I wouldn't reduce slow burning rifle powders below listed values, but its an overgeneralization that every load that only partially fills the case will cause detonations
[quoteRelax guys, these loads are straight out of the book. The IMR SR4759 is about twice as bulky as most powders and 30 gr almost completely fills it up. ][/quote]
I agree, no danger with powders of this speed. Most loading manuals are very specific about not reducing slow burners.
Read Richard Lee's treatise on reducing loads, including formulas for calculating reduced loads with different propellents in his
Modern Reloading.