I magazine per rifle and that's all. We did occasionally have to reject magazines but generally only because they were totally worn out or wouldn't fit tightly at the back-strap. We used to adjust magazine lips to feed every day, day in and out. You just have to look at what's going on slowly from above and adjust accordingly. It's just experience and every magazine fits and operates differently in every rifle. That's why they're numbered - because they are individually fitted.
As a matter of interest we'd occasionally have a big purge and get together 50 or so magazines with worn back straps, cut the strap back, silver solder a new section in and remake to new leaving the strap slightly long. Then use these magazines while rebuilding other rifles needing magazines. Bar out old and re-number to suit new rifle. We didn't waste much