AA 2520 I can load up to 47.5 grains of powder. This is a full grain beyond the hottest book max I could find. 47.8 causes gas leakage around the primer.
The old rule of thumb, even applied by Speer before they got a real pressure gun, was to load til they saw one "pressure sign" and then reduce by 6%. The point being that when you see any of the usual indications of excess pressure, you were already WELL over the SAAMI specification. A razor edge dividing line of .3 grain means that even though you don't see anything obvious, you are probably considerably over the maximum.