



If you get ~10 legendaries per speed run GR (not sure what the drop rates are, at GR60 speed runs I tend to get like 5-7 legendaries), that means ~230 runs to have a 99% chance of one primal. generally people put it at like 0.2% (check google), which means that to get a primal 99% certain, you need to have 2300 legendary rolls (drops). The drop rates are really low of course, before something can be primal it needs to roll as ancient, then it gets to roll as primal. If you cleared GR 70(+) solo, you are eligible for primal drops for that game type (assuming for example seasonal, softcore, you can get them on any character in seasonal softcore for this season).
