Not all Bullets are Created equal
Bullets & Pressure - A long bearing surface will make more pressure than a shorter one, when its comes in contact with the rifling. The lead alloy used for the bullet core can be hard or soft, harder making more pressure. Sierra uses 4 different alloys. A thicker jacket if used will produce more pressure. Solid base or copper bullets will be different than lead core types. So, use a starting load of powder & work up.