Does anyone know if gun raffles are legal in PA?

I live in an area of NW PA that has a lot of hunters. And my fraternity is looking into doing a gun raffle. But, I was told by a brother of mine that they are illegal to do. Is this true and what steps do we need to take in order to do this. We feel we can raise a lot of money towards our frat by doing this, but want to do it legally! Anyone of any law enforcement background who can help, it would be greatly appreciated!