saum and Gap 4s are the same. When GA Precision had Hornady make brass they named it GAP 4S meaning "Gnats Ass Precision Super Secret Squirrel Shit" I have 2, one marked 6.5 saum and the other gap 4s, I use ADG 6.5 saum brass in both. I have also used Hornady and Bertram in both. Lots of different reamer specs for the saum/4s but they all use the same brass.