Even if the stamp is on the brass rim, only the center is silver. 999 fine silver stamped either on the brass rim or on the center. With very few exceptions (Hard Rock Casino mainly) the only strikes that are silver will have. El Cortez has one machine, will have three or four plated strikes, no $300. Sam's Town has one machine in play, mostly silver plated muscle cars from the 60's & 70's but no $300. The Mirage will be introducing a new 6oz solid silver (no copper rim) $300 soon. This strike has a 6 oz silver center surrounded by copper that is silver plated. They also have a one pound $300 strike available. They are Terry Fator themed puppets, could be as many as a dozen different silver plated and two colorized silver plated in the machines now.
The Mirage has 2 silver strike machines in play, back by Revolution Theater. 999 fine strikes mixed in for players to win. In addition, there were assorted pre-2008. 999 fine silver colored strike in play and a 6 oz. Last week there were at least 10 different clad silver plated strikes in play, four colored clad strikes in play, one. Around tournament time, they add new strikes. They have six silver strike slot machines and just finished their summer tournament. The Four Queens Casino/Hotel is currently the most active property involved in the Silver Strike Program. It's been a while since your post, but just in case other's read this thread, I will chime in here with a little info.