87.5gr H1000 seems fairly light to me. I was shooting 85.5gr in a reduced charge load for my kids, and 90.0gr in a full power load with 215s in Nosler brass (same as Norma, since Norma makes Nosler's .300RUM brass).
Norma (and Nosler) brass is notoriously soft in the heads. Most leave an ejector mark even on moderate loads.
Primer cratering (if it is a consistent ridge around the firing pin hit without irregulaities) is normal in a lot of factory rifles. It comes from a loose firing pin hole. Could be another false pressure sign.
Flattened primers can be a false pressure sign at times too, caused by too much headspacing.