Cons are the bottles not being able to hold the pressure and blowing up. Another con is cork not being able to hold the pressure and blowing off the bottle. Finally, the cork may not seal properly resulting in flat and possibly containated beer.
Go to a bar or beer store and get some empties. Make sure they are not twist off. They should be free or really cheap.
Primary 1: Wee Heavy
Keg 1: Northern Brew #1
Keg 2: 11.11.11
Next Up: Bourbonator