Remington 600s and 660s should be the same, just no rib on top. Check it to be sure.
243 Winchester - 1 in 9" . . . . . . .Remington 660, 700, 788 (1969);
243 Winchester - 1 in 9 1/8" . . .Remington 700, 7400, 7600, 7;
243 Winchester - 1 in 9 1/4" . . .Savage (present)
243 Winchester - 1 in 10" Browning; Colt; FN; Harrington and Richardson
models 300, 308, 360; Husqvarna; Mannlicher
Schoenauer; Musketeer; Mossberg 800;
Remington 700, 40-XB; Savage 99, 110, 111,
112-V, 116 (old); Sako Bolt and Lever Actions;
Schultz and Larsen; Stevens 110; Winchester
70, 88,100,670,770; J.C. Higgins 51-L; Ruger 1,
77; Wichita;Weatherby Vanguard;
Thompson/Center Rifle
243 Winchester - 1 in 12" . . . . .Steyr SSG-PII
244 Remington - 1 in 10" . . . . . .Remington 700
244 Remington - 1 in 12" . . . . . .Remington 722, 760, 740, 725, 40-XB; Sako
6mm Remington - 1 in 9" . . . . . .Remington 600, 700, 742, 760, 660; Browning
B-78; Ruger
6mm Remington - 1 in 9" . . . . . .Remington 700, 4, 6, 7, 7400,7600
6mm Remington - 1 in 10" . . . . .Remington 40-XB; Schultz and Larsen;
Ruger 1, 77; Browning