It was found that the cost of the metal used to mint the coins was more than the face value of a coin denomination long back by the RBI. The first coin to have been removed was Rs. 10 coin long back. Since then the withdrawal process started. Now coming back to the withdrawal of 50 p coin is already in vogue. The next to be withdrawn is 5 rupee coin. On the whole metal coins are a burden to the exchequer financially. It's a matter of time when there will not be any metal denominations in circulation.
But do the 50P coins really exist? I haven't seen them for years now. The ones which we have in our house are lying with 5P, 10p 25 coins. Even beggars will think that you're making a mockery by giving a 50 P coin. You can try to use them in Bengal, where smaller coins are still in use.