Perfect 70 First Strike! In addition to these being the highest possible grade, they are also signed by the 12th Chief Engraver of the U.S. Mint John Mercanti. Only First Strike coins are eligible for this designation. This special Vapor Blasted Finish Grand Canyon 5 oz Silver ATB is grade SP-70 with the special First Strike label. These coins have been specially treated after the striking process to achieve a very noticeable matte finish. This is the collector edition ATB coins and they carry the 'P' mintmark. Mintage of only 27,000 coins.