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Old March 16, 2016, 22:46   #36
MasterGunner
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FALaholic #: 15054
Join Date: Jul 2004
Location: Illinois
Posts: 520
When to Replace a Barrel

Barrel life will vary depending on how you shoot your rifle and the kind of ammunition you fire in it. For example, copper washed steel projectiles (such as Wolf and Silver, Gold, and Brown Bear) will shorten barrel life or the use of a lot of tracer ammunition will do the same thing. Otherwise, the thing you want to watch is the size of your groups at various ranges (also called dispersion). Dispersion is good for a light machine gun, but bad for a rifle. An increase in dispersion can indicate the service life of the barrel is coming to an end because it either is getting close to unacceptable chamber throat erosion or it has muzzle erosion.

Throat erosion is the wearing away of the rifling at the chamber's throat caused by a lot of rounds going down the tube. The origin of the rifling wears down and the bullet actually jumps thousanths of an inch before it engages the rifling. The bullet may be slightly off when it engages the rifling and this results in dispersion down range at the target.

Muzzle erosion is the wearing away of the rifling at the all important last two inches of the barrel (measured back from the muzzle). This can be caused by improper cleaning. An easy way to check is to use a bulleted cartridge case and insert it into the muzzle (flash eliminator or suppressor will have to be removed). The deeper the projectile goes into the barrel at the muzzle is an indication of muzzle erosion. If the bullet should go all the way down and the muzzle bottoms out on the case lip, your barrel is a candidate for replacement. Wearing away of the rifling at the muzzle allows propellant gas blow-by that acts on the bullet to destabilize it as it leaves the muzzle. Again the dispersion down range at the target will tell the tale.

To summarize, you cannot predict barrel life by the total number of rounds fired through a barrel. Barrel life is directly related to the kind and type of ammunition and how it is fired; throat erosion of the barrel; and muzzle erosion of the barrel. Shot dispersion (including unexplained "flyers") on the target is the best indication of whether a barrel is about shot out.

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Robert H. Stoner
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