If you have every thing set properly a plastic spur well hold up fine! I run plastic in my Savage, which is about 11 pounds with well over 6 gallons of fuel through it and only replace the spur one time, do to the poor stock clutch shoes slipping so bad when new it meted the spur. I put alloy shoes in and now have well over 6 gallons on this spur and still looking good. First make sure you run good clutch shoes and the clutch is not slipping. Make sure your CB bearings are good. If you are running a Steel spur you have to run a hardened CB made to run with a steel spur. All so you have to know how to set mesh properly!
Good Luck