Due to the differences inherent in most alloys, most people aren't going to be able to distinguish between 3.85% and 4%. Although you are correct, aren't we kind of splitting hairs here? So you have a difference of maybe a .1 on the bhn scale with your alloy. Most people probably don't even get exact measurements when adding solder to a pot. And, unless you are completely draining your casting pot before adding any additional alloy, your exact percentages are going to be off a little anyway. How close to exact same weights are your ingots when you process wheelweights?