I will also add to what Expert has said by saying that it's also dependent on the pool of entries that you have. No RNG system in a program is truly random, no matter how much you seed it. If you want "true" randomness there is always this site
http://www.random.org/. As Deepbot shows you the list of entries in the order they were entered you could use this to choose a winner randomly.
Although as an example, I put a range on 1 - 10 in that website I linked and these were the results I got
8, 8, 6, 10, 8
Even with "true" randomness in 5 tries 8 came out 3 times.
Thanks,
Dante557