Shifting coins between alt and btc on an exchange can give you nice results 
I think its to risky to do that, its mostly not profitable.
I tried it multiple times, but only got a little profit.
Other are making profit out of that method. And yes risk are there that's why you need to properly execute your every trading moves.
Why not try the exchange trade of BTC to USD if you found yourself having a hard time doing altcoin exchange.