The Lyman Great plains bullet will throw about .504. I sent mine back to lyman and told them that Midway is selling them saying they are .508 Lyman said they were never meant to be .508 Midway offered to take it back but I have not sent it yet. My rifle does not like the Lyman great plains bullet. I can get 3" to 4" groups at best with it at 100 yards. I use a felt wad between the powder and bullet. The LEE REAL 320 is a good shooting bullet but is lighter than you want. I asked LEE and they will make you one to go 400 or even 500 gr. All it takes is money! Ron