There are a lot of variables to this, so it is difficult to come up with numbers. But here are some variables:
Bullet weight - Heavier bullets wear barrel faster than light bullets.
Barrel material/fabrication method - It's generally agreed that cut rifled barrels last longer than button rifled, and hammer forged lasts longer than cut. Walther claims their stainless material lasts longer than 416, and chrome lined lasts longer than plain. HK & Noveske claim their polygonal rifling lasts longer than conventional rifling.
Velocity - High velocity wears faster than the same bullet moving slow.
Bullet style - It's been noticed that many barrels that won't shoot boat tails will still shoot flat base.
Cleaning method - Using poor cleaning methods can damage a barrel, especially the crown.
Fire lapping - It is claimed that fire lapping extends the life of a barrel.
Then last, but certainly not least, Your accuracy standards - A barrel that is too worn for benchrest use might be just fine for whacking P-dogs or for 3-gun competition.
