Having never shot at steel plates before, or even seen one for that matter, I was wondering what type of steel I would need for 300-400 yard plates. I would be shooting them with a 7mm RM loaded with either Hornady 139gr SST's or Nosler 140gr BT's, both at about 3200-3300 fps. I was thinking of maybe six or eight inch round plates to simulate the kill zone of a whitetail (Southern Alabama whitetail deer that is. Kinda small. Maybe should be three to six inch plates...hmmm) Regardless, if anyone could share their knowledge on this, I would be grateful.