After getting my new guitar i went about the task of putting heavy guage strings on my old, el-cheapo guitar, and tuning it CGC-FAD, just so i can experiment with downtuning. My problem is that these heavy guage strings keep going massively out of tune. Is it because my tuners are not designed for the extra strain or is it more to do with my bridge. What can i do to make this guitar stay in tune a bit more (i'm talking in 3 minutes of playing it's out of tune again).