According to the 1977 Remington Shotshell & Metallic Cartridge Component catalog the R 16 is for 1 ounce loads and the SP 16 is for 1 1/8 ounce loads.
1977 Remington 16-gauge wads.jpg
FWIW in the earlier days the 1 ounce wad was W 29932 and the 1 1/8 ounce wad W 29934.