You will not how much erosion you have now without an original starting point. You can determine where your lands are now and can you reach them with loaded round.
However, erosion starts at round 1 due to the heat. Not sure what magic pixie dust disappears at round 50.
Go to www.sinclairintl.com
and look up Sinclair Seating Depth Tool, part # 09-400 at a cost of $28.95.
Easiest to use to determine where the lands are exactly and to monitor erosion.
If you have 1000 rds with that cartridge, go ahead and order another barrel now. You will need it by the time it gets to you.
Carbon ring build up in front of the chamber really destroys accuracy too. Got to use something that cuts that along with copper. Montana Extreme 50 BMG is one of the top 1k BR shooters choices for both carbon and copper.