I picked up some 300 H and H mag brass and have sized the neck only until the case is tight (touching the 30 cal part of the shoulder). this is to be fire formed in a 257stw rifle. I need to know what would be a good load for this. I have a very wide selection of powders on hand. The 300 h mg brass is on 25 thousandsth shorter .I am considering using standard load data for the 257 weatherby.as this case is about 1/3 inch shorter. Can anyone help,please ?