You can read all that you want but it comes down to knowing your gun and hours of practise on a regular basis.If you want to be able to accurately place bullets at 400 yards you will have to shoot regularly at all distances out to 400 yards.This will require a lot of time and ammunition but you simply can't develop and maintain long distance shooting skills any other way.Shooting a few boxes of ammunition per year is not going to do it no matter how much you read and how many tips people give you.If you are really serious about this ,expect to fire at least a couple of hundred rounds out of your deer rifle per year practising.