MH - It seems like you want to be generous and have a raffle. But $50 is pretty steep for a lot of guys. Maybe you could do the same thing for - maybe $10 and document everyone's name who entered. Then if you don't get 20 sign ups you can return their money. But like you did before, state that 20 need to be sold and if a minimum of 20 are sold by (date) drawing will be on (date).
Or you can do what MD says and just put it up for sale for $200.
First though, I think I would ask the moderators if you can do this. There is a classified section here on the forum and they might want you to post it there.
Or even better - yo can say you are giving away the rifle and bullets. S&H $200.