Competitive shooters (who place a high value on accuracy) will replace their barrels a lot more often than that.
Some of the top 3 gun shooters in the US talk about 2,000 to 3,000 rounds as the "sweet spot" for their customer AR barrels, afterwhich accuracy starts to fall off and they start looking at replacing the barrels. Keep in mind they mostly use either Stainless (softest but most accurate) or Chrome-Moly (next best). The chrome-lined barrels will last longer BUT they are not as accurate to begin with.
Guys who talk about 50,000 and 100,000 rounds out of their guns often don't mention that the barrel has been replaced along the way... nor do they talk about the accuracy loss that's occurred.
I have a PPC Revolver that probably has 100,000 rounds through it and it's still incredibly accurate, however, it shoots nothing but low velocity, competition load ammo, soft lead only (no plated or jacketed) and so there's almost no stress on the barrel... not enough to 'shoot it out'.
On the other hand my S&W Performance Center PPC9 will start to experience loss of accuracy around 5,000 rounds and would likely need a barrel replacement before 10,000 rounds. That's not to say that the gun won't still shoot and even shoot well... but when you're looking for 1" to 1.5" groups at 50 yards you can't expect this barrel to perform that way with 50,000 or 100,000 rounds through it.
It comes down to what type of accuracy you expect from the gun, what type of ammo is being used, etc..
Besides... if you can afford to shoot 50,000 rounds through your gun (which is something like $7,500 to $15,000 worth of ammo if not more) then you can afford to change your barrel to maintain a high degree of accuracy.
Mark
