I've been shooting with both hands since I was a kid. During the summers my dad and I would play horse with .22s and make all kinds of absurd trick shots. I don't practice it a lot, but the last time I shot left handed (I'm a righty) I shot more than well enough to take a deer at the ranges I hunt.
Some people it comes naturally, others you have to practice a lot. FWIW, I also play hockey, baseball, golf and pool with both hands.