3 grains over max in old milsurp brass...and a chance of wrong powder being used..... 
Give thanks to God,that it didn't let go and held together and no one was hurt...A costly lesson I am sure it will be...but one you will remember from now on...
Mac
According to my Speer manual
if indeed he is using 4350 there is no way he is 3 grains over max. at the low end if anything
