The chrome lined barrel in your SKS will last a very long time if you take minimal care of it, especially after shooting the older corrossice ammuniton. SKS rifles are very durable and rugged military issue rifles that were made primarly for peasant armies that recieved a minimum of training. Don't worry about your SKS it will last longer than you will....
1500 to 2000 rounds. Or so I am told by actual barrel makers. Thats the average life span of the chrome lining. After that - it's a matter of how you take care of it.