Is there a guideline for the "life" of a barrel? I know I am nowhere near that point (only approx. 400 rounds in Model 700 Sendero SF in 7mm Rem Mag).... I am just curious. Assume a proper break-in and using 50% factory cartridges and 50% reloaded rounds at mid to top range of powder... How many rounds should I get out of a barrel before needing to consider re-barreling? Thanks in advance for comments/feedback.