Be careful when tuning strings, especially E, up (higher). The finer the string, the more sensitive it is to tightening. If you make the E string just a little too tight with the peg, it certainly will snap. Use fine tuners, especially on the E string. Loosen the string before tightening it to decrease the risk of snapping it. Since your trouble was especially bad after using peg dope, you may have used too much. It should be used sparingly. If you used too much, the peg would be hard to turn, you use force, and bingo-- the string snaps. Don't pull or yank on a string to increase its elasticity, as guitarists often do. Fiddle strings are very different from guitar strings. BTW, what kind of fiddle strings are you using? There are many kinds, all with very different physical properties. Fiddle is a complex instrument even though it only has four strings. They call it the devil's instrument for many good reasons. Tuning is a lot more complex than it looks. Be gentle with the fiddle. You really should get a teacher. Fiddle is a very technical instrument. You have to do a lot of things by learning how they feel. Verbal descriptions will not suffice. You need someone to watch what you're doing at frequent intervals (weekly). I can't overemphasize the importance of getting a good teacher.