http://optimalchargeweight.embarqspa...pes/4533485759
Sauer,check this out for ladder testing.
IMO,it could be cases,of the same brand but a different lot, neck tension[bullet grip],cartrage over all length, hot or cool barrel temp,the area that the bullet goes thru the crony[different area each shot].
Did you start with new cases or once fired from another gun? Are you using ball powder? Are you neck sizing or full length sizing?
Sauer,PERSEVERE,you will learn and beat the problem!!! While you are at it,learn a whole lot about hand loading?