Most expanders are designed to .001 to .002" smaller than the bullet. For example the 577/450 Martini Henry dies ship with a .468 expander for a .470 bullet.
We can make a custom over sized expander if you send in a sample bullet. Cost is $30.00 plus any applicable taxes + Shipping/Handling. Please call us to place an order, our phone number is (262) 673-3075.
