Drop C tuning
I would recommend playing a lower guage for that type of tuning.
When playing in drop C tuning I use the following:
Ernie Ball Skinny Top Heavy Bottom (10-52)
Ernie Ball Power Slinky's (11-48)
Ernie Ball Nickel Medium Lights (12-54)
Be sure to adjust the nut to your string guage...
Thanks
Brian