Use a whole glass bead new at a 100-170 grit (NO. 10). That is what will match a glass beaded action. I have never had any of mine rust either. You can grab 50 lbs from ZORO part# G0700563 for 61.26. If you dont need that much grab 10 lbs from amazon. Just make sure you grab the whole glass and not crushed. Aluminum in the 120 grit is great for SCRATCHING for duracoat/cerakote. Otherwise the Glass peens the surface. If you go to a course grit like 60-80 it will look dark gray, but from most manufactures I have talked with use the 100-170 to peen their actions with.