It depends.

• The grade of steel the barrel is made out of will affect longevity.
• Chrome plating or surface nitriding versus nothing at all can impact longevity.
• What the jacket of the bullet is made out of can affect longevity.
• How fast you fire (and the resulting heat of the barrel) can affect longevity.

This is a link to a "torture test" in which rifles were intentionally abused to see what impact some of these factors would have on the life of the barrel.

http://www.luckygunner.com/labs/bras...el-cased-ammo/

Note that although the article is captioned as a comparison of brass versus steel "case" ammunition, the effect of gilding metal jacketed bullets versus bi-metal bullets are also addressed.

In this abusive situation the barrels firing the bi-metal bullets were shot out by around 6,000 rounds while the barrel shooting the gilding metal bullets was still servicable after 10,000 rounds. I would think that gently used barrels would last at least that long.