I have a really nice five string Mandocaster that I had custom made for me fifteen years ago. I've always had problems with strings though. For one thing, I've never been able to find a source for mandolin sets with ball ends, so I have had to go the singles route. For this instrument I like light gauge so it's .010, .014, .024 and .036 for the E,A,D and G. I have yet to stumble on a suitable guage for the low C string. Lots of trial and error, but I have never got it to match the tone of the other four. Any help would be greatly appreciated.