen brand new barrels go out in as little as a few dozen rounds while others last into five figures.” The person asking assumes I am either being flip, evasive, or that I just don’t know. I plead “Not Guilty” to the first two but admit freely to the third assumption. As Mr. Zediker said, no one else has the answer either.
Most barrels wear out in the throat area where the bullet starts contacting the lands. Intuitively, most folks think that friction is the culprit, however, most barrel makers feel it is the hot, erosive gasses eating at the metal. Gradually, the point of bullet contact with the lands moves further forward, making bullets jump greater distances without any support before they enter the rifling. These same gasses also cause a gradual roughening of the back of the barrel which can be abrasive to the bullet. Often, a condition called “fire cracking” will occur. Actual rough cracks form, usually running with the “grain” of the barrel.
Read more in our June 2014 issue. Back issues are available.